89bio (ETNB) 10-K 18 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	Mar. 10, 2020	Mar. 02, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Registrant Name	89bio, Inc.
Entity Central Index Key	0001785173
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Well-known Seasoned Issuer	No
Entity Public Float			$ 169,328,521
Entity Common Stock, Shares Outstanding		13,788,982
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Title of 12(b) Security	Common stock, par value $0.001 per share
Trading Symbol	ETNB
Security Exchange Name	NASDAQ
Entity File Number	001-39122
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	36-4946844
Entity Address, Address Line One	142 Sansome Street
Entity Address Address Line Two	Second Floor
Entity Address, City or Town	San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94104
City Area Code	415
Local Phone Number	500-4614
Document Annual Report	true
Document Transition Report	false

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 93,335,000	$ 11,234,000
Restricted cash	25,000	23,000
Prepaid and other current assets	1,966,000	59,000
Total current assets	95,326,000	11,316,000
Property and equipment, net	155,000	33,000
Deferred tax assets		20,000
Other assets	72,000
Total assets	95,553,000	11,369,000
Current liabilities:
Accounts payable	989,000	1,509,000
Accrued expenses	4,620,000	1,173,000
Convertible preferred stock liability		1,671,000
Total current liabilities	5,609,000	4,353,000
Commitments and contingencies (Note 5)
Convertible preferred stock, $0.001 par value; 0 shares and 60,000,000 shares authorized as of December 31, 2019 and 2018, respectively; 0 shares and 24,000,000 shares issued and outstanding as of December 31, 2019 and 2018, respectively; liquidation value of $0 and $24,000 as of December 31, 2019 and 2018, respectively		23,073,000
Stockholders’ equity (deficit):
Common stock, $0.001 par value, 100,000,000 and 10,415,900 shares authorized as of December 31, 2019 and 2018, respectively; 13,788,982 and 611,226 shares issued and outstanding at December 31, 2019 and 2018, respectively	14,000	1,000
Additional paid-in capital	163,526,000	118,000
Accumulated deficit	(73,596,000)	(16,176,000)
Total stockholders’ equity (deficit)	89,944,000	(16,057,000)
Total liabilities, convertible preferred stock and stockholders’ equity	$ 95,553,000	$ 11,369,000

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($)	Dec. 31, 2019	Oct. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Convertible preferred stock, par value	$ 0.001		$ 0.001
Convertible preferred stock, shares authorized	0		60,000,000
Convertible preferred stock, shares issued	0		24,000,000
Convertible preferred stock, shares outstanding	0		24,000,000
Convertible preferred stock, liquidation value	$ 0		$ 24,000,000
Common stock, par value	$ 0.001	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000	10,415,900
Common stock, shares issued	13,788,982	13,788,982	611,226
Common stock, shares outstanding	13,788,982	13,788,982	611,226

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	11 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019
Operating expenses:
Research and development	$ 13,681	$ 21,346
General and administrative	1,481	5,294
Total operating expenses	15,162	26,640
Loss from operations	15,162	26,640
Other expenses (income), net	986	30,562
Net loss before tax	16,148	57,202
Income tax expense	28	218
Net loss and comprehensive loss	$ 16,176	$ 57,420
Net loss per share, basic and diluted	$ 36.45	$ 24.49
Weighted-average shares used to compute net loss per share, basic and diluted	443,767	2,344,191

Consolidated Statements of Conv

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($)	Total	Initial Public Offering	Common Stock	Common StockInitial Public Offering	Additional Paid-in Capital	Additional Paid-in CapitalInitial Public Offering	Accumulated Deficit	Accumulated DeficitInitial Public Offering	Convertible Preferred Stock
Beginning balance at Jan. 18, 2018	$ 0		$ 0		$ 0		$ 0
Beginning balance, shares at Jan. 18, 2018									0
Beginning balance at Jan. 18, 2018									$ 0
Beginning balance, shares at Jan. 18, 2018			0
Issuance of common stock	11,000		$ 1,000		10,000		0
Issuance of common stock, shares			611,226
Issuance of convertible preferred stock, net of issuance costs	0		$ 0		0		0		$ 22,973,000
Issuance of convertible preferred stock, net of issuance costs, shares			0						23,900,000
Conversion of convertible note into preferred stock	0		$ 0		0		0		$ 100,000
Conversion of convertible note into preferred stock, shares			0						100,000
Share-based compensation	108,000		$ 0		108,000		0
Net loss and comprehensive loss	(16,176,000)		0		0		(16,176,000)
Ending balance at Dec. 31, 2018	$ (16,057,000)		$ 1,000		118,000		(16,176,000)
Ending balance, shares at Dec. 31, 2018	24,000,000								24,000,000
Ending balance at Dec. 31, 2018	$ 23,073,000								$ 23,073,000
Ending balance, shares at Dec. 31, 2018			611,226
Issuance of common stock		$ 87,691,000		$ 6,000		$ 87,685,000		$ 0
Issuance of common stock, shares				6,100,390
Issuance of convertible preferred stock, net of issuance costs	0		$ 0		0		0		$ 26,673,000
Issuance of convertible preferred stock, net of issuance costs, shares									20,000,000
Conversion of convertible preferred stock into common stock upon completion of initial public offering	49,746,000		$ 7,000		49,739,000		0
Temporary Equity, Conversion of convertible preferred stock into common stock upon completion of initial public offering, shares									(44,000,000)
Temporary Equity, Conversion of convertible preferred stock into common stock upon completion of initial public offering									$ (49,746,000)
Conversion of convertible preferred stock into common stock upon completion of initial public offering, shares			7,077,366
Share-based compensation	389,000		$ 0		389,000		0
Capital contribution related to extinguishment of preferred stock liability	25,595,000		0		25,595,000		0		0
Net loss and comprehensive loss	(57,420,000)		0		0		(57,420,000)		$ 0
Ending balance at Dec. 31, 2019	$ 89,944,000		$ 14,000		$ 163,526,000		$ (73,596,000)
Ending balance, shares at Dec. 31, 2019	0								0
Ending balance at Dec. 31, 2019									$ 0
Ending balance, shares at Dec. 31, 2019			13,788,982

