Keros Therapeutics (KROS) 10-Q 10 Nov 20 2020 Q3 Quarterly report Financial data

Cover

Cover - shares	9 Months Ended
	Sep. 30, 2020	Nov. 03, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2020
Document Transition Report	false
Entity File Number	001-39264
Entity Registrant Name	KEROS THERAPEUTICS, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	81-1173868
Entity Address, Address Line One	99 Hayden Avenue
Entity Address, Address Line Two	Suite 120
Entity Address, Address Line Three	Building E
Entity Address, City or Town	Lexington
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02421
City Area Code	617
Local Phone Number	314-6297
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	KROS
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		20,188,351
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Entity Central Index Key	0001664710

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
CURRENT ASSETS:
Cash and cash equivalents	$ 133,810	$ 7,020
Prepaid expenses and other current assets	2,606	381
Deferred IPO costs	0	604
Research and development incentive receivable	0	922
Total current assets	136,416	8,927
Operating lease right-of-use assets	976	1,205
Property and equipment, net	739	708
Restricted cash	115	115
TOTAL ASSETS	138,246	10,955
CURRENT LIABILITIES:
Accounts payable	1,716	2,088
Current portion of operating lease liabilities	412	376
Accrued expenses and other current liabilities	4,697	2,022
Total current liabilities	6,825	4,486
Operating lease liabilities, net of current portion	586	899
Preferred stock tranche liability	0	4,956
Other liabilities	77	119
Total liabilities	7,488	10,460
Convertible preferred stock, carrying amount		19,941
STOCKHOLDERS' EQUITY (DEFICIT):
Common stock, value, issued	2	1
Additional paid-in capital	185,091	203
Accumulated deficit	(54,335)	(19,650)
Total stockholders' equity (deficit)	130,758	(19,446)
TOTAL LIABILITIES, CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT)	138,246	10,955
Series A Preferred Stock
CURRENT LIABILITIES:
Convertible preferred stock, carrying amount	0	9,891
Series A-1 Preferred Stock
CURRENT LIABILITIES:
Convertible preferred stock, carrying amount	0	944
Series B-1 Preferred Stock
CURRENT LIABILITIES:
Convertible preferred stock, carrying amount	$ 0	$ 9,106

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Shares authorized (in shares)		17,289,895
Preferred stock, shares issued (in shares)		6,555,307
Preferred stock, shares outstanding (in shares)		6,555,307
LIQUIDATION VALUE		$ 26,038
Common stock, par value (USD per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	200,000,000	27,000,000
Common stock, shares issued (in shares)	20,185,730	2,429,705
Common stock, shares outstanding (in shares)	20,185,730	2,429,705
Series A Preferred Stock
Par value (USD per share)	$ 0.0001	$ 0.0001
Shares authorized (in shares)	0	10,000,000
Preferred stock, shares issued (in shares)	0	4,607,652
Preferred stock, shares outstanding (in shares)	0	4,607,652
LIQUIDATION VALUE	$ 0	$ 12,271
Series A-1 Preferred Stock
Par value (USD per share)	$ 0.0001	$ 0.0001
Shares authorized (in shares)	0	800,000
Preferred stock, shares issued (in shares)	0	368,612
Preferred stock, shares outstanding (in shares)	0	368,612
LIQUIDATION VALUE	$ 0	$ 1,171
Series B-1 Preferred Stock
Par value (USD per share)	$ 0.0001	$ 0.0001
Shares authorized (in shares)	0	3,427,004
Preferred stock, shares issued (in shares)	0	1,579,043
Preferred stock, shares outstanding (in shares)	0	1,579,043
LIQUIDATION VALUE	$ 0	$ 12,596

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
REVENUE:
Research collaboration revenue	$ 0	$ 2,500	$ 0	$ 7,500
OPERATING EXPENSES:
Research and development	(8,395)	(3,854)	(24,186)	(13,218)
General and administrative	(3,553)	(972)	(9,180)	(2,117)
Total operating expenses	(11,948)	(4,826)	(33,366)	(15,335)
LOSS FROM OPERATIONS	(11,948)	(2,326)	(33,366)	(7,835)
OTHER INCOME (EXPENSE), NET
Interest expense, net	(2)	(3)	(5)	(7)
Research and development incentive income	0	0	0	558
Change in fair value of preferred stock tranche obligation	0	(1,235)	(1,490)	(2,486)
Other income (expense), net	(86)	15	4	185
Total other income (expense), net	(88)	(1,223)	(1,491)	(1,750)
Loss before income taxes	(12,036)	(3,549)	(34,857)	(9,585)
Income tax benefit	0	0	172	0
Net loss	(12,036)	(3,549)	(34,685)	(9,585)
Net loss attributable to common stockholders—basic and diluted (Note 10)	$ (12,036)	$ (3,999)	$ (35,697)	$ (10,935)
Net loss per share attributable to common stockholders - basic and diluted (USD per share)	$ (0.60)	$ (1.71)	$ (2.65)	$ (4.76)
Weighted-average common stock outstanding - basic and diluted (in shares)	20,175,883	2,342,782	13,452,606	2,296,701

