Kiniksa Pharmaceuticals (KNSA) 10-K 5 Mar 20 2019 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Feb. 29, 2020	Jun. 30, 2019
Document information
Document Type	10-K
Document Period End Date	Dec. 31, 2019
Entity Registrant Name	Kiniksa Pharmaceuticals, Ltd.
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Public Float			$ 304.6
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Central Index Key	0001730430
Amendment Flag	false
Common Shares
Document information
Entity Common Stock, Shares Outstanding		55,547,374
Class A common shares
Document information
Entity Common Stock, Shares Outstanding		20,388,482
Class B common shares
Document information
Entity Common Stock, Shares Outstanding		4,105,320
Class A1 common shares
Document information
Entity Common Stock, Shares Outstanding		14,995,954
Class B1 common shares
Document information
Entity Common Stock, Shares Outstanding		16,057,618

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 46,928	$ 71,976
Short-term investments	186,452	235,328
Prepaid expenses and other current assets	8,247	6,446
Total current assets	241,627	313,750
Property and equipment, net	6,398	6,356
Operating lease right-of-use assets	1,927
Restricted cash	210	210
Deferred offering costs	0	433
Deferred tax assets	4,372	1,216
Total assets	254,534	321,965
Current liabilities:
Accounts payable	5,693	10,918
Accrued expenses	20,415	16,418
Accrued milestones		15,000
Operating lease liabilities	1,697
Other current liabilities	25	218
Total current liabilities	27,830	42,554
Noncurrent liabilities:
Noncurrent operating lease liabilities	955
Other long-term liabilities	326	144
Total liabilities	29,111	42,698
Commitments and contingencies (Note 13)
Shareholders’ equity:
Additional paid-in capital	581,467	473,483
Accumulated other comprehensive income (loss)	33	(4)
Accumulated deficit	(356,092)	(194,225)
Total shareholders’ equity	225,423	279,267
Total liabilities and shareholders’ equity	254,534	321,965
Class A common shares
Shareholders’ equity:
Common stock value	6	4
Class B common shares
Shareholders’ equity:
Common stock value	1	1
Class A1 common shares
Shareholders’ equity:
Common stock value	4	4
Class B1 common shares
Shareholders’ equity:
Common stock value	$ 4	$ 4

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Class A common shares
Common stock, par value (in dollars per share)	$ 0.000273235	$ 0.000273235
Common stock, shares issued (in shares)	19,245,201	19,245,201
Common stock, shares outstanding (in shares)	15,797,220	15,797,220
Class B common shares
Common stock, par value (in dollars per share)	$ 0.000273235	$ 0.000273235
Common stock, shares issued (in shares)	4,638,855	4,638,855
Common stock, shares outstanding (in shares)	4,638,855	4,638,855
Class A1 common shares
Common stock, par value (in dollars per share)	$ 0.000273235	$ 0.000273235
Common stock, shares issued (in shares)	14,995,954	14,995,954
Common stock, shares outstanding (in shares)	12,995,954	12,995,954
Class B1 common shares
Common stock, par value (in dollars per share)	$ 0.000273235	$ 0.000273235
Common stock, shares issued (in shares)	16,057,618	16,057,618
Common stock, shares outstanding (in shares)	16,057,618	16,057,618

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Operating expenses:
Research and development expense	$ 135,001	$ 86,597
General and administrative	34,962	21,563
Total operating expenses	169,963	108,160
Loss from operations	(169,963)	(108,160)
Interest income	6,049	4,719
Loss before benefit for income taxes	(163,914)	(103,441)
Benefit for income taxes	2,047	214
Net loss	$ (161,867)	$ (103,227)
Net loss per share attributable to common shareholders - basic and diluted	$ (2.99)	$ (3.49)
Weighted average common shares outstanding - basic and diluted	54,049,477	29,547,427
Comprehensive loss:
Net loss	$ (161,867)	$ (103,227)
Other comprehensive income (loss):
Unrealized gain (loss) on short-term investments and currency translation adjustments, net of tax	37	(4)
Total other comprehensive income (loss)	37	(4)
Total comprehensive loss	$ (161,830)	$ (103,231)

CONSOLIDATED STATEMENTS OF CONV

CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED SHARES AND SHAREHOLDERS (DEFICIT) EQUITY - USD ($) $ in Thousands	Convertible Preferred Shares (Series A, B and C)	Common SharesInitial Public Offering	Common SharesFollow-On Offering	Common SharesPrivate Placement	Common Shares	Additional Paid-In CapitalInitial Public Offering	Additional Paid-In CapitalFollow-On Offering	Additional Paid-In CapitalPrivate Placement	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Initial Public Offering	Follow-On Offering	Private Placement	Total
Balance at the beginning of the period at Dec. 31, 2017	$ 119,770
Balance at the beginning of the period (in shares) at Dec. 31, 2017	22,885,492
Changes in temporary equity
Issuance of Series C convertible preferred shares, net of issuance costs	$ 190,822
Issuance of Series C convertible preferred shares, net of issuance costs (in shares)	12,784,601
Conversion of convertible preferred shares to common shares	$ (310,592)
Conversion of convertible preferred shares to common shares (in shares)	(35,670,093)
Balance at the beginning of the period at Dec. 31, 2017					$ 1				$ 1,289		$ (90,998)				$ (89,708)
Balance at the beginning of the period (in shares) at Dec. 31, 2017					4,288,329
Changes in equity
Conversion of convertible preferred shares into common shares					$ 8				310,584						310,592
Conversion of convertible preferred shares into common shares (in shares)					35,670,093
Issuance of common shares upon completion of offering, net of underwriting discounts and commissions and offering costs		$ 4				$ 155,532						$ 155,536
Issuance of common shares upon completion of offering, net of underwriting discounts and commissions and offering costs (in shares)		9,484,202
Exercise of options									377						377
Exercise of options (in shares)					47,023
Share-based compensation expense									5,701						5,701
Unrealized gain (loss) on short-term investments and currency translation adjustments, net of tax										$ (4)					(4)
Net loss											(103,227)				(103,227)
Balance at the end of the period at Dec. 31, 2018					$ 13				473,483	(4)	(194,225)				279,267
Balance at the end of the period (in shares) at Dec. 31, 2018					49,489,647
Changes in equity
Issuance of common shares upon completion of offering, net of underwriting discounts and commissions and offering costs			$ 2				$ 48,474	$ 34,511					$ 48,476	$ 34,511
Issuance of common shares upon completion of offering, net of underwriting discounts and commissions and offering costs (in shares)			2,816,110	2,000,000
Common shares issued or to be issued in connection with the acquisition of all issued and outstanding equity securities of Primatope Therapeutics, Inc.									7,000						7,000
Common shares issued or to be issued in connection with the acquisition of all issued and outstanding equity securities of Primatope Therapeutics, Inc. (in shares)					337,008
Common shares issued or to be issued in connection with a milestone payment due to Primatope Therapeutics, Inc.									1,800						1,800
Common shares issued or to be issued in connection with a milestone payment due to Primatope Therapeutics, Inc. (in shares)					94,284
Exercise of options									1,119						1,119
Exercise of options (in shares)					200,579
Share-based compensation expense									15,080						15,080
Unrealized gain (loss) on short-term investments and currency translation adjustments, net of tax										37					37
Net loss											(161,867)				(161,867)
Balance at the end of the period at Dec. 31, 2019					$ 15				$ 581,467	$ 33	$ (356,092)				$ 225,423
Balance at the end of the period (in shares) at Dec. 31, 2019					54,937,628

CONSOLIDATED STATEMENTS OF CO_2

CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED SHARES AND SHAREHOLDERS (DEFICIT) EQUITY (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Series C convertible preferred shares
Issuance costs	$ 9,178

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (161,867)	$ (103,227)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	2,068	286
Share-based compensation expense	15,080	5,701
Class A common shares issued or to be issued as consideration for Primatope, including milestone payments	8,800
Loss on disposal of property and equipment	21	66
Other		235
Non-cash lease expense	1,211
Accretion of discounts on short-term investments	(3,501)	(1,423)
Deferred income taxes	(3,156)	(978)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,020)	(4,791)
Accounts payable	(4,705)	8,823
Accrued expenses and other liabilities	4,638	9,296
Accrued milestones	(15,000)	5,000
Operating lease liabilities	(1,264)
Other long-term liabilities	326
Net cash used in operating activities	(158,369)	(81,012)
Cash flows from investing activities:
Purchases of property and equipment	(3,203)	(5,290)
Purchases of short-term investments	(488,773)	(402,008)
Proceeds from the maturities of short-term investments	541,190	168,100
Net cash provided by (used in) investing activities	49,214	(239,198)
Cash flows from financing activities:
Payments of offering costs	(118)	(3,657)
Proceeds from exercise of options and employee share purchase plan	1,119	377
Net cash provided by financing activities	84,107	346,736
Net increase in cash and cash equivalents and restricted cash	(25,048)	26,526
Cash, cash equivalents and restricted cash at beginning of period	72,186	45,660
Cash, cash equivalents and restricted cash at end of period	47,138	72,186
Supplemental information:
Cash paid for income taxes	1,724	383
Supplemental disclosure of non-cash investing and financing activities:
Deferred offering costs included in accrued expenses and accounts payable		404
Property and equipment included in accrued expenses and accounts payable	222	1,292
Series C convertible preferred shares
Cash flows from financing activities:
Proceeds from issuance of convertible preferred shares, net of issuance costs		190,822
Initial Public Offering | Class A common shares
Cash flows from financing activities:
Proceeds from issuance of common shares, net of underwriting commissions and discounts		$ 159,194
Follow-On Offering | Class A common shares
Cash flows from financing activities:
Proceeds from issuance of common shares, net of underwriting commissions and discounts	48,595
Private Placement | Class A1 common shares
Cash flows from financing activities:
Proceeds from issuance of common shares from private placement, net of underwriting commissions and discounts	$ 34,511