Consolidated Statements of Co_2

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	11 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019
Stock issuance costs		$ 3,083
Convertible Preferred Shares
Temporary equity, issuance costs	$ 235	0
Temporary equity, partial settlement of convertible preferred stock liability	$ 692
Temporary equity, settlement of convertible preferred stock liability		$ 6,673

Consolidated Statements of Cash

Consolidated Statements of Cash Flows	11 Months Ended	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2019USD ($)
Cash flows from operating activities:
Net loss	$ (16,176,000)	$ (57,420,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	6,000	17,000
Share-based compensation	108,000	389,000
Deferred tax assets	(20,000)	20,000
Revaluation of convertible preferred stock liability	979,000	30,597,000
Changes in operating assets and liabilities:
Prepaids and other current assets	(48,000)	(1,918,000)
Other assets		(72,000)
Accounts payable	1,509,000	(520,000)
Accrued expenses	1,173,000	3,447,000
Net cash used in operating activities	(12,469,000)	(25,460,000)
Cash flows from investing activities:
Purchases of property and equipment	(39,000)	(139,000)
Net cash used in investing activities	(39,000)	(139,000)
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock and convertible preferred stock liability, net of issuance costs	23,665,000	20,000,000
Proceeds from issuance of common stock		11,000
Proceeds from issuance of convertible note	100,000
Proceeds from initial public offering net of issuance costs		87,691,000
Net cash provided by financing activities	23,765,000	107,702,000
Net increase in cash and cash equivalents, and restricted cash	11,257,000	82,103,000
Cash and cash equivalents, and restricted cash at beginning of year (period)		11,257,000
Cash and cash equivalents, and restricted cash at end of year (period)	11,257,000	93,360,000
Components of cash and cash equivalents, and restricted cash:
Cash and cash equivalents	11,234,000	93,335,000
Restricted cash	23,000	25,000
Cash and cash equivalents, and restricted cash at end of year (period)	11,257,000	93,360,000
Supplemental disclosures of noncash information:
Conversion of convertible note into preferred stock	$ 100,000
Conversion of convertible preferred stock into common stock at close of initial public offering		49,746,000
Capital contribution related to extinguishment of preferred stock liability		25,595,000
Property and equipment purchases included in accounts payable		55,000
Cash paid for taxes		$ 106,000

Organization and Basis of Prese

Organization and Basis of Presentation	12 Months Ended
	Dec. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Basis of Presentation	1. Organization and Basis of Presentation Description of Business 89bio, Inc. (“89bio” or the “Company”) is a clinical-stage biopharmaceutical company focused on the development and commercialization of innovative therapies for the treatment of liver and cardio-metabolic diseases. The Company’s lead product candidate, BIO89-100, a specifically engineered glycoPEGylated analog of fibroblast growth factor 21, is currently being developed for the treatment of nonalcoholic steatohepatitis. 89Bio Ltd. was incorporated in Israel in January 2018 and has two wholly owned subsidiaries: 89bio Management, Inc., located in San Francisco, California and UAB 89bio Lithuania, located in Vilnius, Lithuania. 89bio, Inc. was formed as a Delaware corporation on June 28, 2019, for the purpose of completing an initial public offering (“IPO”) and related transactions in order to carry on the business of 89Bio Ltd. The Company completed an internal reorganization transaction in September 2019, pursuant to which 89Bio Ltd. became a wholly owned subsidiary of 89bio, Inc. (the “Reorganization”). As part of the Reorganization, all of the equity holders of 89Bio Ltd. Exchanged 100% of the equity of 89Bio Ltd. for 100% of the equity of 89bio, Inc. The Reorganization was considered a transaction between entities under common control. As a result, the accompanying consolidated financial statements have been retrospectively adjusted to reflect the Reorganization. Initial Public Offering On November 13, 2019, 89bio, Inc. completed the IPO, pursuant to which it issued and sold an aggregate of 6,100,390 shares of common stock (inclusive of 795,703 shares pursuant to the underwriters’ option to purchase additional shares) at the IPO price of $16.00 per share, resulting in net proceeds of $87.7 million after deducting underwriting discounts and commissions of $6.8 million and other offering expenses of $3.1 million. Upon the closing of the IPO, the Company’s outstanding convertible preferred stock automatically converted into 7,077,366 shares of common stock of 89bio, Inc. based on a proportional adjustment to the conversion ratio of the convertible preferred stock on a 1-for-6.217 basis. Reverse Stock Split On October 24, 2019, 89bio, Inc.’s board of directors approved an amendment to the amended and restated certificate of incorporation of 89bio, Inc. to effect a 1 for 6.217 reverse split (“Reverse Split”) of shares of the common stock of 89bio, Inc. and a proportional adjustment to the conversion ratio of the convertible preferred stock, which was effected on October 25, 2019. The par value and authorized shares of common stock, and the par value, authorized and outstanding shares of the convertible preferred stock were not adjusted as a result of the Reverse Split. All of the share and per share information for 89bio, Inc. included in the accompanying consolidated financial statements has been adjusted to reflect the Reverse Split. Liquidity The accompanying consolidated financial statements have been prepared assuming the Company will continue as a going concern, which contemplates the realization of assets and liquidation of liabilities in the normal course of business. To date, the Company has not generated revenues from its activities and has incurred substantial operating losses. Management expects the Company to continue to generate substantial operating losses for the foreseeable future until it completes development of its products and seeks regulatory approvals to market such products. The Company had cash and cash equivalents of $93.3 million as of December 31, 2019. Management expects to continue to fund its operations primarily through utilization of its current financial resources and through additional raises of capital. The Company intends to raise such capital through the issuance of additional equity financing and/or debt financing. However, if such financing is not available at adequate levels, the Company will need to reevaluate its operating plan and may be required to delay the development of its products. The Company expects that its cash and cash equivalents as of December 31, 2019 will be sufficient to fund operating expenses and capital expenditure requirements for a period of at least one year from the date these audited consolidated financial statements are filed with the Securities and Exchange Commission (“SEC”).