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders’ Deficit - USD ($) $ in Thousands	Total	Common Stock	ADDITIONAL PAID-IN CAPITAL	ACCUMULATED DEFICIT	Series A Preferred Stock	Series A-1 Preferred Stock	Series B-1 Preferred Stock	Series C preferred stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Ending balance (in shares)		2,243,648
Ending balance	$ (7,183)	$ 1	$ 130	$ (7,314)
Beginning balance (in shares) at Dec. 31, 2018					4,607,652	368,612	1,579,043	0
Beginning balance at Dec. 31, 2018					$ 9,891	$ 944	$ 9,106	$ 0
Ending balance (in shares) at Mar. 31, 2019					4,607,652	368,612	1,579,043	0
Ending balance at Mar. 31, 2019					$ 9,891	$ 944	$ 9,106	$ 0
Beginning balance (in shares) at Dec. 31, 2018		2,243,648
Beginning balance at Dec. 31, 2018	(7,183)	$ 1	130	(7,314)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock (in shares)		25,918
Vesting of restricted stock	0
Stock-based compensation	11		11
Net loss	(3,183)			(3,183)
Ending balance (in shares)		2,243,648
Ending balance	(7,183)	$ 1	130	(7,314)
Beginning balance (in shares) at Dec. 31, 2018					4,607,652	368,612	1,579,043	0
Beginning balance at Dec. 31, 2018					$ 9,891	$ 944	$ 9,106	$ 0
Ending balance (in shares) at Sep. 30, 2019					4,607,652	368,612	1,579,043	0
Ending balance at Sep. 30, 2019					$ 9,891	$ 944	$ 9,106	$ 0
Beginning balance (in shares) at Dec. 31, 2018		2,243,648
Beginning balance at Dec. 31, 2018	(7,183)	$ 1	130	(7,314)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(9,585)
Ending balance (in shares)		2,243,648
Ending balance	(7,183)	$ 1	130	(7,314)
Ending balance (in shares)		2,269,566
Ending balance	(10,355)	$ 1	141	(10,497)
Beginning balance (in shares) at Mar. 31, 2019					4,607,652	368,612	1,579,043	0
Beginning balance at Mar. 31, 2019					$ 9,891	$ 944	$ 9,106	$ 0
Ending balance (in shares) at Jun. 30, 2019					4,607,652	368,612	1,579,043	0
Ending balance at Jun. 30, 2019					$ 9,891	$ 944	$ 9,106	$ 0
Beginning balance (in shares) at Mar. 31, 2019		2,269,566
Beginning balance at Mar. 31, 2019	(10,355)	$ 1	141	(10,497)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)		22,029
Exercise of common stock options	3		3
Vesting of restricted stock (in shares)		25,918
Vesting of restricted stock	0
Stock-based compensation	13		13
Net loss	(2,853)			(2,853)
Ending balance (in shares)		2,269,566
Ending balance	(10,355)	$ 1	141	(10,497)
Ending balance (in shares)		2,317,513
Ending balance	(13,192)	$ 1	157	(13,350)
Ending balance (in shares) at Sep. 30, 2019					4,607,652	368,612	1,579,043	0
Ending balance at Sep. 30, 2019					$ 9,891	$ 944	$ 9,106	$ 0
Beginning balance (in shares) at Jun. 30, 2019		2,317,513
Beginning balance at Jun. 30, 2019	(13,192)	$ 1	157	(13,350)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)		46,912
Exercise of common stock options	7		7
Vesting of restricted stock (in shares)		25,918
Vesting of restricted stock	0
Stock-based compensation	17		17
Net loss	(3,549)			(3,549)
Ending balance (in shares)		2,317,513
Ending balance	(13,192)	$ 1	157	(13,350)
Ending balance (in shares)		2,390,343
Ending balance	(16,717)	$ 1	181	(16,899)
Ending balance (in shares)		2,429,705
Ending balance	$ (19,446)	$ 1	203	(19,650)
Beginning balance (in shares) at Dec. 31, 2019	6,555,307				4,607,652	368,612	1,579,043	0
Beginning balance at Dec. 31, 2019	$ 19,941				$ 9,891	$ 944	$ 9,106	$ 0
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of series C convertible preferred stock, net of issuance costs of $219 (in shares)								4,169,822
Issuance of Series C convertible preferred stock, net of issuance costs of $219	0							$ 55,781
Ending balance (in shares) at Mar. 31, 2020					4,607,652	368,612	1,579,043	4,169,822
Ending balance at Mar. 31, 2020					$ 9,891	$ 944	$ 9,106	$ 55,781
Beginning balance (in shares) at Dec. 31, 2019		2,429,705
Beginning balance at Dec. 31, 2019	(19,446)	$ 1	203	(19,650)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)		44,686
Exercise of common stock options	13		13
Vesting of restricted stock (in shares)		17,279
Vesting of restricted stock	0
Stock-based compensation	12		12
Settlement of preferred stock tranche liability	6,446		6,446
Net loss	(11,892)			(11,892)
Ending balance (in shares)		2,429,705
Ending balance	$ (19,446)	$ 1	203	(19,650)
Beginning balance (in shares) at Dec. 31, 2019	6,555,307				4,607,652	368,612	1,579,043	0
Beginning balance at Dec. 31, 2019	$ 19,941				$ 9,891	$ 944	$ 9,106	$ 0
Ending balance (in shares) at Sep. 30, 2020					0	0	0	0
Ending balance at Sep. 30, 2020					$ 0	$ 0	$ 0	$ 0
Beginning balance (in shares) at Dec. 31, 2019		2,429,705
Beginning balance at Dec. 31, 2019	$ (19,446)	$ 1	203	(19,650)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)	96,339
Net loss	$ (34,685)
Ending balance (in shares)		2,429,705
Ending balance	(19,446)	$ 1	203	(19,650)
Ending balance (in shares)		2,491,670
Ending balance	(24,867)	$ 1	6,674	(31,542)
Beginning balance (in shares) at Mar. 31, 2020					4,607,652	368,612	1,579,043	4,169,822
Beginning balance at Mar. 31, 2020					$ 9,891	$ 944	$ 9,106	$ 55,781
Ending balance (in shares) at Jun. 30, 2020					0	0	0	0
Ending balance at Jun. 30, 2020					$ 0	$ 0	$ 0	$ 0
Beginning balance (in shares) at Mar. 31, 2020		2,491,670
Beginning balance at Mar. 31, 2020	(24,867)	$ 1	6,674	(31,542)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Offering expenses associated with direct offering	(8)		(8)
Conversion of convertible preferred stock upon initial public offering (in shares)		10,725,129			(4,607,652)	(368,612)	(1,579,043)	(4,169,822)
Conversion of convertible preferred stock upon initial public offering	75,722	$ 1	75,721		$ (9,891)	$ (944)	$ (9,106)	$ (55,781)
Initial public offering, net of underwriting discounts, commissions and offering costs (in shares)		6,900,000
Initial public offering, net of underwriting discounts, commissions and offering costs	100,123		100,123
Exercise of common stock options (in shares)		24,003
Exercise of common stock options	9		9
Vesting of restricted stock (in shares)		17,278
Vesting of restricted stock	0
Stock-based compensation	1,139		1,139
Net loss	(10,757)			(10,757)
Ending balance (in shares)		2,491,670
Ending balance	(24,867)	$ 1	6,674	(31,542)
Ending balance (in shares)		20,158,080
Ending balance	141,361	$ 2	183,658	(42,299)
Ending balance (in shares) at Sep. 30, 2020					0	0	0	0
Ending balance at Sep. 30, 2020					$ 0	$ 0	$ 0	$ 0
Beginning balance (in shares) at Jun. 30, 2020		20,158,080
Beginning balance at Jun. 30, 2020	141,361	$ 2	183,658	(42,299)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)		27,650
Exercise of common stock options	9		9
Vesting of restricted stock	0
Stock-based compensation	1,424		1,424
Net loss	(12,036)			(12,036)
Ending balance (in shares)		20,158,080
Ending balance	141,361	$ 2	183,658	(42,299)
Ending balance (in shares)		20,185,730
Ending balance	$ 130,758	$ 2	$ 185,091	$ (54,335)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Deficit (Parenthetical) - USD ($) $ in Thousands	Mar. 02, 2020	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Common stock, par value (USD per share)			$ 0.0001	$ 0.0001	$ 0.0001
Issuance costs		$ 219	$ 227	$ 0
Series A Preferred Stock
Par value (USD per share)			$ 0.0001	$ 0.0001	0.0001
Series A-1 Preferred Stock
Par value (USD per share)			0.0001	0.0001	0.0001
Series B-1 Preferred Stock
Par value (USD per share)			0.0001	0.0001	$ 0.0001
Series C preferred stock
Par value (USD per share)	$ 0.0001		$ 0.0001	$ 0.0001
Issuance costs	$ 200

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (12,036)	$ (11,892)	$ (3,549)	$ (3,183)	$ (34,685)	$ (9,585)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation expense					203	149
Stock-based compensation expense					2,575	41
Non-cash lease expense					229	(558)
Changes in fair value of preferred stock tranche obligation	0		1,235		1,490	2,486
Changes in operating assets and liabilities:
Research and development incentive receivable					922	(518)
Prepaid expenses and other current assets					(2,225)	1,860
Deferred IPO costs					604	(18)
Accounts payable					(372)	1,442
Operating lease liabilities					(277)	574
Deferred revenue					0	(7,500)
Accrued expenses and other current liabilities					2,675	1,165
Other liabilities					(42)	(38)
Net cash used in operating activities					(28,903)	(10,500)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment					(234)	(253)
Net cash used in investing activities					(234)	(253)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of Series C preferred stock					56,000	0
Payment of Series C preferred stock issuance costs		(219)			(227)	0
Proceeds from issuance of common stock from the initial public offering, net of underwriting discounts of $7,728					102,672	0
Payment of initial public offering costs					(2,549)	0
Proceeds from exercise of stock options					31	10
Net cash provided by financing activities					155,927	10
NET INCREASE (DECREASE) IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH					126,790	(10,743)
Cash, cash equivalents and restricted cash at beginning of period		7,135		23,390	7,135	23,390	$ 23,390
Cash, cash equivalents and restricted cash at end of period	133,925		12,647		133,925	12,647	7,135
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Settlement of preferred stock tranche obligation					6,446	0
Conversion of preferred stock into common stock upon closing of initial public offering					75,714	0
Reconciliation of cash, cash equivalents and restricted cash
Cash and cash equivalents								$ 133,810	$ 7,020	$ 12,532
Restricted cash								115		115
Total cash, cash equivalents and restricted cash	$ 133,925	$ 7,135	$ 12,647	$ 23,390	$ 133,925	$ 12,647	$ 23,390	$ 133,925	$ 7,135	$ 12,647

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows (Parenthetical) $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Statement of Cash Flows [Abstract]
Issuance costs	$ 7,728