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	12 Months Ended
	Dec. 31, 2019
Nature of the Business and Basis of Presentation
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation Kiniksa Pharmaceuticals, Ltd. (the “Company”) is a biopharmaceutical company focused on discovering, acquiring, developing and commercializing therapeutic medicines for patients suffering from debilitating diseases with significant unmet medical need. The Company was incorporated in July 2015 as a Bermuda exempted company. The Company has a pipeline of product candidates across various stages of development. The Company is subject to risks and uncertainties common to early‑stage companies in the biotechnology industry. There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s technology will be obtained, that any products developed will obtain necessary government regulatory approval or that any products, if approved, will be commercially viable. The Company does not currently generate revenue from sales of any products, and it may never be able to develop or commercialize a marketable product. The Company has not yet successfully completed any Phase 3 or other pivotal clinical trials, obtained any regulatory approvals, manufactured a commercial‑scale drug, or conducted sales and marketing activities. The Company operates in an environment of rapid technological innovation and substantial competition from pharmaceutical and biotechnological companies. In addition, the Company is dependent upon the services of its employees, consultants and service providers. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. Principles of Consolidation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company and its wholly owned subsidiaries, Kiniksa Pharmaceuticals Corp. (“Kiniksa US”), Primatope Therapeutics, Inc. (“Primatope”) and Kiniksa Pharmaceuticals (UK), Ltd. (“Kiniksa UK”) as well as the subsidiaries of Kiniksa UK, Kiniksa Pharmaceuticals (Germany) GmbH (“Kiniksa Germany”) and Kiniksa Pharmaceuticals (France) SARL (“Kiniksa France”), after elimination of all significant intercompany accounts and transactions. In assessing the consolidation requirement for variable interest entities (“VIE”s), the Company focuses on identifying whether it has both the power to direct the activities that most significantly impact the VIE’s economic performance and the obligation to absorb losses or the right to receive benefits from the VIE. In the event that the Company is the primary beneficiary of a VIE, the assets, liabilities, and results of operations of the VIE would be included in the Company’s consolidated financial statements. At December 31, 2019 and 2018 and during the years then ended, the Company was not the primary beneficiary of a VIE. Use of Estimates The preparation of the Company’s consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the accrual for research and development expenses and the valuation of common shares and share‑based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates. Reporting and Functional Currency The financial results of the Company's global activities are reported in U.S. dollars (“USD”) and its foreign subsidiaries generally utilize their respective local currency to be their functional currency. Transactions in other currencies are recorded in the functional currency at the rate of exchange prevailing when the transactions occur. Monetary assets and liabilities denominated in other currencies are re-measured into the functional currency at the rate of exchange in effect at the balance sheet date. Exchange gains and losses arising from re-measurement of foreign currency-denominated monetary assets and liabilities are included in income in the period in which they occur. For our foreign subsidiaries where the local currency is the functional currency, assets and liabilities denominated in local currencies are translated into USD at end-of-period exchange rates and the resulting translation adjustments are reported as a component of accumulated other comprehensive income (loss) within shareholders' equity (deficit). Reverse Share Split On May 11, 2018, the Company effected a 1‑for‑2.73235 reverse share split of its authorized, designated, issued and outstanding common shares and preferred shares. Accordingly, all share and per share amounts for all periods presented in the accompanying consolidated financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this reverse share split. Initial Public Offering On May 23, 2018, the Company’s registration statement on Form S‑1 relating to its initial public offering of its Class A common shares (the “IPO”) was declared effective by the Securities and Exchange Commission (“SEC”). On May 29, 2018, the Company completed the IPO of 8,477,777 Class A common shares at $18.00 per share for gross proceeds of $152,600. In addition, on June 22, 2018, the Company completed the sale of 1,006,425 Class A common shares to the underwriters of the IPO following the exercise of their over‑allotment option to purchase additional shares at $18.00 per share for gross proceeds of $18,116. The aggregate net proceeds to the Company from the IPO, inclusive of the over‑allotment option exercise, was $155,536 after deducting underwriting discounts and commissions and other offering costs. Upon the closing of the IPO, all convertible preferred shares then outstanding automatically converted into 5,546,019 Class A common shares, 1,070,502 Class B common shares, 12,995,954 Class A1 common shares and 16,057,618 Class B1 common shares. In connection with the closing of the IPO, the Company amended and restated its bye‑laws (the “Amended & Restated Bye‑Laws”). Follow-on Offering and Private Placement On February 4, 2019, the Company completed a follow-on offering of 2,654,984 Class A common shares at a public offering price of $18.26 and a concurrent private placement of 2,000,000 Class A1 common shares at an offering price of $18.26 per share for aggregate gross proceeds of $85,000. In addition, on March 1, 2019, the Company completed the sale of 161,126 Class A common shares to the underwriters of the follow-on offering following the exercise in part of their over-allotment option to purchase additional shares at a public offering price of $18.26 per share for gross proceeds of $2,942. The aggregate net proceeds to the Company from the follow-on offering and concurrent private placement, inclusive of the over-allotment option exercise, was $82,988 after deducting underwriting discounts and commissions and other offering costs Liquidity In accordance with Accounting Standards Update (“ASU”) 2014‑15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205‑40), the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date the consolidated financial statements are issued. As of December 31, 2019, the Company had an accumulated deficit of $356,092. During the year ended December 31, 2019, the Company incurred a net loss of $161,867 and used $158,369 of cash in operating activities. The Company expects to continue to generate operating losses and cash used in operations for the foreseeable future. As of December 31, 2019, the Company had cash, cash equivalents and short‑term investments of $233,380. Based on its current operating plan, the Company expects that its cash, cash equivalents and short-term investments, will be sufficient to fund its operating expenses and capital expenditure requirements for at least twelve months from the issuance date of these consolidated financial statements. The future viability of the Company beyond that point is dependent on its ability to raise additional capital to finance its operations. The Company will need to finance its operations through public or private securities offerings, debt financings or other sources, which may include licensing, collaborations or other strategic transactions or arrangements. Although the Company has been successful in raising capital in the past, there is no assurance that it will be successful in obtaining such additional financing on terms acceptable to the Company, if at all. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate some or all of its research and development programs for product candidates, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects, or the Company may be unable to continue operations.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Cash and Cash Equivalents The Company classifies deposits in banks, money market funds and cash invested temporarily in various instruments with maturities of three months or less at the time of purchase as cash and cash equivalents. At December 31, 2019 and 2018, cash and cash equivalents consisted principally of U.S. Treasury notes, amounts held in money market accounts and cash on deposit at commercial banks. Short‑Term Investments The Company generally invests its excess cash in money market funds and short‑term investments in U.S. Treasury notes. Such investments included in short‑term investments on the Company’s consolidated balance sheets are considered available‑for‑sale debt securities and are reported at fair value with unrealized gains and losses included as a component of shareholders’ equity (deficit). Realized gains and losses, if any, on short‑term investments are included in interest income. The Company evaluates its short‑term investments with unrealized losses for other‑than‑temporary impairment. When assessing short‑term investments for other‑than‑temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary,” the Company reduces the investment to fair value through a charge to the consolidated statement of operations and comprehensive loss. No such adjustments were necessary during the periods presented. Concentrations of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk consist principally of cash, cash equivalents and short-term investments. At December 31, 2019 and 2018, substantially all of the Company’s cash, cash equivalents and short-term investments were held at two financial institutions. The Company generally maintains balances in various operating accounts at financial institutions that management believes to be of high credit quality, in amounts that may exceed federally insured limits. The Company has not experienced any losses related to its cash, cash equivalents and short-term investments and does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. Restricted Cash In conjunction with the Company’s lease agreement entered into in March 2018 (see Note 5), the Company maintains a letter of credit for the benefit of the landlord. As of December 31, 2019 and 2018, the underlying cash balance of $210 securing this letter of credit, was classified as non‑current in its consolidated balance sheet. Property and Equipment Property and equipment are recorded at cost and depreciated over the estimated useful lives of the related assets using the straight-line method. Maintenance and repairs are charged to expense as incurred. When assets are retired or otherwise disposed of, the cost of these assets and related accumulated depreciation or amortization are eliminated from the consolidated balance sheet and any resulting gains or losses are included in the consolidated statement of operations and comprehensive loss in the period of disposal. The expected useful lives of the respective assets are as follows: Estimated Useful Life Computer hardware and software 3 - 5 years Laboratory equipment 5 years Furniture, fixtures and vehicles 5 - 7 years Leasehold improvements Shorter of estimated useful life or lease term Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. To date, the Company has not recorded any impairment losses on long-lived assets. Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process common equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded as a reduction to the carrying value of convertible preferred shares or in shareholders’ equity (deficit) as a reduction of additional paid-in capital generated as a result of the offering. Should an in-process equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the consolidated statements of operations and comprehensive loss. As of December 31, 2018, the Company recorded deferred offering costs of $433 related to the follow-on offering of its Class A common shares and private placement of its Class A1 Common Shares. The follow-on offering and concurrent private placement were finalized in February 2019, and all prior deferred costs were recorded as a reduction to the carrying value. There were no deferred offering costs recorded as of December 31, 2019. Fair Value Measurements Certain assets and liabilities of the Company are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: · Level 1—Quoted prices in active markets for identical assets or liabilities. · Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. · Level 3—Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s restricted cash, which is held in a money market fund, is carried at fair value, determined based on Level 1 inputs in the fair value hierarchy described above (see Note 3). The Company’s cash equivalents and short-term investments, consisting of money market accounts and U.S. Treasury notes, are carried at fair value, determined based on Level 1 and 2 inputs in the fair value hierarchy described above (see Note 3). The carrying values of the Company’s prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values due to the short-term nature of these assets and liabilities. Leases In February 2016, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), which set forth the principles for recognition, measurement, presentation and disclosure of lease arrangements to enhance the transparency and comparability of financial reporting related to the arrangements. ASU 2016-02, including subsequently issued amendments, is collectively referred to as Accounting Standards Codification, Leases (Topic 842) (“ASC 842”). The Company adopted the new standard on January 1, 2019 using the modified retrospective transition approach as applied to leases existing as of the adoption date. The standard will be applied to all leases entered into after the initial adoption date. At the inception of an arrangement, the Company determines whether the arrangement is or contains a “lease” as defined by ASC 842. A lease is an arrangement, or part of an arrangement, that conveys the right to control the use of identified property, plant, or equipment (an identified asset) for a period of time in exchange for consideration. The Company determines if the arrangement conveys the right to control the use of an identified asset for a period of time. It assesses throughout the period of use whether the Company has both of the following (1) the right to obtain substantially all of the economic benefits from use of the identified asset and (2) the right to direct the use of the identified asset. This determination is reassessed if the terms of the arrangement are changed. Leases are classified as operating or finance leases based on the terms of the lease agreement and certain characteristics of the identified asset. Right-of-use (“ROU”) assets and lease liabilities are recognized at lease commencement date based on the present value of the minimum future lease payments. Most leases with a term greater than one year are recognized on the balance sheet as ROU assets with corresponding lease liabilities and, if applicable, long-term lease liabilities. The Company has elected not to recognize leases with a term of one year or less on its balance sheet. Operating leases, ROU assets and their corresponding lease liabilities are recorded based on the present value of lease payments over the expected remaining lease term. However, certain adjustments to the ROU assets may be required for items such as incentives received. The interest rate implicit in lease arrangements is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. In accordance with the guidance in ASU 2016-02, components of a lease should be split into three categories: lease components (e.g., land, building, etc.), non-lease components (e.g., common area maintenance, consumables, etc.), and non-components (e.g., property taxes, insurance, etc.); then the fixed and in-substance fixed contract consideration (including any related to non-components) must be allocated based on fair values to the lease components and non-lease components. Although separation of lease and non-lease components is required, certain practical expedients are available. Companies may elect the practical expedient to not separate lease and non-lease components. In which case, the Company would account for each lease component and the related non-lease component together as a single component. The Company has elected to account for the lease and non-lease components of each of its operating leases as a single lease component and allocate all of the arrangement consideration to the lease component only. The lease component results in an operating right-of-use asset being recorded on the balance sheet and amortized on a straight-line basis as lease expense. Segment Information The Company manages its operations as a single operating segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is on developing and delivering therapeutic medicines for patients suffering from debilitating diseases with significant unmet medical need. Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred to discover, research and develop drug candidates, including personnel expenses, share‑based compensation expense, allocated facility‑related and depreciation expenses, third‑party license fees and external costs of outside vendors engaged to conduct preclinical and clinical development activities and clinical trials as well as to manufacture clinical trial materials. Non‑refundable prepayments for goods or services that will be used or rendered for future research and development activities are recorded as prepaid expenses. Such amounts are recognized as an expense as the goods are delivered or the related services are performed, or until it is no longer expected that the goods will be delivered, or the services rendered. Milestone and other payments made to third-parties with respect to in-process research and development, in accordance with the Company’s license, acquisition and other similar agreements are expensed when determined to be probable and estimable. Research Contract Costs and Accruals The Company has entered into various research and development-related contracts with companies both inside and outside of the United States. The related costs are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research and development costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies or clinical trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ materially from the Company's estimates. The Company's historical accrual estimates have not been materially different from the actual costs. Patent Costs The Company charges patent-related costs in connection with filing and prosecuting patent applications to operations as incurred as their realization is uncertain. These costs are classified as general and administrative expenses. Share‑Based Compensation The Company measures all share-based awards granted to employees and directors based on their fair value on the date of the grant and recognizes compensation expense for those awards over the requisite service period. Forfeitures are accounted for as they occur. The Company issues share-based awards with both service-based vesting conditions and performance-based vesting conditions. Expense for awards with service-based vesting is recorded using the straight-line method, and expense for awards with performance-based vesting conditions is recognized using the accelerated-attribution method. For share-based awards granted to consultants and non-employees, compensation expense is recognized over the vesting period of the awards, which is generally the period during which services are rendered by such consultants and non-employees until completed. At the end of each financial reporting period prior to completion of the service, the fair value of these awards is remeasured using the then-current fair value of the Company's Class A common shares and updated assumption inputs in the Black-Scholes option-pricing model. The Company classifies share-based compensation expense in its consolidated statements of operations and comprehensive loss in the same manner in which the award recipient's payroll costs are classified or in which the award recipient's service payments are classified. The fair value of each restricted share award is estimated on the date of grant based on the fair value of the Company’s Class A common shares or Class B common shares on that same date. The fair value of each option grant is estimated on the date of grant using the Black-Scholes option-pricing model, which requires inputs based on certain subjective assumptions, including the expected share price volatility, the expected term of the award, the risk-free interest rate, and expected dividends (see Note 9). Prior to May 2018, the Company was a private company and, accordingly, lacks company-specific historical and implied volatility information for its shares. Therefore, it estimates its expected share price volatility based on the historical volatility of publicly traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded share price. The expected term of the Company’s options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The expected term of options granted to non-employees is equal to the contractual term of the option award. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends on common shares and does not expect to pay any cash dividends in the foreseeable future. The fair value of each restricted share unit award is based on the closing price of the Company’s Class A common shares on the date of grant. Restricted share unit awards with an associated performance condition are evaluated on a regular basis for probability of achievement, to determine the timing of recording share-based compensation expense in the Company’s consolidated statements of operations and comprehensive loss. Comprehensive Loss Comprehensive loss includes net loss as well as other changes in shareholders’ equity (deficit) that result from transactions and economic events other than those with shareholders. For the year ended December 31, 2019 and 2018, the Company’s other comprehensive loss was comprised of unrealized gain (loss) on short-term investments and currency translation adjustments, net of tax. Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the benefit for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. As an exempted company incorporated under the laws of Bermuda, the Company is principally subject to taxation in Bermuda. Under the current laws of Bermuda, tax on a company’s income is assessed at a zero percent tax rate. As a result, the Company has not recorded any income tax benefits from losses incurred in Bermuda during each reporting period, and no net operating loss carryforwards will be available to the Company for those losses. The Company’s wholly owned U.S. subsidiary, Kiniksa US, and Primatope are subject to federal and state income taxes in the United States. The Company’s wholly owned subsidiary Kiniksa UK., and its wholly owned subsidiaries, Kiniksa Germany and Kiniksa France are subject to taxation in their respective countries. The Company’s benefit for income taxes primarily relates to net credits earned against taxable income generated by its wholly owned subsidiaries, primarily, Kiniksa US, under cost‑plus arrangements that they have with the Company. The benefit for income taxes is impacted by the Foreign Derived Intangible Income, or (“FDII”), deduction and U.S. federal and state research and development tax credits. FDII was enacted as part of the tax reform enacted by the United States in December 2017, generally referred to as the U.S. Tax Cuts and Jobs Act with additional proposed regulations and guidance issued in 2019. Upon the completion of the Company’s assessment, the Company has included the tax impact of FDII in its income tax expense for the year ended December 31, 2019, based on its understanding of the rules available at the time of this filing. However, the amounts recorded could be impacted in the future when the proposed regulations and guidance are finalized. The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties. In 2019, the Company identified an uncertain tax position related to historic research and development credits as a result of a R&D study performed (see Note 11). Net Loss per Share The Company follows the two‑class method when computing net loss per share as the Company has issued shares that meet the definition of participating securities. The two‑class method determines net loss per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two‑class method requires income available to common shareholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. Basic net loss per share attributable to common shareholders is computed by dividing the net loss attributable to common shareholders by the weighted average number of common shares outstanding for the period. Diluted net loss attributable to common shareholders is computed by adjusting net loss attributable to common shareholders to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net loss per share attributable to common shareholders is computed by dividing the diluted net loss attributable to common shareholders by the weighted average number of common shares outstanding for the period, including potential dilutive common shares. For purpose of this calculation, outstanding options, unvested restricted common shares and convertible preferred shares are considered potential dilutive common shares. Recently Adopted Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued Account Standards Update (“ASU”), No. 2016-02, Leases (Topic 842) (“ASU 2016-02”) . The standard, including subsequently issued amendments, collectively referred to as Accounting Standards Codification (“ASC”) 842, established principles of recognition, measurement, presentation and disclosure of lease arrangements applicable to lessees and lessors in order to enhance the transparency and compatibility of financial reporting related to the arrangements, including with respect to the amount, timing and uncertainty of cash flows arising from a lease. The Company adopted new accounting guidance regarding the accounting for leases as of January 1, 2019 using a modified retrospective transition approach that was applied to leases existing as of, or entered into prior to, January 1, 2019. See Note 2, Summary of Significant Accounting Policies, “Leases” for a discussion of the Company’s policy with respect to this standard and Note 5, “Leases” for a discussion of the Company’s adoption of this standard and its impact on its consolidated financial statements and related disclosures. Upon the adoption of ASC 842, the Company recorded operating lease right-of-use assets of $3,682 and operating lease liabilities of $3,917 for its leases which were in effect and had commenced prior to January 1, 2019 and had original lease terms of more than 12 months. Recently Issued Accounting Pronouncements In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other— Internal-Use Software (Subtopic 350-40) (“ASU 2018-15”) , which amends ASC 350-40 to address a customer’s accounting for implementation costs incurred in a cloud computing arrangement (“CCA”) that is a service contract. ASU 2018-15 aligns the accounting for costs incurred to implement a CCA that is a service contract with the guidance on capitalizing costs associated with developing or obtaining internal-use software. Specifically, the ASU amends ASC 350 to include in its scope implementation costs of a CCA that is a service contract and clarifies that a customer should apply ASC 350-40 to determine which implementation costs should be capitalized in a CCA that is considered a service contract. The standard became effective for the Company beginning on January 1, 2020. The Company is currently evaluating the potential impact that ASC 350-40 may have on its consolidated financial statements and related disclosures . In June 2016, the FASB, issued ASU 2016-13, Financial Instruments: Credit Losses (Topic 326)(“ASU 2016-13)” , as clarified in ASU 2019-04 and ASU 2019-05. The objective of the standard is to provide information about expected credit losses on financial instruments at each reporting date and to change how other-than-temporary impairments on investment securities are recorded. The standard became effective for the Company beginning on January 1, 2020. The Company does not anticipate the adoption of this ASU to have a material impact on its consolidated financial statements and related disclosures. In December 2019, the FASB issued ASU 2019-12, Simplifying the Accounting for Income Taxes (Topic 740)(“ASU 2019-12”) . The objective of the standard is to improve areas of GAAP by removing certain exceptions permitted by ASC Topic 740 Income Taxes and clarifying existing guidance to facilitate consistent application. The standard will become effective for the Company beginning on January 1, 2021. The Company is currently evaluating the new standard to determine the potential impact of ASU 2019-12 on its consolidated financial statements and related disclosures.

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	12 Months Ended
	Dec. 31, 2019
Fair Value of Financial Assets and Liabilities
Fair Value of Financial Assets and Liabilities	3. Fair Value of Financial Assets and Liabilities Short‑term investments as of December 31, 2019 and 2018 consisted of U.S. Treasury notes all of which are due within six months. As of December 31, 2019 and 2018, the fair value of short‑term investments was $186,452 and $235,328, respectively. As of December 31, 2019, the amortized cost was $186,415 and gross unrealized gain was $37. As of December 31, 2018, the amortized cost was $235,332 and gross unrealized loss was $4. The following tables present information about the Company’s financial instruments measured at fair value on a recurring basis and indicate the level of the fair value hierarchy used to determine such fair values: Fair Value Measurements as of December 31, 2019 Using: Level 1 Level 2 Level 3 Total Assets: Restricted cash — money market funds $ 210 $ — $ — $ 210 Cash equivalents — money market funds 25,207 — — 25,207 Cash equivalents — U.S. Treasury notes — 10,192 — 10,192 Short-term investments — U.S. Treasury notes — 186,452 — 186,452 $ 25,417 $ 196,644 $ — $ 222,061 Fair Value Measurements as of December 31, 2018 Using: Level 1 Level 2 Level 3 Total Assets: Restricted cash — money market funds $ 210 $ — $ — $ 210 Cash equivalents — money market funds 29,721 — — 29,721 Cash equivalents — U.S. Treasury notes — 15,634 — 15,634 Short-term investments — U.S. Treasury notes — 235,328 — 235,328 $ 29,931 $ 250,962 $ — $ 280,893 During the years ended December 31, 2019 and 2018, there were no transfers between Level 1, Level 2 and Level 3. The money market funds were valued using quoted prices in active markets, which represent a Level 1 measurement in the fair value hierarchy. The Company’s cash equivalents and short-term investments as of December 31, 2019 and 2018 consisted of U.S. Treasury notes, which are not traded on a daily basis and, therefore, represent a Level 2 measurement in the fair value hierarchy at each period end.

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2019
Property and Equipment, Net
Property and Equipment, Net	4. Property and Equipment, Net Property and equipment, net consisted of the following: December 31, December 31, 2019 2018 Furniture, fixtures and vehicles $ 47 $ 91 Computer hardware and software 344 249 Leasehold improvements 3,627 2,676 Lab equipment 4,685 3,107 Construction in progress 20 552 Total property and equipment 8,723 6,675 Less: Accumulated depreciation (2,325) (319) Total property and equipment, net $ 6,398 $ 6,356 As of December 31, 2019, construction in progress is primarily comprised of lab equipment which the Company anticipates will be placed into service in 2020. Depreciation expense for the years ended December 31, 2019 and 2018 was $2,068 and $286, respectively.

Leases

Leases	12 Months Ended
	Dec. 31, 2019
Leases
Leases	5. Leases Kiniksa US leases office and laboratory space under operating leases. Leases with an initial term of 12 months or less are not recorded on the balance sheet; the Company recognizes lease expense for these leases on a straight-line basis over the lease term. For lease agreements entered into or reassessed after the Company’s adoption of ASC 842, the Company will combine lease and non-lease components. Kiniksa US’s leases have remaining lease terms of less than 2 years. On July 24, 2015, Kiniksa US entered into an operating lease in Wellesley Hills, Massachusetts for office space that comprised the former headquarters for Kiniksa US. In March 2016, effective August 1, 2016, Kiniksa US entered into an expansion and extension on its lease, which expanded its leased space to a total of 10,800 square feet. On March 31, 2017, Kiniksa US renewed this lease and extended the lease term to August 2018. Monthly lease payments, inclusive of base rent and ancillary charges, were $27. On March 13, 2018, Kiniksa US entered into an operating lease in Lexington, Massachusetts for office and laboratory space that comprises the new headquarters for Kiniksa US and on June 26, 2018, Kiniksa US entered into an amendment to the lease expanding the rentable space to a total of 27,244 square feet. On November 7, 2018, Kiniksa US entered into an amendment (the “Third Amendment”) to the lease expanding the rentable space to a total of 55,924 square feet which were occupied in phases through December 2019. The lease expires on July 31, 2021. Monthly lease payments include base rent, as well as, ancillary charges such as the share of operating expenses and real estate taxes. Base rent under the Third Amendment is $138 per month as of December 2019. On December 21, 2018, Kiniksa US entered into an operating lease in San Diego, California for office space comprising a total of 4,400 square feet. The lease commenced on January 1, 2019 and expires on December 31, 2020. Monthly lease payments for base rent are $13. Additional fees for ancillary charges such as the share of operating expenses, parking and real estate taxes are not included in the base rent. The components of lease cost consisted of operating lease costs and variable lease costs were $1,443 and $152 for the year end ended December 31, 2019. As of December 31, 2019, the weighted-average lease term was 1.47 years and the discount rate was 7.16%. Maturities of operating leases liabilities were as follows: As of December 31, 2020 $ 1,821 2021 972 2022 — 2023 and thereafter — Total future minimum lease payments $ 2,793 Less imputed interest (141) Present value of lease liabilities $ 2,652 Prior to the adoption of the new lease accounting standard, undiscounted future minimum rents payable as of December 31, 2018 under non-cancelable leases with the initial term exceeding one year were as follows: As of December 31, 2019 $ 1,394 2020 1,821 2021 972 2022 and thereafter — Total future minimum lease payments $ 4,187

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2019
Accrued Expenses
Accrued Expenses	6. Accrued Expenses Accrued expenses consisted of the following: December 31, December 31, 2019 2018 Accrued research and development expenses $ 11,813 $ 9,656 Accrued employee compensation and benefits 7,089 5,678 Accrued legal and professional fees 1,087 994 Other 426 90 $ 20,415 $ 16,418