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“U.S. GAAP”). Principles of Consolidation The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Foreign Currencies Certain transactions during the period from January 18, 2018 (inception) to December 31, 2018 and the year ended December 31, 2019 were denominated in the Euro or Israeli New Shekel. Gains and losses from foreign currency transactions were not material for all periods presented and are reflected in the consolidated statement of operations and comprehensive loss as a component of other expenses (income), net. The financial statements of UAB 89bio Lithuania use the Euro as the functional currency. The re-measurement from Euros to U.S. dollars results in translation gain and loss adjustments, which were not material for all periods presented. Accordingly, the Company has not presented translation gain and loss adjustments separately as a component of comprehensive loss. Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of expenses during the reporting period. Significant estimates and assumptions made in the accompanying consolidated financial statements include but are not limited to the fair value of stock options, the convertible preferred stock liability and certain accruals. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates. Fair Value Measurements Financial assets and liabilities are recorded at fair value on a recurring basis in the balance sheets. The carrying values of Company’s financial assets and liabilities, including cash and cash equivalents, restricted cash, prepaid and other current assets, accounts payable, and accrued expenses approximate to their fair value due to the short-term maturity of these instruments. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the reporting date. Assets and liabilities recorded at fair value are categorized based upon the level of judgment associated with the inputs used to measure their fair value. Hierarchical levels are directly related to the amount of subjectivity with the inputs to the valuation of these assets or liabilities as follows: Level 1 —Observable inputs such as unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date; Level 2 —Inputs (other than quoted prices included in Level 1) are either directly or indirectly observable inputs for similar assets or liabilities. These include quoted prices for identical or similar assets or liabilities in active markets and quoted prices for identical or similar assets or liabilities in markets that are not active; Level 3 —Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Convertible Preferred Stock Liability The freestanding instruments related to the commitment by the Series A convertible preferred stockholders to purchase and by the Company to sell its Series A convertible preferred stock in subsequent closings, contingent upon the achievement of certain developmental milestones and approval by the board of directors, at a fixed price per stock, were considered a liability (or an asset), measured at fair value as the shares underlying the rights contained liquidation preferences upon certain “deemed liquidation events” that were not solely within the Company’s control and which were considered in-substance contingent redemption features (refer to Note 7 for further discussion on the redemption rights of the convertible preferred stock). The instruments were subject to revaluation at each balance sheet date until settlement or extinguishment, with revaluations recognized as either a component of other expenses (income), net in the consolidated statements of operations and comprehensive loss, or additional paid-in capital in the consolidated balance sheets. Cash and Cash Equivalents and Restricted Cash The Company considers all highly liquid investments purchased with original maturities of three months or less from the purchase date to be cash equivalents. Cash equivalents consist primarily of amounts invested in money market accounts and are stated at fair value. Restricted cash consists of a money market account that serves as collateral for the Company’s operating lease agreement for its facility in Israel. Concentrations of Credit Risk Financial Other Risks and Uncertainties The Company’s future results of operations involve a number of other risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, the Company’s early stages of clinical drug development; the Company’s ability to advance product candidates into, and successfully complete, clinical trials on the timelines it projects; the Company’s ability to adequately demonstrate sufficient safety and efficacy of its product candidates; the Company’s ability to enroll patients in its ongoing and future clinical trials; the Company’s ability to successfully manufacture and supply its product candidates for clinical trials; the Company’s ability to obtain additional capital to finance its operations; uncertainties related to the projections of the size of patient populations suffering from the diseases the Company is targeting; the Company’s ability to obtain, maintain, and protect its intellectual property rights; developments relating to the Company’s competitors and its industry, including competing product candidates and therapies; general economic and market conditions; and other risks and uncertainties. The Company’s product candidates will require approvals from the U.S. Food and Drug Administration and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any product candidates will receive the necessary approvals. If the Company was denied approval, approval was delayed or the Company was unable to maintain approval for any product candidate, it could have a materially adverse impact on the Company. Property Property Upon retirement or sale of the assets, the cost and related accumulated depreciation and amortization are removed from the balance sheet and the resulting gains or losses are recorded to the statements of operations. Impairment The Company periodically Leases The Company leases Research and Research The Company accrues for these Share-Based Compensation The Company measures The Company estimates The Company recognizes The Black-Scholes comparable publicly traded biotechnology companies Deferred Offering Costs Deferred offering costs, consisting of legal, accounting, and filing fees directly relating to the IPO, were capitalized and upon completion of the IPO, approximately $3.1 million of deferred offering costs were offset against the IPO proceeds in additional paid-in capital. For the year ended December 31, 2018, the Company did not incur any deferred offering costs. Income Taxes Income Basic and Basic loss per share Comprehensive The Company’s comprehensive Segment Reporting The Company has one operating Recently Adopted Accounting Standards In May 2014, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) 2014-09— Revenue from contracts with customers In June 2018, the FASB issued ASU No. 2018-07 Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting Recent Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02— Leases In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement , which amends ASC 820, Fair Value Measurement. This ASU modifies the disclosure requirements for fair value measurements by removing, modifying, or adding certain disclosures. The standard is effective for public and nonpublic entities for fiscal years beginning after December 15, 2019, with early adoption permitted for the removed disclosures and delayed adoption until fiscal years beginning after December 15, 2019 permitted for the new disclosures. The removed and modified disclosures will be adopted on a retrospective basis and the new disclosures will be adopted on a prospective basis. The Company is currently evaluating the impact of this standard on its consolidated financial statements and related disclosures . In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes after December 15, 2020 and for nonpublic entities after December 15, 2021 financial statements and related disclosures