Nature of Business and Basis of

Nature of Business and Basis of Presentation	9 Months Ended
	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business and Basis of Presentation	NATURE OF BUSINESS AND BASIS OF PRESENTATION Keros Therapeutics, Inc. (“Keros” or the “Company”) was incorporated in 2015 as a Delaware corporation. Its principal offices are in Lexington, Massachusetts. The Company is a clinical-stage biopharmaceutical company focused on the discovery, development and commercialization of novel treatments for patients suffering from hematological and musculoskeletal disorders with high unmet medical need. The accompanying unaudited interim condensed consolidated financial statements are prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and include the accounts of the Company and its wholly owned Australian subsidiary, Keros Therapeutics Australia Pty Ltd (“Keros Australia”). All significant intercompany transactions and accounts have been eliminated in consolidation. Since its inception in 2015, the Company has devoted the majority of its resources on business planning, research and development of its product candidates, including by conducting clinical trials and preclinical studies, raising capital and recruiting management and technical staff to support these operations. To date, the Company has not generated any revenue from product sales as none of its product candidates have been approved for commercialization. On April 13, 2020, the Company completed an initial public offering (“IPO”) in which the Company issued and sold 6,900,000 shares of its common stock, which includes 900,000 shares issued and sold pursuant to the full exercise of the underwriters’ option to purchase additional shares, at a public offering price of $16.00 per share, for aggregate gross proceeds of $110.4 million. The Company received approximately $100.1 million in net proceeds after deducting underwriting discounts and commissions and offering costs. In connection with the IPO, the Company's board of directors (the "Board") and stockholders approved an amended and restated certificate of incorporation to, among other things, effect a one-for-2.1703 reverse stock split of its issued and outstanding shares of common stock and convertible preferred stock, as well as to effect a proportional adjustment to the existing conversion ratios for the Company’s convertible preferred stock. The reverse stock split was effected on March 31, 2020. Accordingly, all share and per share amounts of common stock for all periods presented in the accompanying unaudited interim condensed consolidated financial statements and notes thereto have been retroactively adjusted, where applicable, to reflect this reverse stock split and adjustment of preferred stock conversion ratios. Upon the closing of the IPO, all of the then-outstanding shares of convertible preferred stock automatically converted into 10,725,129 shares of common stock at the applicable conversion ratio then in effect. Subsequent to the closing of the IPO, there were no shares of convertible preferred stock outstanding. The Company’s condensed consolidated financial statements have been prepared on the basis of the Company continuing as a going concern for the next 12 months. Management believes that the Company’s existing cash and cash equivalents, will allow the Company to continue its operations for at least the next 12 months. In the absence of a significant source of recurring revenue, the continued viability of the Company beyond that point is dependent on its ability to continue to raise additional capital to finance its operations. If the Company is unable to obtain additional funding, the Company may be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects, or the Company may be unable to continue operations. The accompanying unaudited interim condensed consolidated financial statements as of September 30, 2020 and for the three and nine months ended September 30, 2020 and 2019 have been prepared by the Company in conformity with generally accepted accounting principles in the United States of America (“U.S. GAAP”) and, pursuant to the rules and regulations of Article 10 of Regulation S-X of the Securities Act published by the Securities and Exchange Commission (“SEC”) for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with U.S. GAAP have been condensed or omitted pursuant to such rules and regulations. However, the Company believes the disclosures are adequate. These unaudited interim condensed consolidated financial statements should be read in conjunction with the Company’s audited financial statements and notes thereto for the year ended December 31, 2019 included in the Company’s final prospectus that forms part of the Company’s Registration Statement on Form S-1 (Reg. No. 333-237212), filed with the SEC pursuant to Rule 424(b)(4) on April 8, 2020 (the “Prospectus”). The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited financial statements. In the opinion of management, the accompanying unaudited interim condensed consolidated financial statements contain all adjustments which are necessary for a fair presentation of the Company’s condensed consolidated balance sheets as of September 30, 2020 and December 31, 2019, condensed consolidated statements of operations for the three and nine months ended September 30, 2020 and 2019 and condensed consolidated cash flows for the nine months ended September 30, 2020 and 2019. Such adjustments are of a normal and recurring nature. The results of operations for the three and nine months ended September 30, 2020 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2020.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Significant Accounting Policies The significant accounting policies and estimates used in preparation of the unaudited interim condensed consolidated financial statements are described in the Company’s audited consolidated financial statements as of and for the year ended December 31, 2019, and the notes thereto, which are included in the Company’s Prospectus. Except as detailed below, there have been no material changes to the Company’s significant accounting policies during the nine months ended September 30, 2020. Risks and Uncertainties With the global COVID-19 pandemic continuing throughout 2020, the Company has implemented business continuity plans designed to address and mitigate the impact of the COVID-19 pandemic on its employees and its business operations, including its preclinical studies and clinical trials, supply chains and third-party providers. Additionally, in response to the spread of COVID-19, the Company closed its principal executive office in March 2020, with its administrative employees continuing their work outside of the office, and limited the number of staff in any given research laboratory. The Company anticipates that the COVID-19 pandemic will have an impact on the development timelines for several of its preclinical and clinical programs. The extent to which the COVID-19 pandemic impacts the Company’s business, its clinical development and regulatory efforts, its corporate development objectives and the value of and market for its common stock will depend on future developments which are highly uncertain and cannot be predicted with confidence at this time, such as the ultimate duration of the pandemic, travel restrictions, quarantines, social distancing and business closure requirements in the United States, Australia, New Zealand and other countries and the effectiveness of actions taken globally to contain and treat the disease. The global economic slowdown, the overall disruption of global healthcare systems and the other risks and uncertainties associated with the pandemic could have a material adverse effect on the Company’s business, financial condition, results of operations and growth prospects. As of the date of issuance of these financial statements, the Company is not aware of any specific event or circumstance that would require the Company to update its estimates, assumptions and judgments or revise the carrying value of its assets or liabilities. Actual results could differ from those estimates, and any such differences may be material to the Company’s financial statements. In addition, the Company is subject to other challenges and risks specific to its business and its ability to execute on its business plan and strategy, as well as risks and uncertainties common to companies in the biopharmaceutical industry with research and development operations, including, without limitation, risks and uncertainties associated with: obtaining regulatory approval of its product candidates; delays or problems in obtaining clinical supply, loss of single source suppliers or failure to comply with manufacturing regulations; product development and the inherent uncertainty of clinical success; the challenges of protecting and enhancing its intellectual property rights; the challenges of complying with applicable regulatory requirements; and identifying, acquiring or in-licensing additional products or product candidates. In addition, to the extent the ongoing COVID-19 pandemic adversely affects the Company’s business and results of operations, it may also have the effect of heightening many of the other risks and uncertainties discussed above. Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ deficit as a reduction of proceeds generated as a result of the offering. Should a planned equity financing be abandoned, the deferred offering costs would be expensed immediately as a charge to operating expenses in the condensed consolidated statement of operations. Upon closing the IPO in April 2020, deferred offering costs were reclassified to additional paid-in capital, representing a reduction in IPO proceeds. As of September 30, 2020 and December 31, 2019, the Company had deferred offering costs of $0 and $0.6 million, respectively. Recently Issued Accounting Pronouncements The new accounting pronouncements recently adopted by the Company and issued by the Financial Accounting Standards Board ("FASB") that are applicable to the Company are described in the Company’s audited financial statements as of and for the year ended December 31, 2019, and the notes thereto, which are included in the Company’s Prospectus filed with the SEC on April 8, 2020. There have been no new accounting pronouncements issued in the nine months ended September 30, 2020 that are applicable to the Company.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	FAIR VALUE MEASUREMENTS The following table presents information about the Company’s financial assets and liabilities measured at fair value on a recurring basis and indicates the level of the fair value hierarchy utilized to determine such fair values (in thousands): DESCRIPTION SEPTEMBER 30, 2020 QUOTED PRICES ACTIVE MARKETS FOR IDENTICAL ASSETS SIGNIFICANT OTHER OBSERVABLE INPUTS SIGNIFICANT OTHER OBSERVABLE INPUTS Asset Money market funds $ 128,668 $ 128,668 $ — $ — Total financial assets $ 128,668 $ 128,668 $ — $ — DESCRIPTION DECEMBER 31, 2019 QUOTED PRICES ACTIVE MARKETS FOR IDENTICAL ASSETS (LEVEL 1) SIGNIFICANT OTHER OBSERVABLE INPUTS (LEVEL 2) SIGNIFICANT OTHER OBSERVABLE INPUTS (LEVEL 3) Asset Money market funds $ 4,972 $ 4,972 $ — $ — Total financial assets $ 4,972 $ 4,972 $ — $ — Liability Preferred stock tranche obligation $ (4,956) $ — $ — $ (4,956) Total financial liabilities $ (4,956) $ — $ — $ (4,956) There have been no transfers between fair value levels during the nine months ended September 30, 2020. Prior to settlement, the Company’s Preferred Stock Tranche Obligation (defined below) was carried at fair value determined according to Level 3 inputs in the fair value hierarchy as described below. The carrying values of other current assets, accounts payable and accrued expenses approximate their fair values due to the short-term nature of these assets and liabilities. Preferred Stock Tranche Obligation The Company determined that its obligation to issue, and the Company’s investors’ obligation to purchase additional shares of convertible preferred stock at a fixed price (i.e. the issuance price) in subsequent tranches following the initial closings of the series A, series A-1, and series B-1 convertible preferred stock (respectively, the “Series A Preferred Stock,” “Series A-1 Preferred Stock,” and “Series B-1 Preferred Stock”, which are referred to collectively with the series B-2 convertible preferred stock (the “Series B-2 Preferred Stock”) and the series C convertible preferred stock (the “Series C Preferred Stock”) as the “Preferred Stock”) financings represented a freestanding financial instrument (the “Preferred Stock Tranche Obligation”). The freestanding financial instrument was classified as a liability on the Company’s condensed consolidated balance sheets and initially recorded at fair value, with changes in fair value for each reporting period recognized in other expense, net in the condensed consolidated statement of operations. The Board determined it was probable that the milestone would be met, and then the stockholders and the Board subsequently waived the Series B-2 Preferred Stock milestone and the issuance of the Series B-2 Preferred Stock on March 2, 2020. Instead of issuing the Series B-2 Preferred Stock upon this waiver, the Company instead closed its convertible Series C Preferred Stock financing (“Series C financing”). The associated Preferred Stock Tranche Obligation was remeasured prior to settlement, with the associated $1.5 million increase in fair value recorded in the Company’s condensed consolidated statement of operations as other expense, net. As the Series C financing was executed with related parties, the Company recognized the settlement of the Preferred Stock Tranche Obligation of $6.4 million as a capital contribution in additional paid-in capital in the Company’s condensed consolidated balance sheets. The following reflects the significant quantitative inputs used in the valuation of the Preferred Stock Tranche Obligation: MARCH 2, 2020 DECEMBER 31, 2019 Stand-alone Series B-1 Preferred Stock price (spot price) $ 7.28 $ 7.28 Estimated future value of Series B-2 Preferred Stock $ 8.14 $ 8.14 Discount rate 15.50 % 15.50 % Time to liquidity (years) 0.00 0.16 Probability of tranche closing 100 % 80 % The purchase price of the Preferred Stock at initial issuance, and all subsequent issuances was higher than the fair value of the Company’s common stock. The following table sets forth a summary of changes in the fair value and settlement of the Company’s Preferred Stock Tranche Obligation for which fair value was determined by Level 3 inputs (in thousands): PREFERRED STOCK TRANCHE OBLIGATION Balance as of January 1, 2019 $ 2,392 Change in fair value 2,564 Balance as of December 31, 2019 4,956 Change in fair value 1,490 Settlement of Preferred Stock Tranche Obligation (6,446) Balance as of September 30, 2020 $ — Fluctuations in the fair value of the Company’s Preferred Stock is the primary cause for the significant changes in fair value of the Preferred Stock Tranche Obligation. In 2020 and 2019, the enterprise value of the Company was determined using the Market Approach, specifically the Subject Company Transaction Method, which considers all share class rights and preferences, as of the date of the most recent financing. As part of the Company’s strategy, during 2019, the Company began considering the pursuit of longer-term liquidity options including a potential initial public offering, which caused an increase in the value of the Series B-1 Preferred Stock while reducing the value of the Preferred Stock Tranche Obligation.