Convertible Preferred Shares

Convertible Preferred Shares	12 Months Ended
	Dec. 31, 2019
Convertible Preferred Shares
Convertible Preferred Shares	7. Convertible Preferred Shares As of December 31, 2017, the Company’s bye-laws, as amended and restated, designated 22,885,492 authorized shares to be issued as convertible preferred shares with a par value of $0.000273235 per share, of which 17,128,120 shares were further designated as Series A convertible preferred shares (the “Series A preferred shares”) and 5,757,372 shares were further designated as Series B convertible preferred shares (the "Series B preferred shares"). In February 2018, the Company’s bye-laws were further amended and restated to, among other things, effect an increase in the number of authorized convertible preferred shares with a par value of $0.000273235 per share to 35,670,093 shares, of which 12,784,601 shares were further designated as Series C convertible preferred shares (the "Series C preferred shares"). The holders of convertible preferred shares had liquidation rights in the event of a deemed liquidation that, in certain situations, was not solely within the control of the Company. Therefore, the Series A, Series B and Series C convertible preferred shares (collectively, the “Preferred Shares”) were classified outside of shareholders' equity. In October 2015, the Company issued and sold 8,028,809 Series A preferred shares at a price of $4.6707 per share (the “Series A Original Issue Price”) for proceeds of $37,398, net of issuance costs of $102. In September 2016, the Company issued and sold an additional 9,099,311 Series A preferred shares at a price of $4.6707 per share for proceeds of $42,499, net of issuance costs of $1. In March 2017, the Company issued and sold 5,757,372 Series B preferred shares at a price of $6.9475 per share (the “Series B Original Issue Price”) for proceeds of $39,873, net of issuance costs of $127. In February 2018, the Company issued and sold 12,784,601 Series C preferred shares at a price of $15.6438 per share (the “Series C Original Issue Price”) for proceeds of $190,822, net of issuance costs of $9,178. In May 2018, upon the completion of the Company’s IPO (which qualified as a “Qualified IPO” under the Company’s bye‑laws, as amended and restated), all of the outstanding Preferred Shares were converted into 5,546,019 Class A common shares, 1,070,502 Class B common shares, 12,995,954 Class A1 common shares and 16,057,618 Class B1 common shares in accordance with the Company’s bye‑laws, as amended and restated. In connection with the completion of its IPO in May 2018, the Company amended and restated its bye‑laws to, among other things, authorize the issuance of undesignated preferred shares. As of December 31, 2019, no preferred shares were designated or issued. Prior to the conversion to common shares, the holders of the Preferred Shares had the following rights and preferences: Voting The holders of Preferred Shares were entitled to vote, together with the holders of common shares, on all matters submitted to shareholders for a vote. The holders of Series A preferred shares were entitled to the number of votes per Series A preferred share equal to the number of whole Class B common shares into which the Series A preferred shares were convertible at the time of such vote (which is ten votes for each Class B common share). The holders of Series B preferred shares were entitled to the number of votes per Series B preferred share equal to the number of whole Class A common shares into which the Series B preferred shares were convertible at the time of such vote (which was one vote for each Class A common share). The holders of Series C preferred shares were entitled to the number of votes per Series C preferred share equal to the number of whole Class A common shares into which the Series C preferred shares were convertible at the time of such vote (which was one vote for each Class A common share). Except as provided by law or by the other provisions of the Company’s bye‑laws, holders of Preferred Shares voted together with the holders of common shares as a single class. The holders of Preferred Shares, voting together as a single class, were entitled to elect two directors of the Company. The holders of Preferred Shares, voting together with the holders of common shares as a single class, were entitled to elect the remaining directors of the Company, except for the one director that the holders of Class A common shares and Class B common shares, voting together as a single class were entitled to elect. Conversion Each Series A preferred share was convertible, at the option of the holder, at any time and from time to time, and without the payment of additional consideration by the holder thereof, in such manner as permitted by Bermuda law, into such number of fully paid and non‑assessable Class B common shares determined by dividing the Series A Original Issue Price by the Series A Conversion Price (as defined below) in effect at the time of conversion. Each Series B preferred share was convertible, at the option of the holder, at any time and from time to time, and without the payment of additional consideration by the holder thereof, in such manner as permitted by Bermuda law, into such number of fully paid and non‑assessable Class A common shares determined by dividing the Series B Original Issue Price by the Series B Conversion Price (as defined below) in effect at the time of conversion. Each Series C preferred share was convertible, at the option of the holder, at any time and from time to time, and without the payment of additional consideration by the holder thereof, in such manner as permitted by Bermuda law, into such number of fully paid and non‑assessable Class A common shares determined by dividing the Series C Original Issue Price by the Series C Conversion Price (as defined below) in effect at the time of conversion. At the time of the IPO, the Series A Original Issue Price and Series A Conversion Price were equal to $4.6707. The Series B Original Issue Price and Series B Conversion Price were equal to $6.9475, and the Series C Original Issue Price and Series C Conversion Price were equal to $15.6438. Therefore, each Series A preferred share was convertible into one Class B common share, each Series B preferred share was convertible into one Class A common share and each Series C preferred share was convertible into one Class A common share. Further, upon either (i) the closing of the sale of Class A common shares or Class B common shares to the public at a price of at least $15.6438 per share (subject to appropriate adjustment in the event of any share dividend, share split, combination or other similar recapitalization with respect to the applicable class of common shares) in an initial public offering resulting in at least $100,000 of gross proceeds to the Company (a “Qualified IPO”) or (ii) the date and time, or the occurrence of an event, specified by vote or written consent of the holders of a majority of the outstanding Preferred Shares, voting together as a single class on an as if converted to Class A common shares basis, all outstanding Series A preferred shares would automatically be converted, in such manner as permitted pursuant to Bermuda law, into Class B common shares at the then effective conversion rate, and all outstanding Series B and Series C preferred shares would automatically be converted, in such manner as permitted pursuant to Bermuda law, into Class A common shares at the then effective conversion rate. Notwithstanding the foregoing, in the event of a mandatory conversion of preferred shares as a result of a Qualified IPO, (a) holders of Series A preferred shares could elect to receive Class B1 common shares in lieu of Class B common shares and (b) holders of Series B and Series C preferred shares could elect to receive Class A1 common shares in lieu of Class A common shares. Dividends The holders of the Preferred Shares were entitled to receive noncumulative dividends when and if declared by the Company’s board of directors. The Company was not permitted to declare, pay or set aside any dividends on any other class or series of shares of the Company, other than dividends on common shares payable in common shares, unless the holders of the Preferred Share first received, or simultaneously received, a dividend on each outstanding Preferred Share equal to (i) in the case of a dividend on any class of common shares or any class or series convertible into common shares, that dividend per Preferred Share as would have equaled the product of (a) the dividend payable on each share of such class or series determined, if applicable, as if all shares of such class or series had been converted into common shares and (b) the number of common shares issuable upon conversion of a share of the applicable series of Preferred Shares, or (ii) in the case of a dividend on any class or series that was not convertible into common shares, at a rate per Preferred Share determined by (a) dividing the amount of the dividend payable on each share of such class or series of shares by the original issue price of such class or series (subject to appropriate adjustment in the event of any bonus share, share dividend, share split, combination of or other similar recapitalization with respect to such class or series) and (b) multiplying such fraction by an amount equal to the applicable Series A, Series B or Series C Original Issue Price. No cash dividends were declared or paid on the Preferred Shares. Liquidation Preference In the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company or deemed liquidation event (as defined below), the holders of Preferred Shares then outstanding were entitled to be paid out of the assets of the Company available for distribution to its shareholders, on a pari passu basis, before any payment was made to the holders of common shares by reason of their ownership thereof, an amount per share equal to the greater of (i) one times the applicable Original Issue Price, plus any dividends declared but unpaid thereon, and (ii) such amount per share as would have been payable had all Preferred Shares been converted into common shares immediately prior to such liquidation, dissolution, winding up or deemed liquidation event. Thereafter, the remaining assets of the Company available for distribution to its shareholders would have been distributed among the holders of common shares, pro rata based on the number of shares held by each such holder. If upon any such liquidation, dissolution or winding up of the Company or deemed liquidation event, the assets of the Company available for distribution to its shareholders were insufficient to pay the holders of Preferred Shares the full amount to which they were entitled, the holders of Preferred Shares would have shared ratably in any distribution of the assets available for distribution in proportion to the respective amounts which would otherwise have been payable in respect of the shares held by such holders of Preferred Shares upon such distribution if all amounts payable on or with respect to such shares were paid in full. Unless a majority of the holders of the then outstanding Preferred Shares elected otherwise, a deemed liquidation event would include a merger or consolidation (other than one in which shareholders of the Company own a majority by voting power of the outstanding shares of the surviving or acquiring company or corporation) or a sale, lease, transfer, exclusive license or other disposition of all or substantially all of the assets of the Company. Redemption The Company’s bye‑laws, as amended and restated, did not provide redemption rights to the holders of Preferred Shares.

Common Shares

Common Shares	12 Months Ended
	Dec. 31, 2019
Common Shares
Common Shares	8. Common Shares As of December 31, 2017, the Company’s bye‑laws, as amended and restated, authorized the Company to issue 43,918,239 total shares with a par value of $0.000273235, of which 5,507,938 and 3,568,353 shares were designated as Class A and Class B common shares, respectively. In February 2018, the Company’s bye‑laws were further amended and restated to, among other things, effect an increase in the number of authorized common shares to 44,746,463 shares, of which 5,507,938 shares were designated as Class A common shares and 3,568,353 shares were designated as Class B common shares. The remaining 11,956,456 shares that were not designated as common shares or Preferred Shares as of December 31, 2017 could have been designated to any class at any time in the future by the Company’s board of directors. No Class A1 common shares or Class B1 common shares were designated as of December 31, 2017. On May 23, 2018, the Company’s registration statement on Form S‑1 relating to the IPO was declared effective by the SEC. On May 29, 2018, the Company completed the IPO of 8,477,777 Class A common shares at a public offering price of $18.00 per share for gross proceeds of $152,600. In addition, on June 22, 2018, the Company completed the sale of 1,006,425 Class A common shares to the underwriters of the IPO following the exercise in part of their over‑allotment option to purchase additional shares at a public offering price of $18.00 per share for gross proceeds of $18,116. The aggregate net proceeds to the Company from the IPO, inclusive of the over‑allotment option exercise, was $155,536 after deducting underwriting discounts and commissions and other offering costs. In May 2018, upon completion of the IPO (which qualified as a “Qualified IPO” under the Company’s bye ‑laws, as amended and restated), all outstanding Preferred Shares were converted into 5,546,019 Class A common shares, 1,070,502 Class B common shares, 12,995,954 Class A1 common shares and 16,057,618 Class B1 common shares in accordance with the Company’s bye‑laws, as amended and restated. In connection with the completion of the IPO in May 2018, the Company increased the authorized capital of the Company to $54,647 consisting of 200,000,000 shares of $0.000273235 par value per share and, among other things, amended the description of different classes of shares under the Amended & Restated Bye‑Laws. On February 4, 2019, the Company completed a follow-on offering of 2,654,984 Class A common shares at a public offering price of $18.26 and a concurrent private placement of 2,000,000 Class A1 common shares at an offering price of $18.26 per share for aggregate gross proceeds of $85,000. In addition, on March 1, 2019, the Company completed the sale of 161,126 Class A common shares to the underwriters of the follow-on offering following the exercise in part of their over-allotment option to purchase additional shares at a public offering price of $18.26 per share for gross proceeds of $2,942. The aggregate net proceeds to the Company from the follow-on offering and concurrent private placement, inclusive of the over-allotment option exercise, was $82,988 after deducting underwriting discounts and commissions and other offering costs. The rights of the holders of the Company’s Class A common shares, Class B common shares, Class A1 common shares and Class B1 common shares are identical, except with respect to voting, transferability and conversion, as described below. As of December 31, 2017, the voting, dividend and liquidation rights of the holders of the Company’s common shares were subject to and qualified by the rights, powers and preferences of the holders of the Preferred Shares as set forth above. In May 2018, following the conversion of the Preferred Shares into common shares, the voting, dividend and liquidation rights of the holders of the Company’s common shares were then subject to and qualified by the rights, powers and preferences of the holders of the preferred shares, if any. As of December 31, 2019, no preferred shares were designated or issued. Voting Each Class A common share entitles the holder to one vote on all matters submitted to the shareholders for a vote. Each Class B common share entitles the holder to ten votes on all matters submitted to the shareholders for a vote. Holders of Class A1 common shares and Class B1 common shares have no voting rights. As of December 31, 2017, the holders of the Class A and Class B common shares, voting together as a single class, were entitled to elect one director of the Company. The holders of the Class A and Class B common shares, voting together with the holders of the Preferred Shares, voting together as a single class, were entitled to elect the remaining directors of the Company, except for the two directors of the Company that the holders of the Preferred Shares, voting together as a single class, were entitled to elect. In May 2018, following the conversion of the Preferred Shares into common shares, the holders of Class A and Class B common shares, voting together as a single class, are entitled to elect the directors of the Company. Dividends Common shareholders are entitled to receive dividends, as may be declared by the Company’s board of directors. As of December 31, 2017, any such dividends would have been subject to the preferential dividend rights of the holders of the Preferred Shares. In May 2018, following the conversion of the Preferred Shares into common shares, any such dividends would be subject to the rights, powers and preferences of the preferred shares, if any. As of December 31, 2019, no preferred shares were designated or issued. Through December 31, 2019, no cash dividends have been declared or paid. Conversion Each Class B common share shall automatically convert into one Class A common share upon certain transfers of such shares by the holder thereof (subject to certain exceptions). Each Class B common share is convertible, at the holder’s election into one Class A common share or one Class B1 common share. Each Class A1 common share is convertible into one Class A common share at the holder’s election (subject to certain exceptions). Each Class B1 common share shall automatically convert into one Class A common share upon certain transfers of such shares by the holder thereof (subject to certain exceptions). Each Class B1 common share is convertible into one Class A common share or one Class B common share at the holder’s election (subject to certain exceptions). There are no conversion rights associated with the Class A common shares.