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The fair value of the Company’s financial liabilities measured at fair value on a recurring basis by level within the fair value hierarchy are as follows (in thousands): As of December 31, 2019 Level 1 Level 2 Level 3 Total Liabilities: Convertible preferred stock liability $ — $ — $ — $ — Total financial liabilities $ — $ — $ — $ — As of December 31, 2018 Level 1 Level 2 Level 3 Total Liabilities: Convertible preferred stock liability $ — $ — $ 1,671 $ 1,671 Total financial liabilities $ — $ — $ 1,671 $ 1,671 The changes in the fair value of the Company’s Level 3 financial liabilities, which are measured on a recurring basis are as follows (in thousands): As of December 31, 2019 2018 Beginning balance $ 1,671 $ — Recognition of convertible preferred stock liability upon issuance of convertible preferred stock — 638 Revaluation of convertible preferred stock liability recorded in other expenses (income), net 30,597 979 Partial settlement of convertible preferred stock liability upon second closing — 54 Partial settlement of convertible preferred stock liability upon third closing (6,673 ) — Capital contribution related to extinguishment of preferred stock liability (25,595 ) — Ending balance $ — $ 1,671 The Company’s convertible preferred stock liability resulted from the initial sale of Series A convertible preferred stock where the investors’ committed to purchase additional shares of Series A convertible preferred stock in subsequent closings, contingent upon the achievement by the Company of certain development milestones and approval by the board of directors. The investors’ commitment to purchase and the Company’s commitment to sell shares of Series A convertible preferred stock represented a freestanding instrument accounted for at fair value and re-measured at each reporting date. The Company estimated the fair value of this commitment using the Black Scholes option pricing model using the following assumptions: Period from January 18, 2018 Year Ended (inception) to December 31, December 31, 2019 2018 Stock price $0.99-$2.57 $0.96-$0.99 Exercise price $ 1.00 $ 1.00 Expected term (years) 0.00-2.25 0.25-3.21 Expected volatility 72.0 % 70.0-72.0% Risk-free interest rate 0.0-2.4% 2.1-2.9% The main factor impacting the change in fair value of the convertible preferred stock liability was the estimated stock price of the preferred stock liability. Refer to Note 7 for further discussion on the convertible preferred stock liability and the accounting upon extinguishment of the preferred stock liability.

Consolidated Balance Sheet Comp

Consolidated Balance Sheet Components	12 Months Ended
	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Consolidated Balance Sheet Components	4. Consolidated Balance Sheet Components Property and Equipment, Net Property and equipment, net consists of the following (in thousands): As of December 31, 2019 2018 Computer software and electronic equipment $ 67 $ 33 Furniture and office equipment 111 6 Total property and equipment 178 39 Less: accumulated depreciation (23 ) (6 ) Total property and equipment, net $ 155 $ 33 Depreciation expense for property and equipment was $17,000 for the year ended December 31, 2019 and $6,000 for the period from January 18, 2018 (inception) to December 31, 2018. Accrued Expenses Accrued expenses consist of the following (in thousands): As of December 31, 2019 2018 Accrued research and development expenses $ 2,326 $ 890 Accrued employee and related expenses 1,396 283 Accrued professional and legal fees 573 — Accrued other 325 — Total accrued expenses $ 4,620 $ 1,173

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	5. Commitments and Contingencies Leases In May 2018, the Company entered In December 2019, the Company entered into an operating lease for its headquarters in San Francisco. The lease term is for 24 months, expiring in January 2022, and monthly lease payments are approximately $17,500. Future minimum 2020 $ 226 2021 216 Total future minimum annual payments $ 442 Rent expense was $159,000 for year ended December 31, 2019 and $39,000 during the period from January 18, 2018 (inception) to December 31, 2018. The Company has security deposit balances of $95,000, which are included in restricted cash and other assets in the consolidated balance sheets as of December 31, 2019. The security deposit balance of $23,000 was included in restricted cash in the consolidated balance sheets as of December 31, 2018. Asset Transfer and License Agreement with Teva Pharmaceutical Industries Ltd In April 2018, the Company concurrently entered into two Asset Transfer and License Agreements (the “Teva Agreements”) with Teva Pharmaceutical Industries Ltd (“Teva”) under which it acquired certain patents and intellectual property relating to two programs: (1) Teva’s glycoPEGylated FGF21 program, including the compound TEV-47948 (BIO89-100), a glycoPEGylated long-acting FGF21 and (2) Teva’s development program of small molecule inhibitors of Fatty Acid Synthase. Pursuant to the Teva Agreements, the Company paid Teva an initial nonrefundable upfront payment of $6.0 million and the Company could be obligated to pay Teva up to $67.5 million under each program, for a total of $135.0 million, upon the achievement of certain clinical development and commercial milestones. In addition, the Company is obligated to pay Teva tiered royalties at percentages in the low-to-mid single-digits on worldwide net sales on all products containing the Teva compounds. The Teva Agreements can be terminated (i) by the Company without cause, after the first anniversary of the effective date, upon 120 days’ written notice to Teva, (ii) by either party, if the other party materially breaches any of its obligations under the Agreements and fails to cure such breach within 60 days after receiving notice thereof, or (iii) by either party, if a bankruptcy petition is filed against the other party and is not dismissed within 60 days. In addition, Teva can also terminate the agreement related to the Company’s glycoPEGylated FGF21 program in the event the Company, or any of its affiliates or sublicensees, challenges any of the Teva patents licensed to the Company, and the challenge is not withdrawn within 30 days of written notice from Teva. 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 total consideration transferred to Teva as research and development expense in the consolidated statements of operations and comprehensive loss because the acquired technology represented in-process research and development and had no alternative future use. During the period from January 18, 2018 (inception) to December 31, 2018, the Company recognized an up-front license payment of $6.0 million in research and development expenses under the Teva Agreements in its consolidated statements of operations and there were no such license payment expenses related to the Teva Agreements during the year ended December 31, 2019.