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	9 Months Ended
	Sep. 30, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid Expenses and Other Current Assets	PREPAID EXPENSES AND OTHER CURRENT ASSETS Prepaid expenses and other current assets consisted of the following (in thousands): SEPTEMBER 30, DECEMBER 31, Prepaid service contracts $ 481 $ 21 Income tax credit receivable 172 — Prepaid sales tax 280 65 Prepaid rent — 64 Prepaid Insurance 1,543 16 Other 130 215 Total prepaid expenses and other current assets $ 2,606 $ 381

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	9 Months Ended
	Sep. 30, 2020
Payables and Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES Accrued expenses and other current liabilities consisted of the following (in thousands): SEPTEMBER 30, DECEMBER 31, Accrued external R&D costs $ 138 $ 645 Accrued external manufacturing costs 2,704 282 Accrued compensation and benefits 1,209 749 Accrued tax — 43 Accrued professional fees 206 34 Other 440 269 Total accrued expenses and other current liabilities $ 4,697 $ 2,022

Convertible Preferred Stock

Convertible Preferred Stock	9 Months Ended
	Sep. 30, 2020
Temporary Equity Disclosure [Abstract]
Convertible Preferred Stock	CONVERTIBLE PREFERRED STOCK On March 2, 2020, the Company authorized the sale and issuance of up to 9,049,783 shares of Series C Preferred Stock, par value $0.0001 per share, of which 4,169,822 shares were sold at a purchase price of $13.43 per share for gross proceeds of $56.0 million. Issuance costs were approximately $0.2 million. As part of the Company's Series C Preferred Stock issuance, 3,078,968 of the shares were issued to affiliates of members of the Board including entities affiliated with OrbiMed, entities affiliated with Pontifax, Arkin Bio Ventures Limited Partnership, entities affiliated with Partners Innovation Fund and Jasbir Seehra, Ph.D. All issued shares reflect the reverse stock split effected March 31, 2020 while the Board authorized shares reflect the original number of shares authorized pre-split. On April 13, 2020, upon the closing of the Company's IPO, all outstanding shares of Preferred Stock converted into 10,725,129 shares of the Company's common stock. Additionally, effective April 13, 2020, the Company's amended and restated certificate of incorporation authorized the issuance of 10,000,000 shares of preferred stock. There were no outstanding shares of Preferred Stock as of September 30, 2020. As of December 31, 2019, Preferred Stock consisted of the following (in thousands, except share data): PREFERRED PREFERRED STOCK ISSUED AND OUTSTANDING CARRYING LIQUIDATION COMMON STOCK ISSUABLE UPON CONVERSION Series A Preferred Stock 10,000,000 4,607,652 $ 9,891 $ 12,271 4,607,652 Series A-1 Preferred Stock 800,000 368,612 944 1,171 368,612 Series B-1 Preferred Stock 3,427,004 1,579,043 9,106 12,596 1,579,043 Series B-2 Preferred Stock 3,062,891 — — — — 17,289,895 6,555,307 $ 19,941 $ 26,038 6,555,307 The rights and privileges of the Preferred Stockholders were as follows: Conversion: Shares of Preferred Stock were convertible, at the option of the holder, at any time, into shares of common stock. The number of shares was determined by dividing the original issuance price by the conversion price. As such, the shares of Preferred Stock effectively converted on a one-for-one basis. The Preferred Stock would automatically convert to common stock at the closing of an IPO. No fractional shares would be issued. Liquidation Preference: Prior to the closing of the IPO, although the Preferred Stock was not redeemable, the shares were redeemable for cash in certain change of control events that are beyond the control of the Company. In the event of any liquidation or Deemed Liquidation Event (as defined in the Company’s articles of incorporation), the Preferred Stockholders would have been entitled to the greater of (i) the original issue price of the Preferred Stock plus any accrued dividends not yet paid plus any other dividends declared and unpaid or ii) the amount payable had all classes of shares been converted to common stock. In the event of a Deemed Liquidation Event, if the assets of the Company available for distribution were insufficient to pay the Preferred Stockholders in the full amount to which they were entitled, the Preferred Stockholders would have shared ratably in any distribution of the assets available for distribution in proportion to the number of shares of Preferred Stock that they held. Note that in relation to the above, the holders of Series C Preferred Stock were entitled to be paid out prior to the holders of common stock, Series A Preferred Stock, Series A-1 Preferred Stock and Series B-1 Preferred Stock. Dividends: Dividends accrued at a rate of $0.17, $0.22, $0.58263 and $1.07439 per share, per year on the anniversary of the issuance date for Series A Preferred Stock, Series A-1 Preferred Stock, Series B-1 Preferred Stock and Series C Preferred Stock, respectively. Dividends were cumulative; however, accrued dividends would be payable only if and when declared by the Board. Dividends on other classes of the Company’s stock were not to be declared or paid unless the Preferred Stockholders were first paid (i) all dividends accrued and not yet paid plus (ii) the product of (a) dividends declared on an as converted basis and (b) Preferred Stock on an as converted basis. That is, if the Company declared dividends on outstanding common stock, Preferred Stockholders would have received both the dividends owed for the Preferred Stock plus that which would be owed if the Preferred Stock were converted to common stock. No dividends were declared or paid through September 30, 2020.

Common Stock

Common Stock	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Common Stock	COMMON STOCK As of September 30, 2020, the Company’s amended and restated certificate of incorporation authorized the Company to issue 200,000,000 shares of common stock at a par value of $0.0001 per share. In conjunction with the Company's April 2020 IPO closing, the Company issued and sold 6,900,000 shares of its common stock, including 900,000 shares pursuant to the full exercise of the underwriters' option to purchase additional shares, at a public offering price of $16.00 per share, for aggregate net proceeds of $100.1 million after deducting underwriting discounts and commissions and offering costs. In connection with the IPO, all outstanding shares of Preferred Stock converted into 10,725,129 shares of common stock. The following is a summary of the rights and privileges of the holders of common stock as of September 30, 2020: Liquidation Preference: In the event of liquidation, dissolution or winding up, holders of common stock will be entitled to share ratably in the net assets legally available for distribution to stockholders after the payment of all debts and other liabilities and the satisfaction of any liquidation preference granted to the holders of any then-outstanding shares of preferred stock. Dividends: Subject to preferences that may be applicable to any then-outstanding preferred stock, holders of common stock are entitled to receive ratably those dividends, if any, as may be declared from time to time by the Board out of legally available funds. As of September 30, 2020, no cash dividends have been declared or paid. Voting Rights: Each holder of common stock is entitled to one vote for each share on all matters submitted to a vote of the stockholders, including the election of directors. Under the Company's amended and restated certificate of incorporation and amended and restated bylaws, stockholders will not have cumulative voting rights. Because of this, the holders of a majority of the shares of common stock entitled to vote in any election of directors can elect all of the directors standing for election, if they should so choose. Rights and Preferences : Holders of common stock have no preemptive, conversion or subscription rights and there are no redemption or sinking fund provisions applicable to the common stock. The rights, preferences and privileges of the holders of common stock are subject to, and may be adversely affected by, the rights of the holders of shares of any series of preferred stock that the Company may designate in the future. As of September 30, 2020 and December 31, 2019, the Company has reserved the following shares of common stock for potential conversion of outstanding Preferred Stock, the vesting of restricted stock and exercise of stock options: SEPTEMBER 30, DECEMBER 31, Preferred Stock — 6,555,307 Unvested restricted stock — 34,557 Options to purchase common stock 2,484,152 1,164,017 Total 2,484,152 7,753,881