Share Based Compensation

Share Based Compensation	12 Months Ended
	Dec. 31, 2019
Share-Based Compensation
Share-Based Compensation	9. Share‑Based Compensation 2018 Incentive Award Plan In May 2018, the Company’s board of directors and shareholders approved the 2018 Incentive Award Plan (the “2018 Plan”), which became effective on May 23, 2018. The 2018 plan provides for the grant of incentive options, nonqualified options, share appreciation rights, restricted shares, dividend equivalents, restricted share units and other share- or cash- based awards. Upon the effectiveness of the 2018 Plan, the Company ceased granting awards under its 2015 Equity Incentive Plan (as amended, the “2015 Plan” together with the 2018 Plan, the “Plans”). A total of 4,466,500 Class A common shares were initially reserved for issuance under the 2018 Plan. The number of Class A common shares that may be issued under the 2018 Plan will automatically increase on each January 1, beginning in 2019 and continuing for each fiscal year until, and including, the fiscal year ending December 31, 2028, equal to the lesser of (i) 4% of the Class A common shares outstanding (on an as‑converted basis) on the final day of the immediately preceding calendar year and (ii) a smaller number of Class A common shares determined by the Company’s board of directors. In 2019, the board of directors approved an increase of 1,979,586 shares, equal to 4% of the as-converted Class A common shares outstanding on December 31, 2018. No more than 27,915,000 Class A common shares may be issued under the 2018 Plan upon the exercise of incentive options. The Class A common shares underlying any awards issued under the 2018 Plan or the 2015 Plan that on or after the effective date of the 2018 Plan expire, lapse unexercised or are terminated, exchanged for cash, surrendered, repurchased, canceled without having been fully exercised or forfeited under the 2018 Plan or the 2015 Plan will be added back to the Class A common shares available for issuance under the 2018 Plan. As of December 31, 2019, 2,145,907 shares remained available for future grant. Rilonacept Long-Term Incentive Plan In December 2019, the compensation committee of the Company’s board of directors approved the Company’s Rilonacept Long-Term Incentive Plan (“RLTIP”) under the Company’s 2018 Plan to incentivize eligible employees of the Company or any of its subsidiaries to achieve U.S. Food and Drug Administration (“FDA”) approval for the commercial sale and marketing of rilonacept for the treatment of recurrent pericarditis in the United States (“RLTIP Milestone”). The RLTIP provides for the potential to receive a cash award and two grants of restricted share unit (“RSU”) awards covering Class A common shares under the 2018 Plan. The target award value for each of the cash award and the two RSU awards will be equal to one-third of a participant’s annual target bonus for the year of grant, as determined in accordance with the RLTIP. Depending on the date-range within which the RLTIP Milestone is achieved (such date the “Achievement Date”) occurs, the RLTIP provides for (i) an earnout percentage that can be achieved as to 100%, 50%, 25% or 0% and (ii) an upside earnout percentage that can be achieved as to 50%, 25% or 0%. No awards will be earned or vest, and the second RSU award will not be granted, in the event the Achievement Date does not occur by a specified date. The cash award is eligible to be earned and vested upon the Achievement Date with respect to an amount determined in accordance with the RLTIP based on the earnout percentage. The number of Class A common shares issuable under the first RSU award (“First RSU Award”) as a result of the RLTIP Milestone will be determined in accordance with the RLTIP based on the earnout percentage, and such RSUs will vest on the first anniversary of the Achievement Date, subject to continued employment on such date. The second RSU award will be granted on the Achievement Date with respect to a number of shares determined in accordance with the RLTIP, based on both the earnout percentage and the upside earnout percentage, and will vest on the second anniversary of the Achievement Date, subject to continued employment through such date. 2015 Equity Incentive Plan Until May 23, 2018 (the effective date of the 2018 Plan), the 2015 Plan provided for the Company to grant qualified incentive options, nonqualified options, share grants and other share‑based awards to employees and non‑employees to purchase the Company’s Class A common shares. On the effective date of the 2018 Plan, the Company ceased granting awards under the 2015 Plan. At that time, the 4,691,213 shares of Class A common shares subject to outstanding awards under the 2015 Plan remained reserved for issuance under the plan pursuant such awards and the 92,170 Class A common shares that had been available for future grant under the 2015 Plan were no longer authorized and reserved for issuance or available for future grant under the 2015 Plan. As of December 31, 2019, there were 4,125,923 shares of Class A common shares subject to outstanding awards under the 2015 Plan and reserved for issuance under the 2015 Plan pursuant such awards. On May 23, 2018, the effective date of the 2018 Plan, the Company ceased granting awards under the 2015 Plan and no Class A common shares were available for future grant under the 2015 Plan in connection with the 2018 Plan becoming effective. The exercise price for incentive options was determined by the Company’s board of directors. All incentive options granted to any person possessing 10% or less of the total combined voting power of all classes of shares could not have an exercise price of less than 100% of the fair market value of the Class A common shares on the grant date. All incentive options granted to any person possessing more than 10% of the total combined voting power of all classes of shares could not have an exercise price of less than 110% of the fair market value of the Class A common shares on the grant date. The option term for incentive awards could not be greater than 10 years. Incentive options granted to persons possessing more than 10% of the total combined voting power of all classes of shares could not have an option term of greater than five years. The vesting period for equity‑based awards was determined by the board of directors, which was generally four to six years. For awards granted to employees and non‑employees with four‑year vesting terms, 25% of the option vests on the first anniversary of the grant date and the remaining shares vest equally each month for three years thereafter. For awards granted to employees with six‑year vesting terms, 16% of the option vests on the first anniversary of the grant date and the remaining shares vest based on a predetermined vesting schedule for five years thereafter. Shares that are expired, terminated, surrendered or canceled under the 2015 Plan without having been fully exercised become be available for future awards under the 2018 Plan. Share Option Grants During the Years Ended December 31, 2019 and 2018 During the years ended December 31, 2019 and 2018, the Company granted options to purchase 3,605,388 and 3,114,139 Class A common shares, respectively, to employees and directors. The Company recorded share‑based compensation expense for options granted to employees and directors of $13,322 and $5,464 during the years ended December 31, 2019 and 2018, respectively. During the years ended December 31, 2019 and 2018, the Company granted options to purchase 3,200 and 4,000 Class A common shares, respectively, to non‑employees. The Company recorded share‑based compensation expense for options granted to non‑employees of $94 and $130 during the years ended December 31, 2019 and 2018, respectively. 2018 Employee Share Purchase Plan In May 2018, the Company’s board of directors and shareholders approved the 2018 Employee Share Purchase Plan (the “2018 ESPP”), which became effective on May 23, 2018. A total of 670,000 Class A common shares were initially reserved for issuance under the 2018 ESPP. The number of Class A common shares that may be issued under the 2018 ESPP will automatically increase on each January 1, beginning in 2019 and continuing for each fiscal year until, and including, the fiscal year ending December 31, 2028, equal to the lesser of (i) 1% of the Class A common shares outstanding (on an as‑converted basis) on the final day of the immediately preceding calendar year and (ii) a smaller number of Class A common shares determined by the Company’s board of directors, provided that no more than 6,420,000 Class A common shares may be issued under the 2018 ESPP. As of December 31, 2019, 598,334 Class A common shares were available for future issuance under the 2018 ESPP. In December 2019, the Company’s board of directors determined that the January 1, 2020 automatic increase in shares available under the 2018 ESPP would be zero shares. Option Valuation The assumptions that the Company used to determine the grant‑date fair value of options granted to employees and directors under the 2015 Plan and the 2018 Plan (collectively, the “Plans”) during the years ended December 31, 2019 and 2018 were as follows, presented on a weighted‑average basis: Years Ended December 31, 2019 2018 Risk-free interest rate 2.07 % 2.82 % Expected term (in years) 6.22 6.40 Expected volatility 79.14 % 75.04 % Expected dividend yield % % The assumptions that the Company used to determine the fair value of options granted to non-employees were as follows, presented on a weighted-average basis: Years Ended December 31, 2019 2018 Risk-free interest rate 1.38 % 2.91 % Expected term (in years) 2.77 7.35 Expected volatility 68.17 % 74.18 % Expected dividend yield % % Options Through December 31, 2017, all options granted by the Company under the 2015 Plan were for the purchase of Class A common shares. Until May 23, 2018 (the effective date of the 2018 Plan), the 2015 Plan provided for the Company to grant qualified incentive share options, nonqualified share options, share grants and other share‑based awards to employees, directors, and consultants to purchase the Company’s Class A common shares. On May 23, 2018, the Company ceased granting awards under the 2015 Plan. At that time, shares of Class A common shares subject to outstanding awards under the 2015 Plan remained reserved for issuance under the plan pursuant such awards and shares of Class A common shares that had been available for future grant under the 2015 Plan were no longer authorized and reserved for issuance or available for future grant under the 2015 Plan. However, the 2015 Plan continues to govern the terms and conditions of the outstanding awards granted under it. Class A common shares subject to awards granted under the 2015 Plan that are forfeited, lapse unexercised or are settled in cash become available for issuance under the 2018 Plan. The following table summarizes option activity for the year ended December 31, 2019: Weighted Weighted Average Average Remaining Aggregate Number of Exercise Contractual Intrinsic Shares Price Term Value (in years) Outstanding as of December 31, 2018 5,960,939 $ 10.25 8.56 $ 108,352 Granted 3,608,588 $ 13.44 Exercised (150,253) $ 3.93 Forfeited (927,540) $ 15.26 Outstanding as of December 31, 2019 8,491,734 $ 11.17 7.88 $ 27,217 Options exercisable as of December 31, 2019 3,373,659 $ 7.29 6.24 $ 19,903 Options unvested as of December 31, 2019 5,118,075 $ 13.74 8.96 $ 7,314 The aggregate intrinsic value of options is calculated as the difference between the exercise price of the options and the fair value of the Company’s common shares for those options that had exercise prices lower than the fair value of the Company’s common shares. During the year ended December 31, 2019, option holders exercised 150,253 options for Class A common shares with an intrinsic value of $1,776 for total cash proceeds to the Company of $590. During the year ended December 31, 2018, option holders exercised 25,683 options for Class A common shares with an intrinsic value of $411 for total cash proceeds to the Company of $87. The weighted-average grant-date fair value per share of options granted during the years ended December 31, 2019 and 2018 was $9.36 and $11.96, respectively. The total fair value of options vested during the years ended December 31, 2019 and 2018 was $13,997 and $2,255, respectively. Restricted Shares Under terms of the Class A and Class B restricted share agreements covering the Class A and Class B common shares, the restricted shares vest over a four‑year period during which time the Company has the right to repurchase up to all unvested shares at the amount paid if the relationship between the recipient and the Company ceases. Subject to the continued employment (or other engagement of the recipient by the Company as described in the restricted share agreements), all of the restricted common shares became fully vested within four years of the date of issuance. The following table summarizes restricted share activity for the year ended December 31, 2019: Class A Class B Weighted Weighted Average Average Number of Grant Date Number of Grant Date Shares Fair Value Shares Fair Value Unvested restricted shares outstanding as of December 31, 2018 133,812 $ 0.000273235 743,407 $ 0.000273235 Granted — — — — Vested (133,812) $ 0.000273235 (743,407) $ 0.000273235 Unvested restricted shares outstanding as of December 31, 2019 — — — — The aggregate fair value of restricted shares that vested during the years ended December 31, 2019 and 2018 was $12,154 and $15,182, respectively. Restricted Share Units An RSU represents the right to receive one share of the Company’s Class A common share upon vesting of the RSU. The fair value of each RSU is based on the closing price of the Company’s Class A common shares on the date of grant. In December 2019, the Company granted RSUs with service conditions that vest in one installment provided that the recipient remains employed with the Company (“Time-Based RSUs”) through December 31, 2020. During the year ended December 31, 2019, the Company also granted the First RSU Award as part of the RLTIP, which becomes eligible to vest upon the Achievement Date and will vest upon the first anniversary of such date, subject to the recipient’s continued employment through that date. In the event the RLTIP Milestone is not achieved, none of the First RSU Award will vest. The grant-date fair value of the Time-Based RSUs granted in 2019 was $1,250 and will be recognized on a straight-line basis through the vest date for these shares. For the year ended December 31, 2019, the Company recognized $65 in Time-Based RSU expense. The grant-date fair value of the First RSU Award was $2,994 and will be recognized when the RLTIP Milestone is deemed probable of achievement through the date the First RSU Award will vest. During the year ended December 31, 2019, the Company did not recognize compensation expense related to the First RSU Award, as achievement of the RLTIP Milestone was determined to be not probable. The following table summarizes RSU activity for the year ended December 31, 2019: Weighted Average Number of Grant Date Shares Fair Value Unvested RSUs as of December 31, 2018 — $ — Granted 328,296 $ 12.93 Vested — $ — Forfeited — $ — Unvested RSUs as of December 31, 2019 328,296 $ 12.93 Share-Based Compensation Share‑based compensation expense was classified in the consolidated statements of operations and comprehensive loss as follows: Years Ended December 31, 2019 2018 Research and development expenses $ 5,746 $ 2,285 General and administrative expenses 9,334 3,416 $ 15,080 $ 5,701 As of December 31, 2019, total unrecognized compensation cost related to the unvested option-based awards was $44,185, which is expected to be recognized over a weighted average remaining period of 3.1 years. As of December 31, 2019, total unrecognized compensation cost related to the unvested Time-Based RSUs was $1,185, which is expected to be recognized over a weighted average remaining period of 1.0 year. As of December 31, 2019, total unrecognized compensation cost related to the First RSU Award was $2,994, which will be recognized when the RLTIP Milestone is deemed probable of achievement through the date the First RSU Award vests .

License and Acquisition Agreeme

License and Acquisition Agreements	12 Months Ended
	Dec. 31, 2019
License and Acquisition Agreements
License and Acquisition Agreements	10. License and Acquisition Agreements Biogen Asset Purchase Agreement In September 2016, the Company entered into an asset purchase agreement (the “Biogen Agreement”) with Biogen MA Inc. (“Biogen”) to acquire all of Biogen’s right, title and interest in and to certain assets used in or relating to KPL‑716 and other antibodies covered by certain patent rights, including patents and other intellectual property rights, clinical data, know‑how, and clinical drug supply. In addition, Biogen granted to the Company a non‑exclusive, sublicensable, worldwide license to certain background patent rights related to the KPL‑716 program. The Company is obligated to use commercially reasonable efforts to develop and commercialize such acquired products. In exchange for these rights, the Company made an upfront payment to Biogen of $11,500 and a technology transfer payment of $500. The Company accounted for the acquisition of technology as an asset acquisition because it did not meet the definition of a business. The Company recorded the upfront payment and technology transfer payment as research and development expense in the consolidated statement of operations and comprehensive loss because the acquired technology represented in‑process research and development and had no alternative future use. Under the Biogen Agreement, the Company is obligated to make milestone payments to Biogen of up to $179,000 upon the achievement of specified clinical and regulatory milestones in multiple indications in various territories, including milestone payments of $4,000 and $10,000 paid during the year ended December 31, 2017 and the year ended December 31, 2019, respectively, each payment was associated with the achievement of a specified clinical milestone event. Additionally, the Company could be obligated to make up to an aggregate of up to $150,000 of payments upon the achievement of specified annual net sales milestones and to pay tiered royalties on escalating tiers of annual net sales of licensed products starting in the high single‑digit percentages and ending below the teens. The Company also agreed to pay certain obligations under third‑party contracts retained by Biogen that relate to the KPL‑716 program. Under these retained contracts, the Company paid a one‑time upfront sublicense fee of $150 and is obligated to pay insignificant annual maintenance fees as well as clinical and regulatory milestone payments of up to an aggregate of $1,575. The Company made insignificant payments in connection with the retained contracts during the years ended December 31, 2019 and 2018. The Biogen Agreement will terminate upon the expiration of all payment obligations with respect to the last product in all countries in the territory. The Company has the right to terminate the agreement with 90 days’ prior written notice. Both parties may terminate by mutual written consent or in the event of material breach of the agreement by the other party that remains uncured for 90 days (or 30 days for payment‑related breaches). During the year ended December 31, 2019, the Company recorded research and development expense of $10,347 primarily related to milestone payments associated with the achievement of a specified clinical milestone event as well as other payments in connection with the retained contracts due under the Biogen Agreement. The Company did not incur any research and development expense, other than insignificant payments in connection with the retained contracts, under the Biogen Agreement during the year ended December 31, 2018 Novo Nordisk License Agreement In August 2017, the Company entered into a license agreement (the “Novo Nordisk Agreement”) with Novo Nordisk A/S (“Novo Nordisk”), pursuant to which the Company was granted an exclusive, sublicensable, worldwide license under certain intellectual property rights controlled by Novo Nordisk to make, use, develop and commercialize KPL‑045 for all indications. In consideration for the license, the Company made an upfront payment of $1,500 to Novo Nordisk. The Company accounted for the acquisition of technology as an asset acquisition because it did not meet the definition of a business. The Company recorded the upfront payment as research and development expense in the consolidated statement of operations and comprehensive loss because the acquired technology represented in‑process research and development and had no alternative future use. In January 2020, the Company terminated the Novo Nordisk Agreement in accordance with the terms and conditions of the agreement. Under the Novo Nordisk Agreement, the Company was required to make a payment of $150 upon completion of the technology transfer by Novo Nordisk. The technology was transferred during the year ended December 31, 2018 and, as a result, this payment was made and was recorded in the Company’s consolidated statement of operations for the year ended December 31, 2018. In addition, the Company was obligated to make milestone payments upon the achievement of specified clinical, regulatory and initial sales milestones and upon the achievement of annual net sales thresholds including a payment of $1,000 upon the earlier to occur of a specified regulatory milestone and January 2020, unless the Novo Nordisk Agreement is earlier terminated by either party. As of December 31, 2019 and December 31, 2018, the Company determined that the payment related to the milestone was not probable and, therefore, no amount was recorded in the Company’s consolidated statement of operations and comprehensive loss during years ended December 31, 2019 and 2018. Under the Novo Nordisk Agreement, the Company was solely responsible for all development, regulatory and commercial activities and costs. The Company is also responsible for costs related to filing, prosecuting and maintaining the licensed patent rights. The Company did not record any research and development expense during the year ended December 31, 2019 in connection with milestone payments due under the Novo Nordisk Agreement. During the year ended December 31, 2018, the Company recorded research and development expense of $154, in connection with milestone payments due under the Novo Nordisk Agreement. Primatope Stock Purchase Option Agreement In September 2017, the Company entered into a stock purchase option agreement (the “Primatope Agreement”) with Primatope Therapeutics, Inc. (“Primatope”), pursuant to which the Company was granted a license to certain intellectual property rights owned or controlled by Primatope to research, develop, and manufacture the preclinical antibody, KPL‑404. The agreement provided the Company with an exclusive call option to purchase 100% of the equity securities of Primatope. Upon execution of the agreement, the Company made $500 in upfront payments for the initial option period through April 2018 (the “Initial Option Period”). The Primatope Agreement allowed for up to three extensions of the Initial Option Period through January 2019 (including the initial option period, the “Option Period”) for total extension payments of up to $800. Through December 31, 2018, the Company made payments totaling $800 to extend the Option Period to January 15, 2019. During the Option Period, the Company could conduct research and preclinical work to assess the viability of the asset. The Company determined that the call option represented a variable interest in Primatope and that Primatope is a VIE. However, as the Company had no ability to control the board of directors or direct the ongoing activities of Primatope during the Option Period, the Company did not have power over the activities that most significantly impact Primatope’s economic performance and was not the primary beneficiary of Primatope. As a result, the Company did not consolidate the assets, liabilities, and results of operations of Primatope. In January 2019, the Company exercised the call option and in March 2019, the Company acquired all of the issued and outstanding equity securities of Primatope (the “Primatope Acquisition”) in exchange for $18,000 comprised of upfront consideration of $10,000 at closing and milestone payments of $5,000,which had been achieved as of the closing date, and in June 2019, the Company made the final milestone payment of $3,000, which was achieved during the year ended December 31, 2019 following the closing, each paid in a combination of cash and Class A common shares (inclusive of escrow and holdback amounts) in accordance with the Primatope Agreement. At the closing of the Primatope Acquisition, Primatope became a wholly owned subsidiary of the Company and the acquisition was accounted for as an asset acquisition as it did not meet the definition of a business. The Company recorded the upfront payment and milestone payments as research and development expense in the consolidated statement of operations and comprehensive loss because the acquired technology represented in‑process research and development and had no alternative future use. During the year ended December 31, 2019, the Company did not incur any research and development expense directly in connection with milestone or other payments related to the Primatope Acquisition or the Primatope Agreement. During the year ended December 31, 2019, the Company recorded research and development expense of $18,000 related to the Primatope Acquisition. During the year ended December 31, 2018, the Company recorded research and development expense of $800, related to the extension of the option period under the Primatope Agreement. Beth Israel Deaconess Medical Center License Agreement As a result of the Primatope Acquisition, the Company acquired the rights to an exclusive license to certain intellectual property rights controlled by Beth Israel Deaconess Medical Center, Inc. (“BIDMC”) to make, use, develop and commercialize KPL-404 (the “BIDMC Agreement”). Under the BIDMC Agreement, the Company is solely responsible for all development, regulatory and commercial activities and costs. The Company is also responsible for costs related to filing, prosecuting and maintaining the licensed patent rights. Under the BIDMC Agreement, the Company is obligated to pay an insignificant annual maintenance fee as well as clinical and regulatory milestone payments of up to an aggregate of $1,200 to BIDMC. The Company is also obligated to pay a low single-digit royalty on annual net sales of products licensed under the agreement. During the year ended December 31, 2019, the Company recorded research and development expense of $10 in connection with the BIDMC Agreement. Regeneron License Agreement In September 2017, the Company entered into a license agreement (the “Regeneron Agreement”) with Regeneron Pharmaceuticals, Inc. (“Regeneron”), pursuant to which the Company has been granted an exclusive, sublicensable license under certain intellectual property rights controlled by Regeneron to develop and commercialize rilonacept in certain fields and territories. The Company is obligated to use commercially reasonable efforts to develop and commercialize such licensed products. In exchange for these rights, the Company made an upfront payment of $5,000. The Company accounted for the acquisition of technology as an asset acquisition because it did not meet the definition of a business. The Company recorded the upfront payment as research and development expense in the consolidated statement of operations and comprehensive loss because the acquired technology represented in‑process research and development and had no alternative future use. Under the Regeneron Agreement, the Company is also obligated to make payments to Regeneron of up to an aggregate of $27,500 upon the achievement of specified regulatory milestones. Upon commercialization of the licensed products, the parties will share profits equally for all commercial products, after deducting certain commercialization expenses subject to specified limits. Under the Regeneron Agreement, the Company is solely responsible for all development and commercialization activities and costs in its territories. The Company is also responsible for costs related to the filing, prosecution and maintenance of certain licensed patent rights. The parties also entered into a clinical supply agreement under which Regeneron agreed to manufacture the developed product during the clinical phase. During the years ended December 31, 2019 and 2018, the Company recorded research and development expense of $6,854 and $1,835, respectively, related to the purchase of drug materials under this agreement. As of December 31, 2019, the Company has non‑cancelable purchase commitments under the clinical supply agreement (see Note 13). The Regeneron Agreement will expire when the Company is no longer developing or commercializing any licensed product under the Regeneron Agreement. Either party may terminate the agreement upon the other party’s insolvency or bankruptcy or for material breach of the agreement by the other party that remains uncured for 90 days (or 30 days for payment‑related breaches). Regeneron has the right to terminate the agreement if the Company suspends its development or commercialization activities for a consecutive 12‑month period or does not grant a sublicense to a third‑party to perform such activities, or if the Company challenges any of the licensed patent rights. The Company may terminate the agreement at any time that is 18 months after the effective date of the agreement with 180 days’ written notice or with one years’ written notice if the Company terminates the agreement following U.S. marketing approval of a rilonacept product developed by the Company. The Company may also terminate the agreement with three month’s written notice if the products are determined to have certain safety concerns. The Company did not incur any research and development expense directly related to milestone payments due under the Regeneron Agreement during the year ended December 31, 2019 and 2018. MedImmune License Agreement In December 2017, the Company entered into a license agreement (the “MedImmune Agreement”) with MedImmune, Limited (“MedImmune”), pursuant to which MedImmune granted the Company an exclusive, sublicensable, worldwide license to certain intellectual property rights to make, use, develop and commercialize mavrilimumab. Under the MedImmune Agreement, the Company also acquired reference rights to relevant manufacturing and regulatory documents and MedImmune’s existing supply of mavrilimumab drug substance and product. The Company is obligated to use commercially reasonable efforts to develop and commercialize the licensed products. In exchange for these rights, the Company made an upfront payment of $8,000. The Company accounted for the acquisition of technology as an asset acquisition because it did not meet the definition of a business. The Company recorded the upfront payment as research and development expense in the consolidated statement of operations and comprehensive loss because the acquired technology represented in‑process research and development and had no alternative future use. In addition, the Company is obligated to make clinical, regulatory and initial sales milestone payments of up to $72,500 in aggregate for the first two indications, including, a $5,000 pass‑through payment due upon the achievement of a specified clinical milestone event which was met in the fourth quarter of 2018. Also included is a milestone payment of $10,000 due upon the earlier to occur of a specified regulatory milestone and December 31, 2018, unless the MedImmune Agreement is earlier terminated by either party. As of December 31, 2018 and 2017, the Company determined that the payment related to this milestone was probable and, therefore, recognized research and development expense and an accrued milestone of $10,000 during the year ended December 31, 2017. During the year ended December 31, 2019, the Company made both the $5,000 and $10,000 previously accrued milestone payments in accordance with the MedImmune Agreement. In addition, the Company is obligated to make clinical and regulatory milestone payments of up to $15,000 in the aggregate for each subsequent indication. The Company is obligated to make milestone payments to MedImmune of up to $85,000 upon the achievement of annual net sales thresholds up to, but excluding, $1,000,000 in annual net sales as well as additional milestone payments aggregating up to $1,100,000 upon the achievement of additional specified annual net sales thresholds starting at $1,000,000 and higher. The Company has also agreed to pay tiered royalties on escalating tiers of annual net sales of licensed products starting in the low double‑digit percentages and ending at twenty percent. Royalty rates are subject to reductions upon certain events. The Company is solely responsible for all development, manufacturing, and commercial activities and costs of the licensed products, including clinical studies or other tests necessary to support the use of a licensed product. The Company is also responsible for costs related to the filing, prosecution and maintenance of the licensed patent rights. The MedImmune Agreement will expire upon the expiration of the royalty term in the last country for the last indication, as defined in the agreement. Either party may terminate the agreement upon the other party’s insolvency or bankruptcy or for material breach of the agreement by the other party that remains uncured for 90 days. MedImmune has the right to terminate the agreement if the Company challenges any of the licensed patent rights. The Company may terminate the agreement at any time upon 90 days’ prior written notice. During the year ended December 31, 2019, the Company did not record research and development expense in connection with the milestone payments due under the MedImmune Agreement. During the year ended December 31, 2018, the Company recorded research and development expense $5,000, related primarily to a pass-through payment due upon the achievement of specified clinical milestone events due under the MedImmune Agreement. Kite Clinical Collaboration Agreement In December 2019, we entered into a clinical collaboration (the “Kite Agreement”) with Kite Pharma, Inc., a Gilead Company (“Kite”), to initiate a Phase 2 clinical trial evaluating the combination of Yescarta (axicabtagene ciloleucel) and mavrilimumab in relapsed or refractory large B-Cell lymphoma. The objective of the Phase 2 trial is to determine the effect of mavrilimumab on the safety of Yescarta. Treatment related induction of GM-CSF has been identified through clinical, translational and preclinical studies as a potential key signal associated with side effects of chimeric antigen receptor T, or CAR T, cell therapy. Preclinical evidence suggest the potential for interruption of GM-CSF signaling to disrupt CAR T cell mediated inflammation without disrupting anti-tumor activity. Kite will be the sponsor of this study and responsible for its conduct. Under the Kite Agreement, Kite and the Company shall share a portion of the costs incurred in conducting the study. The Kite Agreement will expire on the one-year anniversary of the date that Kite provides the clinical study report to the Company or unless otherwise terminated in accordance with the Kite Agreement. The Company evaluated the agreement and determined all costs and expenses will be recognized as incurred as research and development expenses. During the year ended December 31, 2019, the Company did not record any research and development expense in connection with the Kite Agreement.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Taxes
Income Taxes	11. Income Taxes As a company incorporated in Bermuda, the Company is principally subject to taxation in Bermuda. Under the current laws of Bermuda, tax on a company’s income is assessed at a zero percent tax rate. As a result, the Company has not recorded any income tax benefits from its losses incurred in Bermuda during each reporting period, and no net operating loss carryforwards will be available to the Company for those losses. In August 2015, the Company entered into agreements with its wholly owned subsidiary, Kiniksa US, under which Kiniksa US provides management and research and development services to the Company for which the Company pays costs plus a service fee. On March 9, 2019, the Company entered into an agreement with Primatope to license certain intellectual property rights related to KPL-404. Kiniksa US and Primatope are subject to tax in the United States for federal and state tax purposes. The Company has a wholly owned subsidiary in Europe, Kiniksa UK (formed in December 2018). Kiniksa UK has two wholly owned subsidiaries in Europe, Kiniksa Germany (formed in February 2019), and Kiniksa France (formed in June 2019). Each are subject to taxation in their respective countries. Income (loss) before benefit for income taxes consisted of the following: Years Ended December 31, 2019 2018 Bermuda $ (168,053) $ (105,562) Foreign (U.S., U.K., Germany, France) 4,139 2,121 $ (163,914) $ (103,441) The components of the Company’s income tax benefit for the years ended December 31, 2019 and 2018 are as follows: Years Ended December 31, 2019 2018 Current income tax (provision): Bermuda $ — $ — U.S. federal (567) (547) U.S. state (530) (217) Foreign (12) — Total current income tax (provision) (1,109) (764) Deferred income tax benefit: Bermuda — — U.S. federal 2,397 542 U.S. state 759 436 Foreign — — Total deferred income tax benefit 3,156 978 Total benefit (provision) for income taxes $ 2,047 $ 214 A reconciliation of the Bermuda statutory income tax rate of 0% to the Company’s effective income tax rate is as follows: Years Ended December 31, 2019 2018 Bermuda statutory income tax rate — % — % Foreign (U.S.) tax rate differential (0.5) (1.0) Research and development tax credits 2.2 1.5 Share-based compensation (0.5) 0.1 Permanent differences (0.1) — Change in valuation allowance (0.1) — U.S. state taxes, net of federal (0.3) (0.4) FDII 0.9 — Uncertain tax positions (0.3) — Effective income tax rate 1.3 % 0.2 % Net deferred tax assets consisted of the following: December 31, 2019 2018 Research and development tax credit carryforwards $ 238 $ 75 Depreciation and amortization (745) (639) Share-based compensation 3,746 1,000 Accrued expenses and other 1,273 829 Net operating losses 190 — Total deferred tax assets 4,702 1,265 Valuation allowance (330) (49) Net deferred tax assets $ 4,372 $ 1,216 As of December 31, 2019 and 2018, the Company had federal research and development tax credit carryforwards of approximately $228 and $0 respectively, available to reduce future tax liabilities, which begin to expire in 2039. As of December 31, 2019 and 2018, the Company had state research and development tax credit carryforwards of approximately $265 and $95 respectively, available to reduce future tax liabilities, which begin to expire in 2034. As required by ASC 740, the Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets. In order to utilize state research and development tax credits, the Company will need taxable income in the jurisdiction of where the credit was generated. The Company currently has no taxable income in certain state jurisdictions and thus management has determined that it is more likely than not that the Company will not recognize the benefits of state research and development tax credits generated in those jurisdictions, and as a result, a valuation allowance of $330 and $49 has been established at December 31, 2019 and 2018, respectively. Utilization of the state research and development tax credits may be subject to substantial annual limitation under Section 382 of the Internal Revenue Code of 1986 due to ownership changes that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain shareholders or public groups in the shares of a corporation by more than 50% over a three‑year period. Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2019 and 2018 were due primarily to an increase in state research and development tax credits and net operating losses from Primatope which are more likely than not to expire unutilized and were as follows: Years Ended December 31, 2019 2018 Valuation allowance at beginning of year $ (49) $ (27) Increases recorded to through the balance sheet (200) — Increases recorded to income tax provision (81) (22) Valuation allowance at end of year $ (330) $ (49) The valuation allowance increased by $281 in 2019 primarily as a result of additional California Research and Development (“R&D”) credits and the net operating loss carryovers at Primatope which may not be realized. The remaining deferred tax assets will be fully utilized in the United States based on future income generated under the cost‑plus arrangement in place. The Company recognizes the tax benefit from an uncertain tax position only if it is more-likely-than-not that the tax position will be sustained on examination by taxing authorities, based on the technical merits of the position. The tax benefits recognized in the financial statements from such a position are measured based on the largest benefit that has a greater than 50% likelihood of being realized upon ultimate settlement. The amount of unrecognized tax benefits is $528 and $0 as of December 31, 2019 and 2018, respectively. The net increase relates to new tax positions on Research and Development credits as a result of the R&D study performed in 2019. A roll forward of the Company’s uncertainties in its income tax provision liability is presented below: Years Ended December 31, 2019 2018 Gross balance at the beginning of year $ — $ — Gross increases based on current period tax positions 528 — Unrecognized tax benefits at the end of the year $ 528 $ — The Company’s policy is to record interest and penalties related to income taxes as part of its income tax provision. The Company had recorded immaterial interest on the tax positions during the year ended December 31, 2019 and no interest or penalties for the year ended December 31, 2018. The Company files income tax returns in the United States and certain state jurisdictions. Kiniksa US’s federal and state income tax returns are subject to tax examinations for the tax years ended December 31, 2016 and subsequent years. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service and state tax authorities to the extent utilized in a future period. There are currently no income tax examinations pending.