Convertible Note

Convertible Note	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Convertible Note	6. Convertible Note In March 2018, the Company entered into a Convertible Loan Agreement (the “Convertible Note”) with a principal amount of $100,000 and a fixed interest rate of 8% per annum. The Convertible Note was automatically convertible into the Company’s next equity financing, or upon an earlier event of default. In April 2018, the entire amount outstanding converted into 100,000 shares of Series A convertible preferred stock upon the initial closing of the Series A financing.

Convertible Preferred Stock

Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2019
Temporary Equity Disclosure [Abstract]
Convertible Preferred Stock	7. Convertible Preferred Stock In April 2018, the Company entered into the Series A Share Purchase Agreement (the “ Series A SPA”), pursuant to which the investors committed to invest an aggregate amount of up to $60.0 million for the issuance of shares of Series A convertible preferred stock at a price of $1.00 per share. The initial closing occurred on April 16, 2018, and the Company issued 14,900,000 shares of Series A convertible preferred stock at a price per share of $1.00 for net cash proceeds of $14.7 million. The investors also committed to purchase 15,000,000 and 30,000,000 shares of Series A convertible preferred stock at a price of $1.00 per share in second and third closings, respectively, contingent upon the achievement by the Company of certain development milestones and approval by the board of directors. The investors’ commitment to purchase and the Company’s commitment to sell shares of Series A convertible preferred stock represent a freestanding instrument accounted for at fair value and re-measured at each reporting date. The Company estimates the fair value of this commitment using the Black-Scholes option pricing model. On the date of the initial closing, the Company recorded the commitments associated with the second and third closings of the Series A convertible preferred stock at a net value of $638,000. For the year ended December 31, 2019 and for the period from January 18, 2018 (inception) to December 31, 2018, the Company recorded an expense of $30.6 million and $1.0 million, respectively, for the revaluation of the convertible preferred stock liability, within other expenses (income), net in the consolidated statements of operations and comprehensive loss. In December 2018, the Series A convertible preferred stockholders partially accelerated the second closing and the Company issued 9,000,000 shares of Series A convertible preferred stock at a price of $1.00 per share and received net proceeds of $9.0 million. In June 2019, the Company and the Series A convertible preferred stockholders agreed to issue the remaining 6,000,000 shares of Series A convertible preferred stock at a price of $1.00 per share related to the second closing, and to partially accelerate 14,000,000 shares of Series A convertible preferred stock at a price of $1.00 per share related to the third closing. The shares were issued and the aggregate net proceeds of $20.0 million were received in June and July 2019. In September 2019, the Company completed an internal reorganization transaction pursuant to which 89Bio Ltd. became a wholly owned subsidiary of 89bio, Inc. As part of the Reorganization, all outstanding convertible preferred shares of 89Bio Ltd. were exchanged into shares of convertible preferred stock of 89bio, Inc. On October 25, 2019, the Company and the Series A preferred stockholders amended the Series A SPA, and the parties agreed that the Series A SPA would terminate upon consummation of the Company’s IPO. Upon the completion of the Company’s IPO on November 13, 2019, the remaining 16,000,000 shares of convertible preferred stock that were previously issuable under the third closing were no longer issuable. Accordingly, the preferred stock liability was extinguished and because the transaction occurred between related parties, the resulting $25.6 million was accounted for as a capital contribution by the preferred stockholders. Additionally, immediately prior to the completion of the Company’s IPO, all outstanding shares of convertible preferred stock automatically converted into 7,077,366 shares of common stock and the related carrying value was reclassified to common stock and additional paid-in capital. Accordingly, there were no shares of convertible preferred stock outstanding as of December 31, 2019. Convertible preferred stock as of December 31, 2018 consisted of the following: Shares Shares Issued and Carrying Liquidation Authorized Outstanding Value Value Series A 60,000,000 24,000,000 $ 23,073,000 $ 24,000,000 Total 60,000,000 24,000,000 $ 23,073,000 $ 24,000,000 The Company’s certificate of incorporation Although the convertible equity ( stock

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Common Stock	8. Common Stock The Company is authorized to issue a total of 100,000,000 shares of common stock with a par value of $0.001 per share, 13,788,982 of which were issued and outstanding as of December 31, 2019. Total common stock reserved for issuance is summarized as follows: As of December 31, 2019 2018 Series A convertible preferred stock outstanding, as converted — 3,860,383 Options issued and outstanding 1,320,243 591,448 Shares available for future option grants 1,523,950 472,714 Total common stock reserved for issuance 2,844,193 4,924,545