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2020
Share-based Payment Arrangement [Abstract]
Stock-Based Compensation	STOCK-BASED COMPENSATION 2017 Stock Incentive Plan The Board adopted the 2017 Stock Incentive Plan (the "2017 Plan") in February 2017, and the stockholders approved the 2017 Plan in March 2017. The 2017 Plan was most recently amended in March 2020. As of September 30, 2020, there were an aggregate of 1,064,648 shares of common stock issuable upon the exercise of outstanding options under the 2017 Plan. Any options or awards outstanding under the 2017 Plan remain outstanding and effective. 2020 Equity Incentive Plan In April 2020, the 2020 Equity Incentive Plan (the "2020 Plan") became effective, and, as a result, no further awards will be made under the 2017 Plan. The 2020 Plan provides for the grant of stock options qualifying as incentive stock options ("ISOs"), to employees and for the grant of nonstatutory stock options ("NSOs"), restricted stock awards, restricted stock unit awards, stock appreciation rights, performance stock awards and other forms of stock compensation to employees, consultants and directors. The 2020 Plan also provides for the grant of performance cash awards to employees, consultants and directors. Any previously granted awards under the 2017 Plan will remain outstanding in accordance with their respective terms. In March 2020, the Board approved an aggregate of 1,991,530 options under the 2020 Plan. No shares of common stock have been issued under the 2020 Plan. As of September 30, 2020, the number of shares of common stock reserved for issuance under the 2020 Plan was 1,991,530. The number of shares of common stock initially reserved for issuance under the 2020 Plan is the sum of (i) 1,002,874 new shares of common stock, plus (ii) an additional number of shares not to exceed 2,104,937 shares, consisting of (A) the number of shares remaining available for issuance under the 2017 Plan when the 2020 Plan became effective and (B) the number of shares of common stock subject to outstanding awards under the 2017 Plan when the 2020 Plan became effective that thereafter expire or are forfeited, canceled, withheld to satisfy tax withholding or to purchase or exercise an award, reacquired by the Company or are otherwise terminated. The number of shares of common stock reserved for issuance under the 2020 Plan will automatically increase on January 1 of each year, for a period of ten years, from January 1, 2021 continuing through January 1, 2030, by 4.0% of the total number of shares of common stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares as may be determined by the Board. As of September 30, 2020, there were an aggregate of 1,419,504 shares of common stock issuable upon the exercise of outstanding options under the 2020 Plan. Additionally, there were an aggregate of 572,026 shares reserved for future issuance under the 2020 Plan. Stock Options A summary of option activity during the nine months ended September 30, 2020 is as follows (in thousands except share and per share data): NUMBER OF OPTIONS WEIGHTED-AVERAGE EXERCISE PRICE WEIGHTED-AVERAGE REMAINING CONTRACTUAL TERM (IN YEARS) AGGREGATE INTRINSIC VALUE Outstanding as of December 31, 2019 1,164,017 $ 0.35 8.64 $ 144 Granted 1,419,504 18.90 Exercised (96,339) 0.33 $ 2,173 Expired (3,030) 0.16 Outstanding as of September 30, 2020 2,484,152 $ 10.95 8.85 $ 68,959 Options exercisable as of December 31, 2019 608,156 $ 0.29 8.17 $ 112 Options exercisable as of September 30, 2020 694,023 $ 0.49 7.61 $ 26,436 As of September 30, 2020 and 2019, respectively, there was $18.5 million and $0.2 million of unrecognized stock-based compensation expense related to unvested stock options, which is being recognized over a period of 3.23 years as of September 30, 2020. Shares of Restricted Common Stock The Company has granted shares of restricted common stock with time-based vesting conditions. A summary of restricted stock activity during the nine months ended September 30, 2020 is as follows: NINE MONTHS ENDED SEPTEMBER 30, 2020 Unvested at the beginning of the period 34,557 Vested or released (34,557) Unvested at the end of the period — During the nine months ended September 30, 2020 and 2019, respectively, there was $0 and less than $1,000 of unrecognized stock-based compensation expense related to unvested restricted stock. There is no unvested restricted stock as of September 30, 2020. Stock-Based Compensation Expense Total stock-based compensation expense recorded for employees, directors and non-employees during the nine months ended September 30, 2020 and 2019 was as follows (in thousands): THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, 2020 2019 2020 2019 Research and development $ 465 $ 8 $ 786 $ 21 General and administrative 959 9 1,789 20 Total stock-based compensation expense $ 1,424 $ 17 $ 2,575 $ 41

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXESOn March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act (“CARES Act”) was signed into law in the United States. The CARES Act provides numerous tax provisions and other stimulus measures, including temporary changes regarding the prior and future utilization of net operating losses and technical corrections from prior tax legislation for tax depreciation of certain qualified improvement property. The Company evaluated the provisions of the CARES Act and as a result recorded an income tax receivable of approximately $0.2 million related to the potential carryback of our 2019 net operating loss to claim a refund for prior federal tax liabilities.

Loss Per Share

Loss Per Share	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Loss Per Share	LOSS PER SHARE Basic and diluted loss per share is computed by dividing net loss attributable to common stockholders by the weighted-average common shares outstanding (in thousands, except share and per share data): THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, 2020 2019 2020 2019 Numerator: Net loss $ (12,036) $ (3,549) $ (34,685) $ (9,585) Less: Accruals of dividends of preferred stock 0 (450) (1,012) (1,350) Net loss attributable to common stockholders - basic and diluted $ (12,036) $ (3,999) $ (35,697) $ (10,935) Denominator: Weighted-average common stock outstanding - basic and diluted 20,175,883 2,342,782 13,452,606 2,296,701 Net loss per share attributable to common stockholders - basic and diluted $ (0.60) $ (1.71) $ (2.65) $ (4.76) The Company’s potentially dilutive securities, which include Preferred Stock, restricted stock, and stock options, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted-average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company excluded the following from the computation of diluted net loss per share attributable to common stockholders at September 30, 2020 and 2019 because including them would have had an anti-dilutive effect: SEPTEMBER 30, SEPTEMBER 30, Preferred Stock — 6,555,307 Unvested restricted stock — 60,474 Options to purchase common stock 2,484,152 1,209,272 2,484,152 7,825,053