Net Loss per Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2019
Net Loss per Share
Net Loss per Share	12. Net Loss per Share The rights, including the liquidation and dividend rights, of the holders of Class A, Class B, Class A1 and Class B1 common shares are identical, except with respect to voting, transferability and conversion (see Note 8). As the liquidation and dividend rights are identical, losses are allocated on a proportionate basis and the resulting net loss per share attributed to common shareholders will, therefore, be the same for both Class A and Class B common shares on an individual or combined basis. Basic and diluted net loss per share attributable to common shareholders was calculated as follows: Years Ended December 31, 2019 2018 Numerator: Net loss attributable to common shareholders $ (161,867) $ (103,227) Denominator: Weighted average common shares outstanding—basic and diluted 54,049,477 29,547,427 Net loss per share attributable to common shareholders— basic and diluted $ (2.99) $ (3.49) The Company’s unvested restricted shares and restricted share units have been excluded from the computation of basic net loss per share attributable to common shareholders. The Company’s potentially dilutive securities, which include options, unvested restricted shares and unvested RSUs, have been excluded from the computation of diluted net loss per share attributable to common shareholders as the effect would be to reduce the net loss per share attributable to common shareholders. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common shareholders is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common shareholders for the periods indicated because including them would have had an anti-dilutive effect: As of December 31, 2019 2018 Options to purchase common shares 8,491,734 5,960,939 Unvested restricted shares — 877,219 Unvested restricted share units 328,296 — 8,820,030 6,838,158

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies
Commitments and Contingencies	13. Commitments and Contingencies License Agreements The Company has entered into license agreements with various parties under which it is obligated to make contingent and non‑contingent payments (see Note 10). Manufacturing Commitments The Company entered into agreements with several contract manufacturing organizations to provide preclinical and clinical trial materials. As of December 31, 2019, the Company had committed to minimum payments under these agreements totaling $2,863 which are due during the year ending December 31, 2020. Rilonacept Long-Term Incentive Plan During the year ended December 31, 2019, the Company granted a cash award and the First RSU Award to employees under the RLTIP. The cash award vests upon the achievement of the RLTIP Milestone, subject to the recipient’s continued employment. The First RSU Award becomes eligible to vest upon the achievement of the RLTIP Milestone, and will vest upon the first anniversary of such date, subject to the recipient’s continued employment through that date. As of December 31, 2019, the Company estimates cash payments of $2,083 under the RLTIP. In the event the RLTIP Milestone is not achieved, the cash award will not be paid and the First RSU Award will not vest. Indemnification Agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors, officers and other key personnel that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors, officers or other key personnel. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company does not believe that the outcome of any claims under indemnification arrangements will have a material effect on its financial position, results of operations or cash flows, and it has not accrued any liabilities related to such obligations in its consolidated financial statements as of December 31, 2019 or 2018. Legal Proceedings The Company is not a party to any litigation and does not have contingency reserves established for any litigation liabilities.