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share-Based Compensation	9. Share-Based Compensation Equity Incentive Plans In 2018, the Company’s board of directors adopted the 89Bio Ltd. 2018 Equity Incentive Plan (the “2018 Plan”). In connection with the Reorganization, in September 2019, the Company’s board of directors approved the 2019 Equity Incentive Plan (the “2019 Plan”), which became effective on September 17, 2019. From and after the effective date of the 2019 Plan, the Company will no longer be making any future awards under the 2018 Plan. The Company initially reserved 2,844,193 shares of common stock for issuance under the 2019 Plan. In addition, the number of shares of common stock reserved for issuance under the 2019 Plan will automatically increase on the first day of January for a period of up to ten years, commencing on January 1, 2020, in an amount equal to 4% of the total number of shares of the Company’s capital stock outstanding on the immediately preceding December 31, or a lesser number of shares determined by the Company’s board of directors. As of December 31, 2019, there were 1,523,950 shares of common stock available for issuance as future option grants under the 2019 Plan. The Board determines the period over which options become exercisable and options generally vest over a four-year period, with 25% of options vesting on the first anniversary of employment, and thereafter, the remaining options vesting quarterly, over the following 36-month period. The options will expire within ten years from the date of grant. The exercise price of awards granted will not be less than the estimated fair value of the shares on the date of grant. Employees Share Purchase Plan (ESPP) In October 2019, the Company adopted the 2019 Employee Stock Purchase Plan (“ESPP”), which became effective following the date of the IPO. The Company initially reserved 225,188 shares of common stock for purchase under the ESPP. The number of shares of common stock reserved for issuance under the 2019 ESPP will automatically increase on the first day of January for a period of up to ten years, in an amount equal to 1% of the total number of shares of the Company’s common stock outstanding on the immediately preceding December 31, or a lesser number of shares determined by the Company’s board of directors. Purchases will be accomplished through the participation of discrete offering periods. Each offering will be no more than 27 months long. For each offering period, ESPP participants will purchase shares of common stock at a price per share equal to 85% of the lesser of the fair market value of the Company’s common stock on (1) the first trading day of the applicable offering period or (2) the last trading day of each purchase period the applicable offering period. As of December 31, 2019, no offering periods have commenced under the ESPP and 225,188 shares of common stock remained available for issuance under the ESPP. The Company recorded share-based compensation for the periods indicated as follows (in thousands): Period from January 18, 2018 Year Ended (inception) to December 31, December 31, 2019 2018 Research and development $ 30 $ 13 General and administrative 359 95 Total share-based compensation $ 389 $ 108 The fair value of option awards granted for the periods indicated was estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions: Period from January 18, 2018 Year Ended (inception) to December 31, December 31, 2019 2018 Expected term (years) 5.88-6.11 5.9 Expected volatility 61.8-87.6% 73.2 % Risk-free interest rate 1.6-2.6% 3.1 % Expected dividend — — The following table summarizes stock option activity under the 2019 Plan: Weighted Weighted Average Average Remaining Aggregate Number of Exercise Contractual Intrinsic Options Price Term Value (In years) (In thousands) Balance outstanding as of December 31, 2018 591,448 $ 1.93 9.87 $ — Granted 742,285 4.37 Exercised — — Cancelled (13,490 ) 1.93 Balance outstanding as of December 31, 2019 1,320,243 $ 3.34 9.23 $ 30,353 Exercisable as of December 31, 2019 235,188 $ 5,730 During the year ended December 31, 2019, the estimated total grant date fair value of options vested was $296,000. Options granted Included during

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes Tax Rates Applicable to the Income of the Company and its Subsidiaries As a result of the Reorganization described in Note 1, as of December 31, 2019, the Company is taxed according to U.S. federal and state tax laws and Israeli tax laws. Prior to the Reorganization, for the year ended December 31, 2018, the Company was taxed according to Israeli tax laws. The statutory tax rates applicable to the income of the Company and its subsidiaries are as follows: Period from January 18, 2018 Year Ended (inception) to December 31, December 31, 2019 2018 89bio, Inc. 21 % — 89Bio Ltd 23 % 23 % 89bio Management, Inc. 21 % 21 % UAB 89bio Lithuania 15 % 15 % The expense for income Period from January 18, 2018 Year Ended (inception) to December 31, December 31, 2019 2018 Current: Federal $ 167 $ — State 1 — Foreign 30 48 Total 198 48 Deferred: Federal 20 — State — — Foreign — (20 ) Total 20 (20 ) Income tax expense $ 218 $ 28 Deferred Deferred As of December 31, 2019 2018 Israel net operating loss carryforwards $ 4,328 $ 1,536 U.S. net operating loss carryforwards 1,916 — Research and development expenses 3,327 1,966 Other 451 20 Total deferred tax assets 10,022 3,522 Less: valuation allowance (10,022 ) (3,502 ) Net deferred tax assets $ — $ 20 As Available Losses and Credits As of December 31, 2019, the Company has an accumulated As of December 31, 2019, the Company has state research and development credit carryforwards of approximately $156,000, which will carryforward indefinitely. Loss from Continuing Operations, Before Taxes on Income The Company recorded a loss from continuing operations, before taxes on income for the periods indicated as follows (in thousands): Period from January 18, 2018 Year Ended (inception) to December 31, December 31, 2019 2018 United States $ (19,502 ) $ 50 Lithuania 200 50 Israel (37,900 ) (16,248 ) Net loss before tax $ (57,202 ) $ (16,148 ) Reconciliation of Income Tax Expense The reconciliation Period from January 18, 2018 Year Ended (inception) to December 31, December 31, 2019 2018 Income tax expense computed at statutory rates $ (13,095 ) $ (3,714 ) Change in valuation allowance 6,520 3,502 Change in Israel effective tax rate due to the 2019 reorganization 734 — Revaluation of convertible preferred share liability 6,039 226 Other 20 14 Income tax expense $ 218 $ 28 Utilization of the U.S. federal and state net operating losses and credit carryforwards may be subject to an annual limitation provided for in Section 382 of the Internal Revenue Code and similar state codes. Any annual limitation could result in a deferral of the utilization of the net operating loss and credit carryforwards. Unrecognized Tax Benefits During the year ended December 31, 2019, the amount of gross unrecognized tax benefits increased by $39,000 from a balance at the beginning of the year of $0. If the total amount of unrecognized tax benefits was recognized, it would not have an impact to the effective tax rate as it would be offset by the reversal of related deferred tax assets which are subject to a full valuation allowance. The Company recognizes interest and penalties related to uncertain tax positions as part of the income tax provision. As of December 31, 2019 and 2018, such interest and penalties have not been material. The Company is subject to taxation in the United States, California and several foreign jurisdictions. To date, the Company has not been subject to any federal or state income tax audits. As of December 31, 2019, all tax years remain open to examination.