Revenue from Contracts with Cus

Revenue from Contracts with Customers	9 Months Ended
	Sep. 30, 2020
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	REVENUE FROM CONTRACTS WITH CUSTOMERS The Company adopted FASB Accounting Standards Codification Subtopic 606, Revenue from Contracts with Customers ("ASC 606") on January 1, 2018 applying the full retrospective method to all contracts that were not completed as of January 1, 2018. While the timing of future revenue under ASC 606 may differ from the Company’s historical accounting practices under FASB Accounting Standards Codification Subtopic 605, Revenue Recognition ("ASC 605"), the cumulative effect recognized in the condensed consolidated statement of stockholder’s deficit was $0 because there was no change in timing or measurement of revenue for open contracts at January 1, 2018. Novo Nordisk Agreement Background On December 14, 2017, the Company entered into a research collaboration and exclusive license agreement with Novo Nordisk A/S (“Novo,” agreement referred to as the “Novo Agreement”). The Novo Agreement stipulates that the two parties will work together on the discovery and development of new ligand traps for two years. Under the Novo Agreement, Keros granted Novo an exclusive license to develop and commercialize the licensed products listed as part of Keros’ intellectual property and Novo granted Keros a non-exclusive license to Novo’s intellectual property so that Keros could perform the activities for which it is responsible under the Novo Agreement. The Company does not share in the rights to the results of the Novo Agreement. On October 26, 2020, Novo provided the Company with written notice of termination of the Novo Agreement, effective April 26, 2021. Upon the termination of the Novo Agreement, the license granted by the Company to Novo will be automatically terminated. Accordingly, the Company's singular performance obligation will be fully satisfied upon termination. Novo Nordisk is obligated to continue to reimburse the Company for certain research and development costs through April 26, 2021. Upon effectiveness of the termination, such reimbursements will cease. Accounting Treatment As consideration, the Company received an initial license payment in 2018 from Novo in the amount of $16.0 million. Novo has also paid the Company research collaboration budget funding payments of $2.0 million per each collaboration year, for $4.0 million total. Both of these research collaboration budget funding payments were received in 2018. Additionally, there are performance-based and sales-based milestone payments and sales-based royalties that have been determined to be variable consideration and constrained due to uncertainty of achievement. The sales-based royalties will be included in the transaction price and recognized as revenue once a sale occurs, and performance-based and sales-based milestone payments will be included in the transaction price and recognized as revenue if and when the cumulative revenue associated with the consideration is no longer probable of significant reversal. The Company assessed this arrangement in accordance with ASC 606 and concluded that the contract counterparty, Novo, is a customer. The Company identified the following material promises at the outset of the Novo Agreement: (1) an exclusive license to use the Company’s intellectual property to conduct research activities; (2) research and development (“R&D”) services for activities under the research plan; (3) an option to extend the Novo Agreement; (4) participation on the joint steering committee (“JSC”); and (5) technology transfer associated with the research and development outputs. The Company determined that these promises were not capable of being distinct from one another and were not distinct in the context of the contract, as the license has no true value without the performance of the R&D activities and the technology transfer and JSC participation depend on these activities. Novo would not be able to use the license without the performance of R&D activities by the Company, as the research is novel in nature and could not be performed by another company. Additionally, the technology transfer is inherently dependent on the outcome of the Company’s R&D activities, and as such is not capable of being distinct. As indicated in number (3) above, Novo may elect to extend the term of the Novo Agreement to a third year on similar terms and conditions, subject to mutual written agreement of Novo and the Company. The Company assessed this option as a potential material right and determined that the additional work would be performed based on negotiated rates at the standalone selling price, and as such these services would not be provided at a significant or incremental discount and the option does not provide Novo with a material right. In accordance with the Company’s ASC 606 assessment, the Novo Agreement was determined to contain a single combined performance obligation made up of the promises above, which does not require further allocation as the entire transaction price is allocated to this performance obligation. The Company determined the contract term of the Novo Agreement to be two years. The Company identified an appropriate measure of progress for the recognition of revenue and determined it would recognize the revenue over the term of the Novo Agreement using an input method based on full-time employee costs incurred, as this appropriately depicts the Company’s performance in satisfaction of the performance obligation. As such, the Company is recognizing the transaction price for its single performance obligation as Novo uses the license and research and development services performed by the Company and as the Company participates on the JSC.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Basis of Accounting	The accompanying unaudited interim condensed consolidated financial statements are prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and include the accounts of the Company and its wholly owned Australian subsidiary, Keros Therapeutics Australia Pty Ltd (“Keros Australia”). All significant intercompany transactions and accounts have been eliminated in consolidation.
Deferred Offering Costs	Deferred Offering CostsThe Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ deficit as a reduction of proceeds generated as a result of the offering. Should a planned equity financing be abandoned, the deferred offering costs would be expensed immediately as a charge to operating expenses in the condensed consolidated statement of operations.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements The new accounting pronouncements recently adopted by the Company and issued by the Financial Accounting Standards Board ("FASB") that are applicable to the Company are described in the Company’s audited financial statements as of and for the year ended December 31, 2019, and the notes thereto, which are included in the Company’s Prospectus filed with the SEC on April 8, 2020. There have been no new accounting pronouncements issued in the nine months ended September 30, 2020 that are applicable to the Company.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	The following table presents information about the Company’s financial assets and liabilities measured at fair value on a recurring basis and indicates the level of the fair value hierarchy utilized to determine such fair values (in thousands): DESCRIPTION SEPTEMBER 30, 2020 QUOTED PRICES ACTIVE MARKETS FOR IDENTICAL ASSETS SIGNIFICANT OTHER OBSERVABLE INPUTS SIGNIFICANT OTHER OBSERVABLE INPUTS Asset Money market funds $ 128,668 $ 128,668 $ — $ — Total financial assets $ 128,668 $ 128,668 $ — $ — DESCRIPTION DECEMBER 31, 2019 QUOTED PRICES ACTIVE MARKETS FOR IDENTICAL ASSETS (LEVEL 1) SIGNIFICANT OTHER OBSERVABLE INPUTS (LEVEL 2) SIGNIFICANT OTHER OBSERVABLE INPUTS (LEVEL 3) Asset Money market funds $ 4,972 $ 4,972 $ — $ — Total financial assets $ 4,972 $ 4,972 $ — $ — Liability Preferred stock tranche obligation $ (4,956) $ — $ — $ (4,956) Total financial liabilities $ (4,956) $ — $ — $ (4,956)
Fair Value Measurement Inputs and Valuation Techniques	The following reflects the significant quantitative inputs used in the valuation of the Preferred Stock Tranche Obligation: MARCH 2, 2020 DECEMBER 31, 2019 Stand-alone Series B-1 Preferred Stock price (spot price) $ 7.28 $ 7.28 Estimated future value of Series B-2 Preferred Stock $ 8.14 $ 8.14 Discount rate 15.50 % 15.50 % Time to liquidity (years) 0.00 0.16 Probability of tranche closing 100 % 80 %
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation	The following table sets forth a summary of changes in the fair value and settlement of the Company’s Preferred Stock Tranche Obligation for which fair value was determined by Level 3 inputs (in thousands): PREFERRED STOCK TRANCHE OBLIGATION Balance as of January 1, 2019 $ 2,392 Change in fair value 2,564 Balance as of December 31, 2019 4,956 Change in fair value 1,490 Settlement of Preferred Stock Tranche Obligation (6,446) Balance as of September 30, 2020 $ —

Prepaid Expenses and Other Cu_2

Prepaid Expenses and Other Current Assets (Tables)	9 Months Ended
	Sep. 30, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Summary of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following (in thousands): SEPTEMBER 30, DECEMBER 31, Prepaid service contracts $ 481 $ 21 Income tax credit receivable 172 — Prepaid sales tax 280 65 Prepaid rent — 64 Prepaid Insurance 1,543 16 Other 130 215 Total prepaid expenses and other current assets $ 2,606 $ 381

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	9 Months Ended
	Sep. 30, 2020
Payables and Accruals [Abstract]
Summary of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): SEPTEMBER 30, DECEMBER 31, Accrued external R&D costs $ 138 $ 645 Accrued external manufacturing costs 2,704 282 Accrued compensation and benefits 1,209 749 Accrued tax — 43 Accrued professional fees 206 34 Other 440 269 Total accrued expenses and other current liabilities $ 4,697 $ 2,022

Convertible Preferred Stock (Ta

Convertible Preferred Stock (Tables)	9 Months Ended
	Sep. 30, 2020
Temporary Equity Disclosure [Abstract]
Summary of Preferred Stock	As of December 31, 2019, Preferred Stock consisted of the following (in thousands, except share data): PREFERRED PREFERRED STOCK ISSUED AND OUTSTANDING CARRYING LIQUIDATION COMMON STOCK ISSUABLE UPON CONVERSION Series A Preferred Stock 10,000,000 4,607,652 $ 9,891 $ 12,271 4,607,652 Series A-1 Preferred Stock 800,000 368,612 944 1,171 368,612 Series B-1 Preferred Stock 3,427,004 1,579,043 9,106 12,596 1,579,043 Series B-2 Preferred Stock 3,062,891 — — — — 17,289,895 6,555,307 $ 19,941 $ 26,038 6,555,307 As of September 30, 2020 and December 31, 2019, the Company has reserved the following shares of common stock for potential conversion of outstanding Preferred Stock, the vesting of restricted stock and exercise of stock options: SEPTEMBER 30, DECEMBER 31, Preferred Stock — 6,555,307 Unvested restricted stock — 34,557 Options to purchase common stock 2,484,152 1,164,017 Total 2,484,152 7,753,881

Common Stock (Tables)

Common Stock (Tables)	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Summary of Common Stock Reserved for Potential Conversion of Outstanding Preferred Stock and Vesting of Restricted Stock and Exercise of Stock Options	As of December 31, 2019, Preferred Stock consisted of the following (in thousands, except share data): PREFERRED PREFERRED STOCK ISSUED AND OUTSTANDING CARRYING LIQUIDATION COMMON STOCK ISSUABLE UPON CONVERSION Series A Preferred Stock 10,000,000 4,607,652 $ 9,891 $ 12,271 4,607,652 Series A-1 Preferred Stock 800,000 368,612 944 1,171 368,612 Series B-1 Preferred Stock 3,427,004 1,579,043 9,106 12,596 1,579,043 Series B-2 Preferred Stock 3,062,891 — — — — 17,289,895 6,555,307 $ 19,941 $ 26,038 6,555,307 As of September 30, 2020 and December 31, 2019, the Company has reserved the following shares of common stock for potential conversion of outstanding Preferred Stock, the vesting of restricted stock and exercise of stock options: SEPTEMBER 30, DECEMBER 31, Preferred Stock — 6,555,307 Unvested restricted stock — 34,557 Options to purchase common stock 2,484,152 1,164,017 Total 2,484,152 7,753,881