Benefit Plans

Benefit Plans	12 Months Ended
	Dec. 31, 2019
Benefit Plans
Benefit Plans	14. Benefit Plans The Company has established a defined-contribution savings plan under Section 401(k) of the Internal Revenue Code. This plan covers substantially all employees who meet minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. The Company provides matching contributions of 100% of the first 3% of each participant’s salary contributed, plus 50% for each of the next 2% contributed. Employees are immediately and fully vested in their own contributions and the Company’s match. During the years ended December 31, 2019 and 2018, the Company contributed $851 and $315, respectively, to the plan.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Summary of Significant Accounting Policies
Principles of Consolidation	Principles of Consolidation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company and its wholly owned subsidiaries, Kiniksa Pharmaceuticals Corp. (“Kiniksa US”), Primatope Therapeutics, Inc. (“Primatope”) and Kiniksa Pharmaceuticals (UK), Ltd. (“Kiniksa UK”) as well as the subsidiaries of Kiniksa UK, Kiniksa Pharmaceuticals (Germany) GmbH (“Kiniksa Germany”) and Kiniksa Pharmaceuticals (France) SARL (“Kiniksa France”), after elimination of all significant intercompany accounts and transactions. In assessing the consolidation requirement for variable interest entities (“VIE”s), the Company focuses on identifying whether it has both the power to direct the activities that most significantly impact the VIE’s economic performance and the obligation to absorb losses or the right to receive benefits from the VIE. In the event that the Company is the primary beneficiary of a VIE, the assets, liabilities, and results of operations of the VIE would be included in the Company’s consolidated financial statements. At December 31, 2019 and 2018 and during the years then ended, the Company was not the primary beneficiary of a VIE.
Use of Estimates	Use of Estimates The preparation of the Company’s consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the accrual for research and development expenses and the valuation of common shares and share‑based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates.
Reporting and Functional Currency	Reporting and Functional Currency The financial results of the Company's global activities are reported in U.S. dollars (“USD”) and its foreign subsidiaries generally utilize their respective local currency to be their functional currency. Transactions in other currencies are recorded in the functional currency at the rate of exchange prevailing when the transactions occur. Monetary assets and liabilities denominated in other currencies are re-measured into the functional currency at the rate of exchange in effect at the balance sheet date. Exchange gains and losses arising from re-measurement of foreign currency-denominated monetary assets and liabilities are included in income in the period in which they occur. For our foreign subsidiaries where the local currency is the functional currency, assets and liabilities denominated in local currencies are translated into USD at end-of-period exchange rates and the resulting translation adjustments are reported as a component of accumulated other comprehensive income (loss) within shareholders' equity (deficit).
Cash and Cash Equivalents	Cash and Cash Equivalents The Company classifies deposits in banks, money market funds and cash invested temporarily in various instruments with maturities of three months or less at the time of purchase as cash and cash equivalents. At December 31, 2019 and 2018, cash and cash equivalents consisted principally of U.S. Treasury notes, amounts held in money market accounts and cash on deposit at commercial banks.
Short-term Investments	Short‑Term Investments The Company generally invests its excess cash in money market funds and short‑term investments in U.S. Treasury notes. Such investments included in short‑term investments on the Company’s consolidated balance sheets are considered available‑for‑sale debt securities and are reported at fair value with unrealized gains and losses included as a component of shareholders’ equity (deficit). Realized gains and losses, if any, on short‑term investments are included in interest income. The Company evaluates its short‑term investments with unrealized losses for other‑than‑temporary impairment. When assessing short‑term investments for other‑than‑temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary,” the Company reduces the investment to fair value through a charge to the consolidated statement of operations and comprehensive loss. No such adjustments were necessary during the periods presented.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk consist principally of cash, cash equivalents and short-term investments. At December 31, 2019 and 2018, substantially all of the Company’s cash, cash equivalents and short-term investments were held at two financial institutions. The Company generally maintains balances in various operating accounts at financial institutions that management believes to be of high credit quality, in amounts that may exceed federally insured limits. The Company has not experienced any losses related to its cash, cash equivalents and short-term investments and does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships.
Restricted Cash	Restricted Cash In conjunction with the Company’s lease agreement entered into in March 2018 (see Note 5), the Company maintains a letter of credit for the benefit of the landlord. As of December 31, 2019 and 2018, the underlying cash balance of $210 securing this letter of credit, was classified as non‑current in its consolidated balance sheet.
Property and Equipment	Property and Equipment Property and equipment are recorded at cost and depreciated over the estimated useful lives of the related assets using the straight-line method. Maintenance and repairs are charged to expense as incurred. When assets are retired or otherwise disposed of, the cost of these assets and related accumulated depreciation or amortization are eliminated from the consolidated balance sheet and any resulting gains or losses are included in the consolidated statement of operations and comprehensive loss in the period of disposal. The expected useful lives of the respective assets are as follows: Estimated Useful Life Computer hardware and software 3 - 5 years Laboratory equipment 5 years Furniture, fixtures and vehicles 5 - 7 years Leasehold improvements Shorter of estimated useful life or lease term
Impairment of Long‑Lived Assets	Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. To date, the Company has not recorded any impairment losses on long-lived assets.
Deferred Offering Costs	Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process common equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded as a reduction to the carrying value of convertible preferred shares or in shareholders’ equity (deficit) as a reduction of additional paid-in capital generated as a result of the offering. Should an in-process equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the consolidated statements of operations and comprehensive loss. As of December 31, 2018, the Company recorded deferred offering costs of $433 related to the follow-on offering of its Class A common shares and private placement of its Class A1 Common Shares. The follow-on offering and concurrent private placement were finalized in February 2019, and all prior deferred costs were recorded as a reduction to the carrying value. There were no deferred offering costs recorded as of December 31, 2019.
Fair Value Measurements	Fair Value Measurements Certain assets and liabilities of the Company are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: · Level 1—Quoted prices in active markets for identical assets or liabilities. · Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. · Level 3—Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s restricted cash, which is held in a money market fund, is carried at fair value, determined based on Level 1 inputs in the fair value hierarchy described above (see Note 3). The Company’s cash equivalents and short-term investments, consisting of money market accounts and U.S. Treasury notes, are carried at fair value, determined based on Level 1 and 2 inputs in the fair value hierarchy described above (see Note 3). The carrying values of the Company’s prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values due to the short-term nature of these assets and liabilities.
Leases	Leases In February 2016, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), which set forth the principles for recognition, measurement, presentation and disclosure of lease arrangements to enhance the transparency and comparability of financial reporting related to the arrangements. ASU 2016-02, including subsequently issued amendments, is collectively referred to as Accounting Standards Codification, Leases (Topic 842) (“ASC 842”). The Company adopted the new standard on January 1, 2019 using the modified retrospective transition approach as applied to leases existing as of the adoption date. The standard will be applied to all leases entered into after the initial adoption date. At the inception of an arrangement, the Company determines whether the arrangement is or contains a “lease” as defined by ASC 842. A lease is an arrangement, or part of an arrangement, that conveys the right to control the use of identified property, plant, or equipment (an identified asset) for a period of time in exchange for consideration. The Company determines if the arrangement conveys the right to control the use of an identified asset for a period of time. It assesses throughout the period of use whether the Company has both of the following (1) the right to obtain substantially all of the economic benefits from use of the identified asset and (2) the right to direct the use of the identified asset. This determination is reassessed if the terms of the arrangement are changed. Leases are classified as operating or finance leases based on the terms of the lease agreement and certain characteristics of the identified asset. Right-of-use (“ROU”) assets and lease liabilities are recognized at lease commencement date based on the present value of the minimum future lease payments. Most leases with a term greater than one year are recognized on the balance sheet as ROU assets with corresponding lease liabilities and, if applicable, long-term lease liabilities. The Company has elected not to recognize leases with a term of one year or less on its balance sheet. Operating leases, ROU assets and their corresponding lease liabilities are recorded based on the present value of lease payments over the expected remaining lease term. However, certain adjustments to the ROU assets may be required for items such as incentives received. The interest rate implicit in lease arrangements is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. In accordance with the guidance in ASU 2016-02, components of a lease should be split into three categories: lease components (e.g., land, building, etc.), non-lease components (e.g., common area maintenance, consumables, etc.), and non-components (e.g., property taxes, insurance, etc.); then the fixed and in-substance fixed contract consideration (including any related to non-components) must be allocated based on fair values to the lease components and non-lease components. Although separation of lease and non-lease components is required, certain practical expedients are available. Companies may elect the practical expedient to not separate lease and non-lease components. In which case, the Company would account for each lease component and the related non-lease component together as a single component. The Company has elected to account for the lease and non-lease components of each of its operating leases as a single lease component and allocate all of the arrangement consideration to the lease component only. The lease component results in an operating right-of-use asset being recorded on the balance sheet and amortized on a straight-line basis as lease expense.
Segment Information	Segment Information The Company manages its operations as a single operating segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is on developing and delivering therapeutic medicines for patients suffering from debilitating diseases with significant unmet medical need.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred to discover, research and develop drug candidates, including personnel expenses, share‑based compensation expense, allocated facility‑related and depreciation expenses, third‑party license fees and external costs of outside vendors engaged to conduct preclinical and clinical development activities and clinical trials as well as to manufacture clinical trial materials. Non‑refundable prepayments for goods or services that will be used or rendered for future research and development activities are recorded as prepaid expenses. Such amounts are recognized as an expense as the goods are delivered or the related services are performed, or until it is no longer expected that the goods will be delivered, or the services rendered. Milestone and other payments made to third-parties with respect to in-process research and development, in accordance with the Company’s license, acquisition and other similar agreements are expensed when determined to be probable and estimable.
Research Contract Costs and Accruals	Research Contract Costs and Accruals The Company has entered into various research and development-related contracts with companies both inside and outside of the United States. The related costs are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research and development costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies or clinical trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ materially from the Company's estimates. The Company's historical accrual estimates have not been materially different from the actual costs.
Patent Costs	Patent Costs The Company charges patent-related costs in connection with filing and prosecuting patent applications to operations as incurred as their realization is uncertain. These costs are classified as general and administrative expenses.
Share-Based Compensation	Share‑Based Compensation The Company measures all share-based awards granted to employees and directors based on their fair value on the date of the grant and recognizes compensation expense for those awards over the requisite service period. Forfeitures are accounted for as they occur. The Company issues share-based awards with both service-based vesting conditions and performance-based vesting conditions. Expense for awards with service-based vesting is recorded using the straight-line method, and expense for awards with performance-based vesting conditions is recognized using the accelerated-attribution method. For share-based awards granted to consultants and non-employees, compensation expense is recognized over the vesting period of the awards, which is generally the period during which services are rendered by such consultants and non-employees until completed. At the end of each financial reporting period prior to completion of the service, the fair value of these awards is remeasured using the then-current fair value of the Company's Class A common shares and updated assumption inputs in the Black-Scholes option-pricing model. The Company classifies share-based compensation expense in its consolidated statements of operations and comprehensive loss in the same manner in which the award recipient's payroll costs are classified or in which the award recipient's service payments are classified. The fair value of each restricted share award is estimated on the date of grant based on the fair value of the Company’s Class A common shares or Class B common shares on that same date. The fair value of each option grant is estimated on the date of grant using the Black-Scholes option-pricing model, which requires inputs based on certain subjective assumptions, including the expected share price volatility, the expected term of the award, the risk-free interest rate, and expected dividends (see Note 9). Prior to May 2018, the Company was a private company and, accordingly, lacks company-specific historical and implied volatility information for its shares. Therefore, it estimates its expected share price volatility based on the historical volatility of publicly traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded share price. The expected term of the Company’s options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The expected term of options granted to non-employees is equal to the contractual term of the option award. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends on common shares and does not expect to pay any cash dividends in the foreseeable future. The fair value of each restricted share unit award is based on the closing price of the Company’s Class A common shares on the date of grant. Restricted share unit awards with an associated performance condition are evaluated on a regular basis for probability of achievement, to determine the timing of recording share-based compensation expense in the Company’s consolidated statements of operations and comprehensive loss.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss as well as other changes in shareholders’ equity (deficit) that result from transactions and economic events other than those with shareholders. For the year ended December 31, 2019 and 2018, the Company’s other comprehensive loss was comprised of unrealized gain (loss) on short-term investments and currency translation adjustments, net of tax.
Income Taxes	Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the benefit for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. As an exempted company incorporated under the laws of Bermuda, the Company is principally subject to taxation in Bermuda. Under the current laws of Bermuda, tax on a company’s income is assessed at a zero percent tax rate. As a result, the Company has not recorded any income tax benefits from losses incurred in Bermuda during each reporting period, and no net operating loss carryforwards will be available to the Company for those losses. The Company’s wholly owned U.S. subsidiary, Kiniksa US, and Primatope are subject to federal and state income taxes in the United States. The Company’s wholly owned subsidiary Kiniksa UK., and its wholly owned subsidiaries, Kiniksa Germany and Kiniksa France are subject to taxation in their respective countries. The Company’s benefit for income taxes primarily relates to net credits earned against taxable income generated by its wholly owned subsidiaries, primarily, Kiniksa US, under cost‑plus arrangements that they have with the Company. The benefit for income taxes is impacted by the Foreign Derived Intangible Income, or (“FDII”), deduction and U.S. federal and state research and development tax credits. FDII was enacted as part of the tax reform enacted by the United States in December 2017, generally referred to as the U.S. Tax Cuts and Jobs Act with additional proposed regulations and guidance issued in 2019. Upon the completion of the Company’s assessment, the Company has included the tax impact of FDII in its income tax expense for the year ended December 31, 2019, based on its understanding of the rules available at the time of this filing. However, the amounts recorded could be impacted in the future when the proposed regulations and guidance are finalized. The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties. In 2019, the Company identified an uncertain tax position related to historic research and development credits as a result of a R&D study performed (see Note 11).
Net Loss per Share	Net Loss per Share The Company follows the two‑class method when computing net loss per share as the Company has issued shares that meet the definition of participating securities. The two‑class method determines net loss per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two‑class method requires income available to common shareholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. Basic net loss per share attributable to common shareholders is computed by dividing the net loss attributable to common shareholders by the weighted average number of common shares outstanding for the period. Diluted net loss attributable to common shareholders is computed by adjusting net loss attributable to common shareholders to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net loss per share attributable to common shareholders is computed by dividing the diluted net loss attributable to common shareholders by the weighted average number of common shares outstanding for the period, including potential dilutive common shares. For purpose of this calculation, outstanding options, unvested restricted common shares and convertible preferred shares are considered potential dilutive common shares.
Recently Adopted and Recently Issued Accounting Pronouncements	Recently Adopted Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued Account Standards Update (“ASU”), No. 2016-02, Leases (Topic 842) (“ASU 2016-02”) . The standard, including subsequently issued amendments, collectively referred to as Accounting Standards Codification (“ASC”) 842, established principles of recognition, measurement, presentation and disclosure of lease arrangements applicable to lessees and lessors in order to enhance the transparency and compatibility of financial reporting related to the arrangements, including with respect to the amount, timing and uncertainty of cash flows arising from a lease. The Company adopted new accounting guidance regarding the accounting for leases as of January 1, 2019 using a modified retrospective transition approach that was applied to leases existing as of, or entered into prior to, January 1, 2019. See Note 2, Summary of Significant Accounting Policies, “Leases” for a discussion of the Company’s policy with respect to this standard and Note 5, “Leases” for a discussion of the Company’s adoption of this standard and its impact on its consolidated financial statements and related disclosures. Upon the adoption of ASC 842, the Company recorded operating lease right-of-use assets of $3,682 and operating lease liabilities of $3,917 for its leases which were in effect and had commenced prior to January 1, 2019 and had original lease terms of more than 12 months. Recently Issued Accounting Pronouncements In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other— Internal-Use Software (Subtopic 350-40) (“ASU 2018-15”) , which amends ASC 350-40 to address a customer’s accounting for implementation costs incurred in a cloud computing arrangement (“CCA”) that is a service contract. ASU 2018-15 aligns the accounting for costs incurred to implement a CCA that is a service contract with the guidance on capitalizing costs associated with developing or obtaining internal-use software. Specifically, the ASU amends ASC 350 to include in its scope implementation costs of a CCA that is a service contract and clarifies that a customer should apply ASC 350-40 to determine which implementation costs should be capitalized in a CCA that is considered a service contract. The standard became effective for the Company beginning on January 1, 2020. The Company is currently evaluating the potential impact that ASC 350-40 may have on its consolidated financial statements and related disclosures . In June 2016, the FASB, issued ASU 2016-13, Financial Instruments: Credit Losses (Topic 326)(“ASU 2016-13)” , as clarified in ASU 2019-04 and ASU 2019-05. The objective of the standard is to provide information about expected credit losses on financial instruments at each reporting date and to change how other-than-temporary impairments on investment securities are recorded. The standard became effective for the Company beginning on January 1, 2020. The Company does not anticipate the adoption of this ASU to have a material impact on its consolidated financial statements and related disclosures. In December 2019, the FASB issued ASU 2019-12, Simplifying the Accounting for Income Taxes (Topic 740)(“ASU 2019-12”) . The objective of the standard is to improve areas of GAAP by removing certain exceptions permitted by ASC Topic 740 Income Taxes and clarifying existing guidance to facilitate consistent application. The standard will become effective for the Company beginning on January 1, 2021. The Company is currently evaluating the new standard to determine the potential impact of ASU 2019-12 on its consolidated financial statements and related disclosures.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2019
Summary of Significant Accounting Policies
Schedule of expected useful lives of assets	Estimated Useful Life Computer hardware and software 3 - 5 years Laboratory equipment 5 years Furniture, fixtures and vehicles 5 - 7 years Leasehold improvements Shorter of estimated useful life or lease term

Fair Value of Financial Asset_2

Fair Value of Financial Assets and Liabilities (Tables)	12 Months Ended
	Dec. 31, 2019
Fair Value of Financial Assets and Liabilities
Schedule of financial assets and liabilities measured at fair value on a recurring basis	Fair Value Measurements as of December 31, 2019 Using: Level 1 Level 2 Level 3 Total Assets: Restricted cash — money market funds $ 210 $ — $ — $ 210 Cash equivalents — money market funds 25,207 — — 25,207 Cash equivalents — U.S. Treasury notes — 10,192 — 10,192 Short-term investments — U.S. Treasury notes — 186,452 — 186,452 $ 25,417 $ 196,644 $ — $ 222,061 Fair Value Measurements as of December 31, 2018 Using: Level 1 Level 2 Level 3 Total Assets: Restricted cash — money market funds $ 210 $ — $ — $ 210 Cash equivalents — money market funds 29,721 — — 29,721 Cash equivalents — U.S. Treasury notes — 15,634 — 15,634 Short-term investments — U.S. Treasury notes — 235,328 — 235,328 $ 29,931 $ 250,962 $ — $ 280,893

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2019
Property and Equipment, Net
Schedule of property and equipment, net	December 31, December 31, 2019 2018 Furniture, fixtures and vehicles $ 47 $ 91 Computer hardware and software 344 249 Leasehold improvements 3,627 2,676 Lab equipment 4,685 3,107 Construction in progress 20 552 Total property and equipment 8,723 6,675 Less: Accumulated depreciation (2,325) (319) Total property and equipment, net $ 6,398 $ 6,356

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2019
Leases
Schedule of maturities of operating lease liabilities	As of December 31, 2020 $ 1,821 2021 972 2022 — 2023 and thereafter — Total future minimum lease payments $ 2,793 Less imputed interest (141) Present value of lease liabilities $ 2,652 As of December 31, 2019 $ 1,394 2020 1,821 2021 972 2022 and thereafter — Total future minimum lease payments $ 4,187

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2019
Accrued Expenses
Schedule of accrued expenses	December 31, December 31, 2019 2018 Accrued research and development expenses $ 11,813 $ 9,656 Accrued employee compensation and benefits 7,089 5,678 Accrued legal and professional fees 1,087 994 Other 426 90 $ 20,415 $ 16,418

Share Based Compensation (Table

Share Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of stock option activity under the Plans	Weighted Weighted Average Average Remaining Aggregate Number of Exercise Contractual Intrinsic Shares Price Term Value (in years) Outstanding as of December 31, 2018 5,960,939 $ 10.25 8.56 $ 108,352 Granted 3,608,588 $ 13.44 Exercised (150,253) $ 3.93 Forfeited (927,540) $ 15.26 Outstanding as of December 31, 2019 8,491,734 $ 11.17 7.88 $ 27,217 Options exercisable as of December 31, 2019 3,373,659 $ 7.29 6.24 $ 19,903 Options unvested as of December 31, 2019 5,118,075 $ 13.74 8.96 $ 7,314
Schedule of share-based compensation expense was classified in the consolidated statements of operations and comprehensive loss	Years Ended December 31, 2019 2018 Research and development expenses $ 5,746 $ 2,285 General and administrative expenses 9,334 3,416 $ 15,080 $ 5,701
Employees and Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of stock option valuation assumptions presented on weighted average basis	Years Ended December 31, 2019 2018 Risk-free interest rate 2.07 % 2.82 % Expected term (in years) 6.22 6.40 Expected volatility 79.14 % 75.04 % Expected dividend yield % %
Non-employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of stock option valuation assumptions presented on weighted average basis	Years Ended December 31, 2019 2018 Risk-free interest rate 1.38 % 2.91 % Expected term (in years) 2.77 7.35 Expected volatility 68.17 % 74.18 % Expected dividend yield % %
Restricted shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of restricted share activity	Class A Class B Weighted Weighted Average Average Number of Grant Date Number of Grant Date Shares Fair Value Shares Fair Value Unvested restricted shares outstanding as of December 31, 2018 133,812 $ 0.000273235 743,407 $ 0.000273235 Granted — — — — Vested (133,812) $ 0.000273235 (743,407) $ 0.000273235 Unvested restricted shares outstanding as of December 31, 2019 — — — —
Restricted Share Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of restricted share activity	Weighted Average Number of Grant Date Shares Fair Value Unvested RSUs as of December 31, 2018 — $ — Granted 328,296 $ 12.93 Vested — $ — Forfeited — $ — Unvested RSUs as of December 31, 2019 328,296 $ 12.93

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Income Taxes
Schedule of income (loss) before benefit for income taxes	Years Ended December 31, 2019 2018 Bermuda $ (168,053) $ (105,562) Foreign (U.S., U.K., Germany, France) 4,139 2,121 $ (163,914) $ (103,441)
Schedule of components of income tax benefit	Years Ended December 31, 2019 2018 Current income tax (provision): Bermuda $ — $ — U.S. federal (567) (547) U.S. state (530) (217) Foreign (12) — Total current income tax (provision) (1,109) (764) Deferred income tax benefit: Bermuda — — U.S. federal 2,397 542 U.S. state 759 436 Foreign — — Total deferred income tax benefit 3,156 978 Total benefit (provision) for income taxes $ 2,047 $ 214
Schedule of reconciliation of the Bermuda statutory income tax rate of 0% to the Company’s effective income tax rate	Years Ended December 31, 2019 2018 Bermuda statutory income tax rate — % — % Foreign (U.S.) tax rate differential (0.5) (1.0) Research and development tax credits 2.2 1.5 Share-based compensation (0.5) 0.1 Permanent differences (0.1) — Change in valuation allowance (0.1) — U.S. state taxes, net of federal (0.3) (0.4) FDII 0.9 — Uncertain tax positions (0.3) — Effective income tax rate 1.3 % 0.2 %
Summary of net deferred tax assets	December 31, 2019 2018 Research and development tax credit carryforwards $ 238 $ 75 Depreciation and amortization (745) (639) Share-based compensation 3,746 1,000 Accrued expenses and other 1,273 829 Net operating losses 190 — Total deferred tax assets 4,702 1,265 Valuation allowance (330) (49) Net deferred tax assets $ 4,372 $ 1,216
Schedule of changes in the valuation allowance for deferred tax assets	Years Ended December 31, 2019 2018 Valuation allowance at beginning of year $ (49) $ (27) Increases recorded to through the balance sheet (200) — Increases recorded to income tax provision (81) (22) Valuation allowance at end of year $ (330) $ (49)
Schedule of uncertainties in income tax provision liability	Years Ended December 31, 2019 2018 Gross balance at the beginning of year $ — $ — Gross increases based on current period tax positions 528 — Unrecognized tax benefits at the end of the year $ 528 $ —