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2019
Earnings Per Share [Abstract]
Net Loss Per Share	11. Net Loss Per Share The following outstanding potentially dilutive common stock equivalents have been excluded from the calculation of diluted net loss per share for the periods presented due to their anti-dilutive effect: Period from January 18, 2018 Year Ended (inception) to December 31, December 31, 2019 2018 Convertible preferred stock, as converted — 3,860,383 Stock options to purchase common stock 1,320,243 591,448 Shares available for future option grants 1,523,950 472,714 Total 2,844,193 4,924,545

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2019
Related Party Transactions [Abstract]
Related Party Transactions	12. Related Party Transactions The Company incurred $170,000 and $147,000 in professional consulting services expense related to certain members of the board of directors for the year ended December 31, 2019 and for the period from January 18, 2018 (inception) to December 31, 2018, respectively, which were recorded within research and development expenses on the Company’s consolidated statements of operations and comprehensive loss. The related party liability balance was $11,000 and $23,000 as of December 31, 2019 and 2018, respectively, which was recorded within accounts payable and accrued expenses on the Company’s consolidated balance sheets. The Company and the Series A preferred stockholders amended the Series A SPA on October 25, 2019, and the parties agreed that the Series A SPA would terminate upon consummation of the Company’s IPO. Upon the completion of the Company’s IPO on November 13, 2019, the remaining 16,000,000 shares of convertible preferred stock that were issuable were no longer issuable. Accordingly, the preferred stock liability was extinguished and because the transaction occurred between related parties, the resulting $25.6 million was accounted for as a capital contribution by the preferred stockholders and recorded as part of additional paid-in capital on the consolidated balance sheets (see Note 7).

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2019
Selected Quarterly Financial Information [Abstract]
Selected Quarterly Financial Data (Unaudited)	13. Selected Quarterly Financial Data (Unaudited) Selected quarterly results from operations for the year ended December 31, 2019 is as follows: Three Months Ended, December 31, September 30, June 30, March 31, (in thousands, except per share data) 2019 Loss from operations $ (9,611 ) $ (8,198 ) $ (3,947 ) $ (4,884 ) Net loss and comprehensive loss (19,283 ) (18,725 ) (14,525 ) (4,887 ) Net loss per share, basic and diluted $ (2.58 ) $ (30.63 ) $ (23.76 ) $ (8.00 ) Selected quarterly results from operations for the period from January 18, 2018 (inception) to December 31, 2018 is as follows: Period from January 18, 2018 Three Months Ended, (inception) to December 31, September 30, June 30, March 31, (in thousands, except per share data) 2018 Loss from operations $ (4,408 ) $ (3,786 ) $ (6,968 ) $ — Net loss and comprehensive loss (4,638 ) (4,165 ) (7,373 ) — Net loss per share, basic and diluted $ (7.59 ) $ (6.81 ) $ (13.55 ) $ —

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“U.S. GAAP”).
Principles of Consolidation	Principles of Consolidation The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.
Foreign Currencies	Foreign Currencies Certain transactions during the period from January 18, 2018 (inception) to December 31, 2018 and the year ended December 31, 2019 were denominated in the Euro or Israeli New Shekel. Gains and losses from foreign currency transactions were not material for all periods presented and are reflected in the consolidated statement of operations and comprehensive loss as a component of other expenses (income), net. The financial statements of UAB 89bio Lithuania use the Euro as the functional currency. The re-measurement from Euros to U.S. dollars results in translation gain and loss adjustments, which were not material for all periods presented. Accordingly, the Company has not presented translation gain and loss adjustments separately as a component of comprehensive loss.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of expenses during the reporting period. Significant estimates and assumptions made in the accompanying consolidated financial statements include but are not limited to the fair value of stock options, the convertible preferred stock liability and certain accruals. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates.
Fair Value Measurements	Fair Value Measurements Financial assets and liabilities are recorded at fair value on a recurring basis in the balance sheets. The carrying values of Company’s financial assets and liabilities, including cash and cash equivalents, restricted cash, prepaid and other current assets, accounts payable, and accrued expenses approximate to their fair value due to the short-term maturity of these instruments. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the reporting date. Assets and liabilities recorded at fair value are categorized based upon the level of judgment associated with the inputs used to measure their fair value. Hierarchical levels are directly related to the amount of subjectivity with the inputs to the valuation of these assets or liabilities as follows: Level 1 —Observable inputs such as unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date; Level 2 —Inputs (other than quoted prices included in Level 1) are either directly or indirectly observable inputs for similar assets or liabilities. These include quoted prices for identical or similar assets or liabilities in active markets and quoted prices for identical or similar assets or liabilities in markets that are not active; Level 3 —Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.
Convertible Preferred Stock Liability	Convertible Preferred Stock Liability The freestanding instruments related to the commitment by the Series A convertible preferred stockholders to purchase and by the Company to sell its Series A convertible preferred stock in subsequent closings, contingent upon the achievement of certain developmental milestones and approval by the board of directors, at a fixed price per stock, were considered a liability (or an asset), measured at fair value as the shares underlying the rights contained liquidation preferences upon certain “deemed liquidation events” that were not solely within the Company’s control and which were considered in-substance contingent redemption features (refer to Note 7 for further discussion on the redemption rights of the convertible preferred stock). The instruments were subject to revaluation at each balance sheet date until settlement or extinguishment, with revaluations recognized as either a component of other expenses (income), net in the consolidated statements of operations and comprehensive loss, or additional paid-in capital in the consolidated balance sheets.
Cash and Cash Equivalents and Restricted Cash	Cash and Cash Equivalents and Restricted Cash The Company considers all highly liquid investments purchased with original maturities of three months or less from the purchase date to be cash equivalents. Cash equivalents consist primarily of amounts invested in money market accounts and are stated at fair value. Restricted cash consists of a money market account that serves as collateral for the Company’s operating lease agreement for its facility in Israel.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial
Other Risks and Uncertainties	Other Risks and Uncertainties The Company’s future results of operations involve a number of other risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, the Company’s early stages of clinical drug development; the Company’s ability to advance product candidates into, and successfully complete, clinical trials on the timelines it projects; the Company’s ability to adequately demonstrate sufficient safety and efficacy of its product candidates; the Company’s ability to enroll patients in its ongoing and future clinical trials; the Company’s ability to successfully manufacture and supply its product candidates for clinical trials; the Company’s ability to obtain additional capital to finance its operations; uncertainties related to the projections of the size of patient populations suffering from the diseases the Company is targeting; the Company’s ability to obtain, maintain, and protect its intellectual property rights; developments relating to the Company’s competitors and its industry, including competing product candidates and therapies; general economic and market conditions; and other risks and uncertainties. The Company’s product candidates will require approvals from the U.S. Food and Drug Administration and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any product candidates will receive the necessary approvals. If the Company was denied approval, approval was delayed or the Company was unable to maintain approval for any product candidate, it could have a materially adverse impact on the Company.
Property and Equipment, Net	Property Property Upon retirement or sale of the assets, the cost and related accumulated depreciation and amortization are removed from the balance sheet and the resulting gains or losses are recorded to the statements of operations.
Impairment of Long-Lived Assets	Impairment The Company periodically
Leases	Leases The Company leases
Research and Development Expenses and Accrued Research and Development Expenses	Research and Research The Company accrues for these
Share-Based Compensation	Share-Based Compensation The Company measures The Company estimates The Company recognizes The Black-Scholes comparable publicly traded biotechnology companies
Deferred Offering Costs	Deferred Offering Costs Deferred offering costs, consisting of legal, accounting, and filing fees directly relating to the IPO, were capitalized and upon completion of the IPO, approximately $3.1 million of deferred offering costs were offset against the IPO proceeds in additional paid-in capital. For the year ended December 31, 2018, the Company did not incur any deferred offering costs.
Income Taxes	Income Taxes Income
Basic and Diluted Net Loss per Share	Basic and Basic loss per share
Comprehensive Loss	Comprehensive The Company’s comprehensive
Segment Reporting	Segment Reporting The Company has one operating
Recently Adopted Accounting Standards	Recently Adopted Accounting Standards In May 2014, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) 2014-09— Revenue from contracts with customers In June 2018, the FASB issued ASU No. 2018-07 Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting
Recent Accounting Pronouncements	Recent Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02— Leases In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement , which amends ASC 820, Fair Value Measurement. This ASU modifies the disclosure requirements for fair value measurements by removing, modifying, or adding certain disclosures. The standard is effective for public and nonpublic entities for fiscal years beginning after December 15, 2019, with early adoption permitted for the removed disclosures and delayed adoption until fiscal years beginning after December 15, 2019 permitted for the new disclosures. The removed and modified disclosures will be adopted on a retrospective basis and the new disclosures will be adopted on a prospective basis. The Company is currently evaluating the impact of this standard on its consolidated financial statements and related disclosures . In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes after December 15, 2020 and for nonpublic entities after December 15, 2021 financial statements and related disclosures