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2020
Share-based Payment Arrangement [Abstract]
Summary of Option Activity	A summary of option activity during the nine months ended September 30, 2020 is as follows (in thousands except share and per share data): NUMBER OF OPTIONS WEIGHTED-AVERAGE EXERCISE PRICE WEIGHTED-AVERAGE REMAINING CONTRACTUAL TERM (IN YEARS) AGGREGATE INTRINSIC VALUE Outstanding as of December 31, 2019 1,164,017 $ 0.35 8.64 $ 144 Granted 1,419,504 18.90 Exercised (96,339) 0.33 $ 2,173 Expired (3,030) 0.16 Outstanding as of September 30, 2020 2,484,152 $ 10.95 8.85 $ 68,959 Options exercisable as of December 31, 2019 608,156 $ 0.29 8.17 $ 112 Options exercisable as of September 30, 2020 694,023 $ 0.49 7.61 $ 26,436
Summary of Restricted Stock Activity	A summary of restricted stock activity during the nine months ended September 30, 2020 is as follows: NINE MONTHS ENDED SEPTEMBER 30, 2020 Unvested at the beginning of the period 34,557 Vested or released (34,557) Unvested at the end of the period —
Schedule of Stock-based Compensation Expense	Total stock-based compensation expense recorded for employees, directors and non-employees during the nine months ended September 30, 2020 and 2019 was as follows (in thousands): THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, 2020 2019 2020 2019 Research and development $ 465 $ 8 $ 786 $ 21 General and administrative 959 9 1,789 20 Total stock-based compensation expense $ 1,424 $ 17 $ 2,575 $ 41

Loss Per Share (Tables)

Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Basic and Diluted Loss Per Share Calculation	Basic and diluted loss per share is computed by dividing net loss attributable to common stockholders by the weighted-average common shares outstanding (in thousands, except share and per share data): THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, 2020 2019 2020 2019 Numerator: Net loss $ (12,036) $ (3,549) $ (34,685) $ (9,585) Less: Accruals of dividends of preferred stock 0 (450) (1,012) (1,350) Net loss attributable to common stockholders - basic and diluted $ (12,036) $ (3,999) $ (35,697) $ (10,935) Denominator: Weighted-average common stock outstanding - basic and diluted 20,175,883 2,342,782 13,452,606 2,296,701 Net loss per share attributable to common stockholders - basic and diluted $ (0.60) $ (1.71) $ (2.65) $ (4.76)
Schedule of Antidilutive Securities Excluded From Computation of Diluted Net Loss Per Share	The Company excluded the following from the computation of diluted net loss per share attributable to common stockholders at September 30, 2020 and 2019 because including them would have had an anti-dilutive effect: SEPTEMBER 30, SEPTEMBER 30, Preferred Stock — 6,555,307 Unvested restricted stock — 60,474 Options to purchase common stock 2,484,152 1,209,272 2,484,152 7,825,053

Nature of Business and Basis _2

Nature of Business and Basis of Presentation (Details) - USD ($) $ / shares in Units, $ in Thousands	Apr. 13, 2020	Jun. 30, 2020	Sep. 30, 2020	Sep. 30, 2019
Class of Stock [Line Items]
Issuance of initial public offering	$ 110,400		$ 102,672	$ 0
Proceeds from initial public offering, net of discounts and offering costs	$ 100,100
Common Stock
Class of Stock [Line Items]
Conversion of convertible preferred stock upon initial public offering (in shares)	10,725,129	10,725,129
IPO
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	6,900,000
Sale of stock, price per share (USD per share)	$ 16
Over-Allotment Option
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	900,000

Summary of Significant Accoun_3

Summary of Significant Accounting Polices (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Deferred offering costs	$ 0	$ 604

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Liability
Preferred stock tranche obligation	$ 0	$ (4,956)
Fair Value, Recurring
Asset
Money market funds	128,668	4,972
Total financial assets	128,668	4,972
Liability
Preferred stock tranche obligation		(4,956)
Total financial liabilities		(4,956)
Fair Value, Recurring | QUOTED PRICES ACTIVE MARKETS FOR IDENTICAL ASSETS (LEVEL 1)
Asset
Money market funds	128,668	4,972
Total financial assets	128,668	4,972
Liability
Preferred stock tranche obligation		0
Total financial liabilities		0
Fair Value, Recurring | SIGNIFICANT OTHER OBSERVABLE INPUTS (LEVEL 2)
Asset
Money market funds	0	0
Total financial assets	0	0
Liability
Preferred stock tranche obligation		0
Total financial liabilities		0
Fair Value, Recurring | SIGNIFICANT OTHER OBSERVABLE INPUTS (LEVEL 3)
Asset
Money market funds	0	0
Total financial assets	$ 0	0
Liability
Preferred stock tranche obligation		(4,956)
Total financial liabilities		$ (4,956)

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in fair value of preferred stock tranche obligation	$ 0	$ 1,235,000	$ 1,490,000	$ 2,486,000
Preferred Stock Tranche Obligation
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in fair value of preferred stock tranche obligation			1,490,000		$ 2,564,000
Settlement of Preferred Stock Tranche Obligation			6,446,000
Preferred stock tranche obligation	$ 0		$ 0		$ 4,956,000	$ 2,392,000

Fair Value Measurements - Signi

Fair Value Measurements - Significant Quantitative Inputs (Details)	Mar. 02, 2020$ / shares	Dec. 31, 2019$ / shares
Stand-alone Series B-1 Preferred Stock price (spot price) | Series B-1 Preferred Stock
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Preferred stock tranche obligation, measurement input (USD per share)	$ 7.28	$ 7.28
Estimated future value of Series B-2 Preferred Stock | Series B-2 Preferred Stock
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Preferred stock tranche obligation, measurement input (USD per share)	$ 8.14	$ 8.14
Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Preferred stock tranche obligation, measurement input, percent	0.1550	0.1550
Time to liquidity (years)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Preferred stock tranche obligation, measurement input, term	0 years	1 month 28 days
Probability of tranche closing
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Preferred stock tranche obligation, measurement input, percent	1	0.80

Fair Value Measurements - Chang

Fair Value Measurements - Changes in Level 3 Fair Value Liabilities (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Change in fair value	$ 0	$ 1,235,000	$ 1,490,000	$ 2,486,000
Preferred Stock Tranche Obligation
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance			4,956,000	$ 2,392,000	$ 2,392,000
Change in fair value			1,490,000		2,564,000
Settlement of Preferred Stock Tranche Obligation			(6,446,000)
Ending balance	$ 0		$ 0		$ 4,956,000

Prepaid Expenses and Other Cu_3

Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid service contracts	$ 481	$ 21
Income tax credit receivable	172	0
Prepaid sales tax	280	65
Prepaid rent	0	64
Prepaid Insurance	1,543	16
Other	130	215
Prepaid expenses and other current assets	$ 2,606	$ 381

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Accrued external R&D costs	$ 138	$ 645
Accrued external manufacturing costs	2,704	282
Accrued compensation and benefits	1,209	749
Accrued tax	0	43
Accrued professional fees	206	34
Other	440	269
Total accrued expenses and other current liabilities	$ 4,697	$ 2,022

Convertible Preferred Stock - N

Convertible Preferred Stock - Narrative (Details) - USD ($)	Mar. 02, 2020	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Apr. 13, 2020	Dec. 31, 2019
Temporary Equity [Line Items]
Shares authorized (in shares)						17,289,895
Issuance costs		$ 219,000	$ 227,000	$ 0
Common stock issuable upon conversion (in shares)						6,555,307
Shares authorized, preferred stock (in shares)					10,000,000
Shares outstanding, preferred stock (in shares)			0
Convertible preferred stock, conversion ratio (in shares)			1
Series C preferred stock
Temporary Equity [Line Items]
Shares authorized (in shares)	9,049,783
Par value (USD per share)	$ 0.0001		$ 0.0001	$ 0.0001
Sale of stock, number of shares issued in transaction (in shares)	4,169,822
Sale of stock, price per share (USD per share)	$ 13.43
Gross proceeds from issuance of convertible preferred stock	$ 56,000,000
Issuance costs	$ 200,000
Preferred stock, dividend rate (USD per share)			$ 1.07439
Series C preferred stock | Affiliates of the Board
Temporary Equity [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	3,078,968
Common Stock
Temporary Equity [Line Items]
Common stock issuable upon conversion (in shares)					10,725,129
Common Stock | Dividend Declared
Temporary Equity [Line Items]
Dividends payable			$ 0
Series A Preferred Stock
Temporary Equity [Line Items]
Shares authorized (in shares)			0			10,000,000
Par value (USD per share)			$ 0.0001	0.0001		$ 0.0001
Common stock issuable upon conversion (in shares)						4,607,652
Preferred stock, dividend rate (USD per share)			$ 0.17
Series A-1 Preferred Stock
Temporary Equity [Line Items]
Shares authorized (in shares)			0			800,000
Par value (USD per share)			$ 0.0001	0.0001		$ 0.0001
Common stock issuable upon conversion (in shares)						368,612
Preferred stock, dividend rate (USD per share)			$ 0.22
Series B-1 Preferred Stock
Temporary Equity [Line Items]
Shares authorized (in shares)			0			3,427,004
Par value (USD per share)			$ 0.0001	$ 0.0001		$ 0.0001
Common stock issuable upon conversion (in shares)						1,579,043
Preferred stock, dividend rate (USD per share)			$ 0.58263
Convertible Preferred Stock | Dividend Declared
Temporary Equity [Line Items]
Dividends payable			$ 0