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2019
Net Loss per Share
Schedule of basic and diluted net loss per share attributable to common shareholders	Years Ended December 31, 2019 2018 Numerator: Net loss attributable to common shareholders $ (161,867) $ (103,227) Denominator: Weighted average common shares outstanding—basic and diluted 54,049,477 29,547,427 Net loss per share attributable to common shareholders— basic and diluted $ (2.99) $ (3.49)
Schedule of anti-dilutive securities excluded from the computation of diluted net loss per share attributable to common shareholders	As of December 31, 2019 2018 Options to purchase common shares 8,491,734 5,960,939 Unvested restricted shares — 877,219 Unvested restricted share units 328,296 — 8,820,030 6,838,158

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation (Details) $ / shares in Units, $ in Thousands	Mar. 01, 2019USD ($)$ / sharesshares	Feb. 04, 2019USD ($)$ / sharesshares	Jun. 22, 2018USD ($)$ / sharesshares	May 29, 2018USD ($)$ / sharesshares	May 11, 2018	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	May 31, 2018shares
Nature of the Business and Basis of Presentation
Reverse stock split					2.73235
Liquidity
Accumulated deficit						$ 356,092	$ 194,225
Net losses						161,867	103,227
Cash used in operations						158,369	81,012
Cash, cash equivalents and short-term investments						233,380
Class A common shares
Nature of the Business and Basis of Presentation
Number of shares issued on conversion of convertible preferred shares | shares				5,546,019				5,546,019
Class B common shares
Nature of the Business and Basis of Presentation
Number of shares issued on conversion of convertible preferred shares | shares				1,070,502				1,070,502
Class A1 common shares
Nature of the Business and Basis of Presentation
Number of shares issued on conversion of convertible preferred shares | shares				12,995,954				12,995,954
Class B1 common shares
Nature of the Business and Basis of Presentation
Number of shares issued on conversion of convertible preferred shares | shares				16,057,618				16,057,618
Initial Public Offering
Nature of the Business and Basis of Presentation
Aggregate proceeds from offerings net of underwriter discounts and commissions and other offering costs							155,536
Initial Public Offering | Class A common shares
Nature of the Business and Basis of Presentation
Issuance of stock (in shares) | shares				8,477,777
Share price (in dollars per share) | $ / shares				$ 18
Gross proceeds from IPO				$ 152,600
Gross proceeds from offering							$ 159,194
Over-allotment | Class A common shares
Nature of the Business and Basis of Presentation
Issuance of stock (in shares) | shares	161,126		1,006,425
Share price (in dollars per share) | $ / shares	$ 18.26		$ 18
Gross proceeds from IPO			$ 18,116
Gross proceeds from offering	$ 2,942
Follow-On Public Offering and Private Placement
Nature of the Business and Basis of Presentation
Aggregate proceeds from offerings net of underwriter discounts and commissions and other offering costs	$ 82,988					82,988
Follow-On Public Offering and Private Placement | Common Class A and Class A1 common shares
Nature of the Business and Basis of Presentation
Gross proceeds from offering		$ 85,000
Follow-On Offering | Class A common shares
Nature of the Business and Basis of Presentation
Issuance of stock (in shares) | shares		2,654,984
Share price (in dollars per share) | $ / shares		$ 18.26
Gross proceeds from offering						$ 48,595
Private Placement | Class A1 common shares
Nature of the Business and Basis of Presentation
Issuance of stock (in shares) | shares		2,000,000
Share price (in dollars per share) | $ / shares		$ 18.26

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Concentrations of Credit Risk and Restricted Cash (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)item	Dec. 31, 2018USD ($)item
Restricted cash
Cash securing letter of credit | $	$ 210	$ 210
Cash and cash equivalents | Credit concentration
Concentration risk
Number of financial institutions holding cash, cash equivalents and short-term investments | item	2	2

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2019
Laboratory equipment
Property and Equipment, Net
Expected useful life	5 years
Minimum | Computer hardware and software
Property and Equipment, Net
Expected useful life	3 years
Minimum | Furniture, fixtures, and vehicles
Property and Equipment, Net
Expected useful life	5 years
Maximum | Computer hardware and software
Property and Equipment, Net
Expected useful life	5 years
Maximum | Furniture, fixtures, and vehicles
Property and Equipment, Net
Expected useful life	7 years

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Deferred Offering Costs (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred offering costs
Deferred offering costs	$ 0	$ 433
Common Class A and Class A1 common shares | Follow-On Public Offering and Private Placement
Deferred offering costs
Deferred offering costs		$ 433

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Taxes
Bermuda statutory income tax rate	0.00%	0.00%
Income tax benefits - Bermuda	$ 0	$ 0
Net operating loss carryforwards - Bermuda	$ 0	$ 0

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Recently Adopted Accounting Pronouncements (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019
Operating lease assets and liabilities
Operating lease right-of-use assets	$ 1,927
Operating lease liabilities	$ 2,652
ASU 2016-02 | Cumulative Effect of Adoption
Operating lease assets and liabilities
Operating lease right-of-use assets		$ 3,682
Operating lease liabilities		$ 3,917

Fair Value of Financial Asset_3

Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets Transfers
Fair value of assets transferred from Level 1 to Level 2	$ 0	$ 0
Fair value of assets transferred from Level 2 to Level 1	0	0
Fair value of assets transferred from Level 1 to Level 3	0	0
Fair value of assets transferred from Level 2 to Level 3	0	0
Fair value of assets transferred from Level 3 to Level 1	0	0
Fair value of assets transferred from Level 3 to Level 2	0	0
U.S. Treasury Notes
Assets
Amortized cost of short-term investments	186,415	235,332
Unrealized gain (loss) on short-term investments	37	(4)
Short-term investments	186,452	235,328
Fair Value | Recurring basis
Assets
Assets	222,061	280,893
Fair Value | Recurring basis | Money Market Funds
Assets
Restricted cash	210	210
Cash equivalents	25,207	29,721
Fair Value | Recurring basis | U.S. Treasury Notes
Assets
Cash equivalents	10,192	15,634
Short-term investments	186,452	235,328
Fair Value | Recurring basis | Level 1
Assets
Assets	25,417	29,931
Fair Value | Recurring basis | Level 1 | Money Market Funds
Assets
Restricted cash	210	210
Cash equivalents	25,207	29,721
Fair Value | Recurring basis | Level 2
Assets
Assets	196,644	250,962
Fair Value | Recurring basis | Level 2 | U.S. Treasury Notes
Assets
Cash equivalents	10,192	15,634
Short-term investments	$ 186,452	$ 235,328

Property and Equipment, Net (De

Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Property and Equipment, Net
Total property and equipment	$ 8,723	$ 6,675
Less: Accumulated depreciation	(2,325)	(319)
Total property and equipment, net	6,398	6,356
Depreciation expense	2,068	286
Furniture, fixtures, and vehicles
Property and Equipment, Net
Total property and equipment	47	91
Computer hardware and software
Property and Equipment, Net
Total property and equipment	344	249
Leasehold improvements
Property and Equipment, Net
Total property and equipment	3,627	2,676
Lab Equipment
Property and Equipment, Net
Total property and equipment	4,685	3,107
Construction in progress
Property and Equipment, Net
Total property and equipment	$ 20	$ 552

Leases - Operating Leases (Deta

Leases - Operating Leases (Details) - Kiniksa US $ in Thousands	Dec. 21, 2018USD ($)ft²	Mar. 31, 2017USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2019	Nov. 07, 2018ft²	Jun. 26, 2018ft²	Mar. 31, 2016ft²
Maximum
Operating leases
Remaining lease terms				2 years
Wellesley Hills office
Operating leases
Area of leased space after expansion | ft²							10,800
Monthly lease payments, inclusive of base rent and ancillary charges | $		$ 27
Lexington office
Operating leases
Area of leased space after expansion | ft²					55,924	27,244
Monthly base rent payment | $			$ 138
San Diego office
Operating leases
Area of leased space after expansion | ft²	4,400
Monthly base rent payment | $	$ 13

Leases - Lease Cost and Maturit

Leases - Lease Cost and Maturities of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Lease cost
Operating lease cost	$ 1,443
Variable lease cost	$ 152
Weighted average lease term	1 year 5 months 19 days
Discount rate	7.16%
Maturities of operating lease liabilities
2020	$ 1,821
2021	972
Total future minimum lease payments	2,793
Less imputed interest	(141)
Present value of lease liabilities	$ 2,652
Future minimum lease payments
2019		$ 1,394
2020		1,821
2021		972
Total future minimum lease payments		$ 4,187

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accrued Expenses
Accrued research and development expenses	$ 11,813	$ 9,656
Accrued employee compensation and benefits	7,089	5,678
Accrued legal and professional fees	1,087	994
Other	426	90
Accrued expenses	$ 20,415	$ 16,418

Convertible Preferred Shares (D

Convertible Preferred Shares (Details) $ / shares in Units, $ in Thousands	1 Months Ended					12 Months Ended
	May 31, 2018$ / sharesshares	Feb. 28, 2018USD ($)$ / sharesshares	Mar. 31, 2017USD ($)$ / sharesshares	Sep. 30, 2016USD ($)$ / sharesshares	Oct. 31, 2015USD ($)$ / sharesshares	Dec. 31, 2019USD ($)director$ / sharesshares	Dec. 31, 2018USD ($)directorVote	May 29, 2018shares	Dec. 31, 2017$ / sharesshares
Convertible Preferred Shares
Preferred shares designated						0
Preferred stock, shares issued (in shares)						0
Payment of offering expenses | $						$ 118	$ 3,657
Preferred stock, cash dividends declared or paid | $							$ 0
Convertible Preferred Shares (Series A, B and C)
Convertible Preferred Shares
Preferred shares designated		35,670,093				0			22,885,492
Preferred stock, shares issued (in shares)						0
Convertible preferred shares, par value (in dollars per share) | $ / shares		$ 0.000273235							$ 0.000273235
Number of directors entitled to elect | director							2
Series A convertible preferred shares
Convertible Preferred Shares
Preferred shares designated									17,128,120
Preferred stock, shares issued (in shares)				9,099,311	8,028,809
Share price per share | $ / shares				$ 4.6707	$ 4.6707
Proceeds from issuance of shares | $				$ 42,499	$ 37,398
Payment of offering expenses | $				$ 1	$ 102
Number of votes for each Class B common share | Vote							10
Original issue price (per share) | $ / shares	$ 4.6707
Convertible ratio to Class B common share	1
Series B convertible preferred shares
Convertible Preferred Shares
Preferred shares designated									5,757,372
Preferred stock, shares issued (in shares)			5,757,372
Share price per share | $ / shares			$ 6.9475
Proceeds from issuance of shares | $			$ 39,873
Payment of offering expenses | $			$ 127
Number of votes for each Class A common share | Vote							1
Original issue price (per share) | $ / shares	$ 6.9475
Convertible ratio to Class A common share	1
Series C convertible preferred shares
Convertible Preferred Shares
Preferred shares designated		12,784,601
Preferred stock, shares issued (in shares)		12,784,601
Share price per share | $ / shares		$ 15.6438
Proceeds from issuance of shares | $		$ 190,822
Payment of offering expenses | $		$ 9,178
Number of votes for each Class A common share | Vote							1
Original issue price (per share) | $ / shares	$ 15.6438
Convertible ratio to Class A common share	1
Common Class A and Class B
Convertible Preferred Shares
Number of directors entitled to elect | director						1
Class A common shares
Convertible Preferred Shares
Number of shares issued on conversion of convertible preferred shares	5,546,019							5,546,019
Class B common shares
Convertible Preferred Shares
Number of shares issued on conversion of convertible preferred shares	1,070,502							1,070,502
Class A1 common shares
Convertible Preferred Shares
Number of shares issued on conversion of convertible preferred shares	12,995,954							12,995,954
Class B1 common shares
Convertible Preferred Shares
Number of shares issued on conversion of convertible preferred shares	16,057,618							16,057,618
Common Class A or Class B | Minimum
Convertible Preferred Shares
Share price per share | $ / shares						$ 15.6438
Gross proceeds from IPO | $						$ 100,000

Common Shares (Details)

Common Shares (Details) $ / shares in Units, $ in Thousands	Mar. 01, 2019USD ($)$ / sharesshares	Feb. 04, 2019USD ($)$ / sharesshares	Jun. 22, 2018USD ($)$ / sharesshares	May 29, 2018USD ($)$ / sharesshares	Dec. 31, 2019USD ($)directorVote$ / sharesshares	Dec. 31, 2018USD ($)director$ / shares	May 31, 2018$ / sharesshares	Feb. 28, 2018shares	Dec. 31, 2017$ / sharesshares
Nature of the Business and Basis of Presentation
Common share authorized (in shares)							200,000,000	44,746,463	43,918,239
Common stock, par value (in dollars per share) | $ / shares							$ 0.000273235		$ 0.000273235
Common shares or Preferred Shares not designated									11,956,456
Authorized capital							54,647,000
Preferred shares designated					0
Preferred stock, shares issued (in shares)					0
Common stock, cash dividends declared or paid | $					$ 0	$ 0
Preferred stock, cash dividends declared or paid | $						$ 0
Common Class A and Class B
Nature of the Business and Basis of Presentation
Number of directors entitled to elect | director					1
Class A common shares
Nature of the Business and Basis of Presentation
Common share authorized (in shares)								5,507,938	5,507,938
Common stock, par value (in dollars per share) | $ / shares					$ 0.000273235	$ 0.000273235
Number of shares issued on conversion of convertible preferred shares				5,546,019			5,546,019
Number of votes (per share)					1
Class B common shares
Nature of the Business and Basis of Presentation
Common share authorized (in shares)								3,568,353	3,568,353
Common stock, par value (in dollars per share) | $ / shares					$ 0.000273235	0.000273235
Number of shares issued on conversion of convertible preferred shares				1,070,502			1,070,502
Number of votes (per share)					10
Convertible ratio to Class A common share					1
Convertible ratio to Class B1 common share					1
Class A1 common shares
Nature of the Business and Basis of Presentation
Common share authorized (in shares)									0
Common stock, par value (in dollars per share) | $ / shares					$ 0.000273235	0.000273235
Number of shares issued on conversion of convertible preferred shares				12,995,954			12,995,954
Number of votes (per share) | Vote					0
Convertible ratio to Class A common share					1
Class B1 common shares
Nature of the Business and Basis of Presentation
Common share authorized (in shares)									0
Common stock, par value (in dollars per share) | $ / shares					$ 0.000273235	$ 0.000273235
Number of shares issued on conversion of convertible preferred shares				16,057,618			16,057,618
Number of votes (per share) | Vote					0
Convertible ratio to Class A common share					1
Convertible ratio to Class B common share					1
Convertible Preferred Shares (Series A, B and C)
Nature of the Business and Basis of Presentation
Preferred shares designated					0			35,670,093	22,885,492
Preferred stock, shares issued (in shares)					0
Number of directors entitled to elect | director						2
Initial Public Offering
Nature of the Business and Basis of Presentation
Aggregate proceeds from offerings net of underwriter discounts and commissions and other offering costs | $						$ 155,536
Initial Public Offering | Class A common shares
Nature of the Business and Basis of Presentation
Issuance of stock (in shares)				8,477,777
Share price (in dollars per share) | $ / shares				$ 18
Gross proceeds from IPO | $				$ 152,600
Gross proceeds from offering | $						$ 159,194
Over-allotment | Class A common shares
Nature of the Business and Basis of Presentation
Issuance of stock (in shares)	161,126		1,006,425
Share price (in dollars per share) | $ / shares	$ 18.26		$ 18
Gross proceeds from IPO | $			$ 18,116
Gross proceeds from offering | $	$ 2,942
Follow-On Public Offering and Private Placement
Nature of the Business and Basis of Presentation
Aggregate proceeds from offerings net of underwriter discounts and commissions and other offering costs | $	$ 82,988				$ 82,988
Follow-On Public Offering and Private Placement | Common Class A and Class A1 common shares
Nature of the Business and Basis of Presentation
Gross proceeds from offering | $		$ 85,000
Follow-On Offering | Class A common shares
Nature of the Business and Basis of Presentation
Issuance of stock (in shares)		2,654,984
Share price (in dollars per share) | $ / shares		$ 18.26
Gross proceeds from offering | $					$ 48,595
Private Placement | Class A1 common shares
Nature of the Business and Basis of Presentation
Issuance of stock (in shares)		2,000,000
Share price (in dollars per share) | $ / shares		$ 18.26

Share Based Compensation (Detai

Share Based Compensation (Details) $ in Thousands	Dec. 10, 2019item	May 23, 2018shares	Dec. 31, 2019shares	May 31, 2018shares	Dec. 31, 2019USD ($)shares	Dec. 31, 2018USD ($)shares
Share-based compensation
Maximum number of common shares may be issued				54,647,000
Share-based compensation expense | $					$ 15,080	$ 5,701
Stock options | Employees and Directors
Share-based compensation
Share-based compensation expense | $					13,322	5,464
Stock options | Non-employees
Share-based compensation
Share-based compensation expense | $					$ 94	$ 130
Stock options | Class A common shares
Share-based compensation
Shares outstanding (in shares)			8,491,734		8,491,734	5,960,939
Number of options granted					3,608,588
Stock options | Class A common shares | Employees and Directors
Share-based compensation
Number of options granted					3,605,388	3,114,139
Stock options | Class A common shares | Non-employees
Share-based compensation
Number of options granted					3,200	4,000
First RSU Award
Share-based compensation
Share-based compensation expense | $					$ 0
2018 Incentive Award Plan | Class A common shares
Share-based compensation
Total number of common shares authorized to issue				4,466,500
Percentage of automatic increase in shares available for issue					4.00%
Additional shares authorized					1,979,586
Number of common shares available for future grant			2,145,907		2,145,907
2018 Incentive Award Plan | Class A common shares | Maximum
Share-based compensation
Percentage of automatic increase in shares available for issue				4.00%
Maximum number of common shares may be issued				27,915,000
Rilonacept Long-term Incentive Plan
Share-based compensation
Percentage of a participant's annual target bonus for grant year represented by cash award	33.30%
Rilonacept Long-term Incentive Plan | Restricted Share Units (RSUs)
Share-based compensation
Number of grants of RSU awards that a participant may receive | item	2
Number of awards that will be earned or vest if the milestone date does not occur by the specified date | item	0
Rilonacept Long-term Incentive Plan | Restricted Share Units (RSUs) | Earnout Level 1
Share-based compensation
Potential performance earnout percentage	100.00%
Rilonacept Long-term Incentive Plan | Restricted Share Units (RSUs) | Earnout Level 2
Share-based compensation
Potential performance earnout percentage	50.00%
Rilonacept Long-term Incentive Plan | Restricted Share Units (RSUs) | Earnout Level 3
Share-based compensation
Potential performance earnout percentage	25.00%
Rilonacept Long-term Incentive Plan | Restricted Share Units (RSUs) | Earnout Level 4
Share-based compensation
Potential performance earnout percentage	0.00%
Rilonacept Long-term Incentive Plan | Restricted Share Units (RSUs) | Upside Earnout Level 1
Share-based compensation
Potential performance earnout percentage	50.00%
Rilonacept Long-term Incentive Plan | Restricted Share Units (RSUs) | Upside Earnout Level 2
Share-based compensation
Potential performance earnout percentage	25.00%
Rilonacept Long-term Incentive Plan | Restricted Share Units (RSUs) | Upside Earnout Level 3
Share-based compensation
Potential performance earnout percentage	0.00%
Rilonacept Long-term Incentive Plan | First RSU Award
Share-based compensation
Percentage of a participant's annual target bonus for grant year that each RSU grant award represents	33.30%
Vesting period	1 year
Rilonacept Long-term Incentive Plan | Second RSU Award
Share-based compensation
Percentage of a participant's annual target bonus for grant year that each RSU grant award represents	33.30%
Vesting period	2 years
2015 Equity Incentive Plan | Class A common shares
Share-based compensation
Total number of common shares authorized to issue		4,691,213	4,125,923		4,125,923
Number of shares no longer available for future grant		92,170
2015 Equity Incentive Plan | Stock options
Share-based compensation
Voting power threshold percentage used to determine the exercise price for options					10.00%
Vesting percentage of options having four year vesting term on the first anniversary of the grant date			25.00%		25.00%
Vesting percentage of options having six year vesting term on the first anniversary of the grant date			16.00%		16.00%
2015 Equity Incentive Plan | Stock options | Minimum
Share-based compensation
Vesting period					4 years
2015 Equity Incentive Plan | Stock options | Maximum
Share-based compensation
Option term of incentive awards					10 years
Option term of awards for the persons possessing more than 10% of voting power					5 years
Vesting period					6 years
2015 Equity Incentive Plan | Stock options | Class A common shares
Share-based compensation
Total number of common shares authorized to issue			0		0
Number of common shares available for future grant		0
Minimum percentage of exercise price of the fair market value of shares for the persons possessing 10% or less of voting power			100.00%		100.00%
Minimum percentage of exercise price of the fair market value of shares for the persons possessing more than 10% of voting power			110.00%		110.00%
2018 Employee Share Purchase Plan | Class A common shares
Share-based compensation
Total number of common shares authorized to issue				670,000
Automatic increase in number of shares available for issue			0
Number of common shares available for future grant			598,334		598,334
2018 Employee Share Purchase Plan | Class A common shares | Maximum
Share-based compensation
Percentage of automatic increase in shares available for issue		1.00%
Maximum number of common shares may be issued		6,420,000

Share Based Compensation - Opti

Share Based Compensation - Option valuation (Details) - Stock options	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Employees and Directors
Assumptions to determine fair value of options granted on weighted average basis:
Risk-free interest rate	2.07%	2.82%
Expected term (in years)	6 years 2 months 19 days	6 years 4 months 24 days
Expected volatility	79.14%	75.04%
Expected dividend yield	0.00%	0.00%
Non-employees
Assumptions to determine fair value of options granted on weighted average basis:
Risk-free interest rate	1.38%	2.91%
Expected term (in years)	2 years 9 months 7 days	7 years 4 months 6 days
Expected volatility	68.17%	74.18%
Expected dividend yield	0.00%	0.00%

Share Based Compensation - Op_2

Share Based Compensation - Options (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Aggregate Intrinsic Value
Proceeds from exercise of options	$ 1,119	$ 377
Class A common shares | Stock options
Number of Shares
Outstanding, beginning of the period	5,960,939
Granted	3,608,588
Exercised	(150,253)	(25,683)
Forfeited	(927,540)
Outstanding, end of the period	8,491,734	5,960,939
Options exercisable	3,373,659
Options unvested	5,118,075
Weighted Average Exercise Price
Outstanding, beginning of the period	$ 10.25
Granted	13.44
Exercised	3.93
Forfeited	15.26
Outstanding, end of the period	11.17	$ 10.25
Options exercisable	7.29
Options unvested	$ 13.74
Weighted Average Remaining Contractual Term (in years)
Outstanding	7 years 10 months 17 days	8 years 6 months 22 days
Exercisable	6 years 2 months 27 days
Unvested	8 years 11 months 16 days
Aggregate Intrinsic Value
Outstanding	$ 27,217	$ 108,352
Exercisable	19,903
Unvested	7,314
Intrinsic value of options exercised	1,776	411
Proceeds from exercise of options	$ 590	$ 87
Weighted-average grant-date fair value per share of options granted	$ 9.36	$ 11.96
Total fair value of options vested	$ 13,997	$ 2,255

Share Based Compensation - Rest

Share Based Compensation - Restricted Shares and RSUs (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)installment$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares
Share-based compensation
Share-based compensation expense | $	$ 15,080	$ 5,701
Restricted shares
Weighted Average Fair Value at Issuance
Aggregate fair value of vested restricted shares | $	$ 12,154	$ 15,182
Restricted shares | Class A common shares
Share-based compensation
Vesting period	4 years
Number of shares
Beginning of the period	133,812
Vested	(133,812)
End of the period		133,812
Weighted Average Fair Value at Issuance
Beginning of the period | $ / shares	$ 0.000273235
Vested | $ / shares	$ 0.000273235
End of the period | $ / shares		$ 0.000273235
Restricted shares | Class B common shares
Share-based compensation
Vesting period	4 years
Number of shares
Beginning of the period	743,407
Vested	(743,407)
End of the period		743,407
Weighted Average Fair Value at Issuance
Beginning of the period | $ / shares	$ 0.000273235
Vested | $ / shares	$ 0.000273235
End of the period | $ / shares		$ 0.000273235
Restricted Share Units (RSUs)
Share-based compensation
Number of Class A common shares received per award upon vesting	1
Number of shares
Granted	328,296
End of the period	328,296
Weighted Average Fair Value at Issuance
Granted | $ / shares	$ 12.93
End of the period | $ / shares	$ 12.93
Time-based RSUs
Share-based compensation
Number of vesting installments | installment	1
Grant date fair value awards granted | $	$ 1,250
Share-based compensation expense | $	$ 65
First RSU Award
Share-based compensation
Number of awards that will vest in the event performance goals are not achieved	0
Grant date fair value awards granted | $	$ 2,994
Share-based compensation expense | $	$ 0

Share Based Compensation - Clas

Share Based Compensation - Classification of expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-based compensation
Share-based compensation expense	$ 15,080	$ 5,701
Expenses expected to be recognized over a weighted average remaining period		3 years 1 month 6 days
Research and development expenses
Share-based compensation
Share-based compensation expense	5,746	$ 2,285
General and administrative expenses
Share-based compensation
Share-based compensation expense	9,334	$ 3,416
Stock options
Share-based compensation
Total unrecognized compensation cost	$ 44,185
Expenses expected to be recognized over a weighted average remaining period	3 years 1 month 6 days
Time-based RSUs
Share-based compensation
Share-based compensation expense	$ 65
Total unrecognized compensation cost	$ 1,185
Expenses expected to be recognized over a weighted average remaining period	1 year
First RSU Award
Share-based compensation
Share-based compensation expense	$ 0
Total unrecognized compensation cost	$ 2,994

License and Acquisition Agree_2

License and Acquisition Agreements - Biogen Asset Purchase Agreement (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
License and Acquisition Agreements
Accrued milestones			$ 15,000
Research and development expense		$ 135,001	$ 86,597
Biogen
License and Acquisition Agreements
Research and development expense		10,347
Asset Purchase Agreement | Biogen
License and Acquisition Agreements
Upfront payment for exchange of rights	$ 11,500
Technology transfer payment	500
Milestone payment upon achievement of clinical milestone event		$ 10,000		$ 4,000
One-time payment of upfront sublicense fee on retained contracts	150
Maximum aggregate obligation to pay insignificant annual maintenance fees as well as clinical and regulatory milestone payments	$ 1,575
Notice period to terminate the agreement	90 days
Uncured period which causes termination of the agreement, due to insolvency or bankruptcy or for material breach of the agreement by the other party that remains uncured	90 days
Notice period to terminate the agreement under payment-related breaches	30 days
Asset Purchase Agreement | Biogen | Maximum
License and Acquisition Agreements
Milestone payment to be paid upon clinical and regulatory milestone achievement	$ 179,000
Milestone payment to be paid upon net sales milestone achievement	$ 150,000

License and Acquisition Agree_3

License and Acquisition Agreements - Novo Nordisk License Agreement (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Aug. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
License and Acquisition Agreements
Milestone payments due		$ 0	$ 0
Research and development expense		135,001	86,597
License Agreement | Novo Nordisk
License and Acquisition Agreements
Upfront payment for exchange of rights	$ 1,500
Consideration payable upon completion of technology transfer	150
Milestone payment payable after achievement of specified milestones	$ 1,000
Research and development expense		$ 0	$ 154

License and Acquisition Agree_4

License and Acquisition Agreements - Primatope Stock Purchase Option Agreement (Details) $ in Thousands	1 Months Ended		12 Months Ended
	Mar. 31, 2019USD ($)	Sep. 30, 2017USD ($)item	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Jun. 30, 2019USD ($)
License and Acquisition Agreements
Accrued milestones				$ 15,000
Research and development expense			$ 135,001	86,597
Primatope | Stock Option Purchase Agreement
License and Acquisition Agreements
Percentage of capital stock available to purchase in call option		100.00%
Upfront payment for initial option period		$ 500
Payment for extension of option period				800
Research and development expense				$ 800
Primatope Acquisition
License and Acquisition Agreements
Purchase price	$ 18,000
Upfront consideration payable on exercise of call option to acquire all outstanding equity	10,000
Milestone payment payable after achievement of specified milestones	$ 5,000				$ 3,000
Research and development expense			$ 18,000
Maximum | Primatope | Stock Option Purchase Agreement
License and Acquisition Agreements
Number of extensions allowed for initial option period | item		3
Total aggregate extension payments		$ 800

License and Acquisition Agree_5

License and Acquisition Agreements - Beth Israel Deaconess Medical Center License Agreement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
License and Acquisition Agreements
Research and development expense	$ 135,001	$ 86,597
License Agreement | BIDMC
License and Acquisition Agreements
Research and development expense	10
License Agreement | BIDMC | Maximum
License and Acquisition Agreements
Milestone payment to be paid upon clinical and regulatory milestone achievement	$ 1,200

License and Acquisition Agree_6

License and Acquisition Agreements - Regeneron License Agreement (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2019	Dec. 31, 2018
License and Acquisition Agreements
Research and development expense		$ 135,001	$ 86,597
Regeneron | License Agreement
License and Acquisition Agreements
Upfront payment for exchange of rights	$ 5,000
Uncured period which causes termination of the agreement, due to insolvency or bankruptcy or for material breach of the agreement by the other party that remains uncured	90 days
Research and development expense			0
Notice period to terminate the agreement under payment-related breaches	30 days
Consecutive suspension of activities period for termination of agreement	12 months
Period after which the agreement can be terminated	18 months
Notice period to terminate the agreement	180 days
Notice period to terminate the agreement after US marketing approval of the developed product	1 year
Notice period to terminate the agreement if products are having safety concerns	3 months
Regeneron | Clinical Supply Agreement
License and Acquisition Agreements
Research and development expense related to purchase of drug materials		$ 6,854	$ 1,835
Maximum | Regeneron | License Agreement
License and Acquisition Agreements
Milestone payment to be paid upon regulatory milestone achievement	$ 27,500

License and Acquisition Agree_7

License and Acquisition Agreements - MedImmune License Agreement (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
License and Acquisition Agreements
Accrued milestone payments			$ 15,000
Research and development expense		$ 135,001	86,597
MedImmune | License Agreement
License and Acquisition Agreements
Upfront payment for exchange of rights	$ 8,000
Milestone payment to be paid upon regulatory milestone achievement	10,000
Accrued milestone payments	10,000		5,000
Payment of accrued milestones		10,000
Pass-through payment paid upon clinical milestone achievement		5,000
Annual net sales excluded from calculation of specified annual net sales thresholds	$ 1,000,000
Maximum percentage of royalty payable on annual net sales of licensed products	20.00%
Notice period to terminate the agreement by both parties for material breaches	90 days
Notice period to terminate the agreement	90 days
Research and development expense		$ 0	$ 5,000
Minimum | MedImmune | License Agreement
License and Acquisition Agreements
Additional specified annual net sales threshold for additional milestone payment.	$ 1,000,000
Maximum | MedImmune | License Agreement
License and Acquisition Agreements
Milestone payment to be paid upon specified milestone achievements for first two indications	72,500
Milestone payment to be paid upon clinical and regulatory milestone achievement	15,000
Milestone payment to be paid upon specified annual sales milestone achievements	85,000
Additional milestone payments payable after achievement of additional annual sales	$ 1,100,000

License and Acquisition Agree_8

License and Acquisition Agreements - Kite Clinical Collaboration Agreement (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
License and Acquisition Agreements
Research and development expense		$ 135,001	$ 86,597
Clinical Collaboration Agreement | Kite
License and Acquisition Agreements
Term of agreement	1 year
Research and development expense		$ 0

Income Taxes (Details)

Income Taxes (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)subsidiary	Dec. 31, 2018USD ($)
Bermuda statutory income tax rate	0.00%	0.00%
Income tax benefits - Bermuda	$ 0	$ 0
Net operating loss carryforwards - Bermuda	$ 0	$ 0
Kiniksa UK
Number of subsidiaries | subsidiary	2

Income Taxes - Components of in

Income Taxes - Components of income tax provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income (loss) before provision for income taxes
Bermuda	$ (168,053)	$ (105,562)
Income (loss) before provision for income taxes	(163,914)	(103,441)
Current income tax (provision):
Total current income tax (provision)	(1,109)	(764)
Deferred income tax benefit:
Total deferred income tax benefit	3,156	978
Total provision (benefit) for income taxes	2,047	214
U.S., U.K., Germany, and France
Income (loss) before provision for income taxes
Foreign	4,139	2,121
U.S.
Current income tax (provision):
U.S. federal	(567)	(547)
U.S. state	(530)	(217)
Deferred income tax benefit:
U.S. federal	2,397	542
U.S. state	759	$ 436
U.K., Germany, and France
Current income tax (provision):
Foreign	$ (12)

Income Taxes - Reconciliation (

Income Taxes - Reconciliation (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Taxes
Bermuda statutory income tax rate	0.00%	0.00%
Foreign (U.S.) tax rate differential	(0.50%)	(1.00%)
Research and development tax credits	2.20%	1.50%
Share-based compensation	(0.50%)	0.10%
Permanent differences	(0.10%)
Change in valuation allowance	(0.10%)
U.S. state taxes, net of federal	(0.30%)	(0.40%)
FDII	0.90%
Uncertain tax positions	(0.30%)
Effective income tax rate	1.30%	0.20%

Income Taxes - Components of de

Income Taxes - Components of deferred tax assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes
Research and development tax credit carryforwards	$ 238	$ 75
Depreciation and amortization	(745)	(639)
Share-based compensation	3,746	1,000
Accrued expenses and other	1,273	829
Net operating losses	190
Total deferred tax assets	4,702	1,265
Valuation allowance	(330)	(49)	$ (27)
Net deferred tax assets	4,372	1,216
Foreign | U.S.
Income Taxes
Net operating losses	228	0
State | U.S.
Income Taxes
Research and development tax credit carryforwards	$ 265	$ 95

Income Taxes - Valuation allowa

Income Taxes - Valuation allowances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Taxes
Valuation allowance at beginning of year	$ (49)	$ (27)
Increases recorded to through the balance sheet	(200)
Increases recorded to income tax provision	(81)	(22)
Valuation allowance at end of year	(330)	$ (49)
Aggregate valuation allowance increase	$ (281)

Income Taxes - Uncertainties in

Income Taxes - Uncertainties in Income Tax Provision Liability (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)item	Dec. 31, 2018USD ($)
Unrecognized tax benefits
Unrecognized tax benefits, beginning balance	$ 0
Gross increases based on current period tax positions	528
Unrecognized tax benefits, ending balance	$ 528
Accrued interest or penalties related to uncertain tax positions		$ 0
Number of income tax examinations pending | item	0

Net Loss per Share (Details)

Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net loss attributable to common shareholders	$ (161,867)	$ (103,227)
Denominator:
Weighted average common shares outstanding — basic and diluted	54,049,477	29,547,427
Net loss per share attributable to common shareholders — basic and diluted	$ (2.99)	$ (3.49)

Net Loss per Share - Anti-dilut

Net Loss per Share - Anti-dilutive securities (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Anti-dilutive securities excluded from computation of earnings per share
Total, anti-dilutive securities excluded from computation of earnings per share	8,820,030	6,838,158
Stock options
Anti-dilutive securities excluded from computation of earnings per share
Total, anti-dilutive securities excluded from computation of earnings per share	8,491,734	5,960,939
Restricted shares
Anti-dilutive securities excluded from computation of earnings per share
Total, anti-dilutive securities excluded from computation of earnings per share		877,219
Restricted Share Units (RSUs)
Anti-dilutive securities excluded from computation of earnings per share
Total, anti-dilutive securities excluded from computation of earnings per share	328,296

Commitments and Contingencies (

Commitments and Contingencies (Details) $ in Thousands	Dec. 31, 2019USD ($)
Manufacturing commitments
Non-cancelable purchase commitments	$ 2,863
Rilonacept Long-term Incentive Plan | First RSU Award
Long-term incentive plan
Estimated amount of cash award in the event performance goals are achieved	$ 2,083

Benefit Plans (Details)

Benefit Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Benefit Plans
Matching contributions by the Company for first 3% of each participant's salary contributed (as a percent)	100.00%
Percentage of employees' salary contributed matched 100% by employer	3.00%
Matching contributions by the Company for next 2% of each participant's salary contributed (as a percent)	50.00%
Percentage of employees' salary contributed matched 50% by employer	2.00%
Contributions made by the Company to defined contribution savings plan	$ 851	$ 315