Convertible Preferred Stock - S

Convertible Preferred Stock - Summary of Preferred Stock (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Temporary Equity [Line Items]
PREFERRED STOCK AUTHORIZED (in shares)				17,289,895
PREFERRED STOCK ISSUED (in shares)				6,555,307
PREFERRED STOCK OUTSTANDING (in shares)				6,555,307
CARRYING VALUE				$ 19,941
LIQUIDATION VALUE				$ 26,038
COMMON STOCK ISSUABLE UPON CONVERSION (in shares)				6,555,307
Series A Preferred Stock
Temporary Equity [Line Items]
PREFERRED STOCK AUTHORIZED (in shares)	0			10,000,000
PREFERRED STOCK ISSUED (in shares)	0			4,607,652
PREFERRED STOCK OUTSTANDING (in shares)	0	0	4,607,652	4,607,652	4,607,652	4,607,652	4,607,652	4,607,652
CARRYING VALUE	$ 0	$ 0	$ 9,891	$ 9,891	$ 9,891	$ 9,891	$ 9,891	$ 9,891
LIQUIDATION VALUE	$ 0			$ 12,271
COMMON STOCK ISSUABLE UPON CONVERSION (in shares)				4,607,652
Series A-1 Preferred Stock
Temporary Equity [Line Items]
PREFERRED STOCK AUTHORIZED (in shares)	0			800,000
PREFERRED STOCK ISSUED (in shares)	0			368,612
PREFERRED STOCK OUTSTANDING (in shares)	0	0	368,612	368,612	368,612	368,612	368,612	368,612
CARRYING VALUE	$ 0	$ 0	$ 944	$ 944	$ 944	$ 944	$ 944	$ 944
LIQUIDATION VALUE	$ 0			$ 1,171
COMMON STOCK ISSUABLE UPON CONVERSION (in shares)				368,612
Series B-1 Preferred Stock
Temporary Equity [Line Items]
PREFERRED STOCK AUTHORIZED (in shares)	0			3,427,004
PREFERRED STOCK ISSUED (in shares)	0			1,579,043
PREFERRED STOCK OUTSTANDING (in shares)	0	0	1,579,043	1,579,043	1,579,043	1,579,043	1,579,043	1,579,043
CARRYING VALUE	$ 0	$ 0	$ 9,106	$ 9,106	$ 9,106	$ 9,106	$ 9,106	$ 9,106
LIQUIDATION VALUE	$ 0			$ 12,596
COMMON STOCK ISSUABLE UPON CONVERSION (in shares)				1,579,043
Series B-2 Preferred Stock
Temporary Equity [Line Items]
PREFERRED STOCK AUTHORIZED (in shares)				3,062,891
PREFERRED STOCK ISSUED (in shares)				0
PREFERRED STOCK OUTSTANDING (in shares)				0
CARRYING VALUE				$ 0
LIQUIDATION VALUE				$ 0
COMMON STOCK ISSUABLE UPON CONVERSION (in shares)				0

Common Stock - Narrative (Detai

Common Stock - Narrative (Details)	Apr. 13, 2020USD ($)$ / sharesshares	Sep. 30, 2020USD ($)vote$ / sharesshares	Dec. 31, 2019$ / sharesshares	Sep. 30, 2019$ / shares
Class of Stock [Line Items]
Common stock, shares authorized (in shares)		200,000,000	27,000,000
Common stock, par value (USD per share) | $ / shares		$ 0.0001	$ 0.0001	$ 0.0001
Proceeds from initial public offering, net of discounts and offering costs | $	$ 100,100,000
Common stock issuable upon conversion (in shares)			6,555,307
Number of votes per common share held | vote		1
IPO
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	6,900,000
Sale of stock, price per share (USD per share) | $ / shares	$ 16
Over-Allotment Option
Class of Stock [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	900,000
Common Stock
Class of Stock [Line Items]
Common stock issuable upon conversion (in shares)	10,725,129
Dividend Declared | Common Stock
Class of Stock [Line Items]
Dividends payable | $		$ 0

Common Stock - Summary of Commo

Common Stock - Summary of Common Stock Reserved for Future Issuance (Details) - shares	Sep. 30, 2020	Dec. 31, 2019
Class of Stock [Line Items]
Common stock, reserved for future issuance (in shares)	2,484,152	7,753,881
Unvested restricted stock
Class of Stock [Line Items]
Common stock, reserved for future issuance (in shares)	0	34,557
Options to purchase common stock
Class of Stock [Line Items]
Common stock, reserved for future issuance (in shares)	2,484,152	1,164,017
Preferred Stock
Class of Stock [Line Items]
Common stock, reserved for future issuance (in shares)	0	6,555,307

Stock-Based Compensation - Narr

Stock-Based Compensation - Narrative (Details) - USD ($)	1 Months Ended	9 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, reserved for future issuance (in shares)		2,484,152	7,753,881
Granted (in shares)		1,419,504
Unrecognized stock-based compensation expense related to unvested stock options		$ 18,500,000		$ 200,000
Unrecognized stock-based compensation expense related to unvested restricted stock (less than)		$ 0		$ 1,000
Employee Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, reserved for future issuance (in shares)		2,484,152	1,164,017
Unvested award, period for recognition		3 years 2 months 23 days
2017 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)		1,064,648
2020 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)		1,991,530
Number of shares issued, common stock (in shares)		0
Common stock, reserved for future issuance (in shares)	1,002,874
Number of additional shares authorized (in shares)	2,104,937
Number of years of annual increases in shares authorized		10 years
Annual percentage increase in shares authorized		4.00%
Granted (in shares)		1,419,504
Number of shares available for future grants (in shares)		572,026

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020USD ($)$ / sharesshares	Dec. 31, 2019USD ($)$ / sharesshares
NUMBER OF OPTIONS
Outstanding as of beginning of period (in shares) | shares	1,164,017
Granted (in shares) | shares	1,419,504
Exercised (in shares) | shares	(96,339)
Expired (in shares) | shares	(3,030)
Outstanding as of end of period (in shares) | shares	2,484,152	1,164,017
Exercisable (in shares) | shares	694,023	608,156
WEIGHTED-AVERAGE EXERCISE PRICE
Outstanding as of beginning of period (USD per share) | $ / shares	$ 0.35
Granted (USD per share) | $ / shares	18.90
Exercised (USD per share) | $ / shares	0.33
Expired (USD per share) | $ / shares	0.16
Outstanding as of end of period (USD per share) | $ / shares	10.95	$ 0.35
Exercisable (USD per share) | $ / shares	$ 0.49	$ 0.29
WEIGHTED-AVERAGE REMAINING CONTRACTUAL TERM (IN YEARS)
Outstanding	8 years 10 months 6 days	8 years 7 months 20 days
Exercisable	7 years 7 months 9 days	8 years 2 months 1 day
AGGREGATE INTRINSIC VALUE
Outstanding | $	$ 68,959	$ 144
Exercised | $	2,173
Exercisable | $	$ 26,436	$ 112

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock Activity (Details) - Restricted Stock	9 Months Ended
	Sep. 30, 2020shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested at the beginning of the period (in shares)	34,557
Vested or released (in shares)	(34,557)
Unvested at the end of the period (in shares)	0

Stock-Based Compensation - St_2

Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 1,424	$ 17	$ 2,575	$ 41
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	465	8	786	21
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 959	$ 9	$ 1,789	$ 20

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income tax credit receivable	$ 172	$ 0

Loss Per Share - Calculation (D

Loss Per Share - Calculation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net loss	$ (12,036)	$ (10,757)	$ (11,892)	$ (3,549)	$ (2,853)	$ (3,183)	$ (34,685)	$ (9,585)
Less: Accruals of dividends of preferred stock	0			(450)			(1,012)	(1,350)
Net loss attributable to common stockholders - basic and diluted	$ (12,036)			$ (3,999)			$ (35,697)	$ (10,935)
Denominator:
Weighted-average common stock outstanding - basic and diluted (in shares)	20,175,883			2,342,782			13,452,606	2,296,701
Net loss per share attributable to common stockholders - basic and diluted (USD per share)	$ (0.60)			$ (1.71)			$ (2.65)	$ (4.76)

Loss Per Share - Antidilutive S

Loss Per Share - Antidilutive Securities (Details) - shares	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	2,484,152	7,825,053
Preferred Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	0	6,555,307
Unvested restricted stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	0	60,474
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	2,484,152	1,209,272

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Details) - USD ($)	Dec. 14, 2017	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2019	Jan. 01, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accumulated deficit		$ (54,335,000)		$ (54,335,000)			$ (19,650,000)
Research collaboration revenue		$ 0	$ 2,500,000	$ 0	$ 7,500,000
Deferred revenue							0
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accumulated deficit								$ 0
License Agreement | Novo Nordisk A/S
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
License agreement proceeds received						$ 16,000,000
Annual collaboration budget funding	$ 2,000,000
Cumulative proceeds received from collaboration budget funding							$ 4,000,000