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Summary of Liabilities Measured at Fair Value on Recurring Basis	The fair value of the Company’s financial liabilities measured at fair value on a recurring basis by level within the fair value hierarchy are as follows (in thousands): As of December 31, 2019 Level 1 Level 2 Level 3 Total Liabilities: Convertible preferred stock liability $ — $ — $ — $ — Total financial liabilities $ — $ — $ — $ — As of December 31, 2018 Level 1 Level 2 Level 3 Total Liabilities: Convertible preferred stock liability $ — $ — $ 1,671 $ 1,671 Total financial liabilities $ — $ — $ 1,671 $ 1,671
Summary of Changes in Fair Value of Level 3 Liabilities	The changes in the fair value of the Company’s Level 3 financial liabilities, which are measured on a recurring basis are as follows (in thousands): As of December 31, 2019 2018 Beginning balance $ 1,671 $ — Recognition of convertible preferred stock liability upon issuance of convertible preferred stock — 638 Revaluation of convertible preferred stock liability recorded in other expenses (income), net 30,597 979 Partial settlement of convertible preferred stock liability upon second closing — 54 Partial settlement of convertible preferred stock liability upon third closing (6,673 ) — Capital contribution related to extinguishment of preferred stock liability (25,595 ) — Ending balance $ — $ 1,671
Summary of Fair Value Assumptions	The Company estimated the fair value of this commitment using the Black Scholes option pricing model using the following assumptions: Period from January 18, 2018 Year Ended (inception) to December 31, December 31, 2019 2018 Stock price $0.99-$2.57 $0.96-$0.99 Exercise price $ 1.00 $ 1.00 Expected term (years) 0.00-2.25 0.25-3.21 Expected volatility 72.0 % 70.0-72.0% Risk-free interest rate 0.0-2.4% 2.1-2.9%

Consolidated Balance Sheet Co_2

Consolidated Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net consists of the following (in thousands): As of December 31, 2019 2018 Computer software and electronic equipment $ 67 $ 33 Furniture and office equipment 111 6 Total property and equipment 178 39 Less: accumulated depreciation (23 ) (6 ) Total property and equipment, net $ 155 $ 33
Schedule of Accrued Expenses	Accrued expenses consist of the following (in thousands): As of December 31, 2019 2018 Accrued research and development expenses $ 2,326 $ 890 Accrued employee and related expenses 1,396 283 Accrued professional and legal fees 573 — Accrued other 325 — Total accrued expenses $ 4,620 $ 1,173

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments Under Non-cancellable Operating Lease Obligations	Future minimum 2020 $ 226 2021 216 Total future minimum annual payments $ 442

Convertible Preferred Stock (Ta

Convertible Preferred Stock (Tables)	12 Months Ended
	Dec. 31, 2019
Temporary Equity Disclosure [Abstract]
Schedule of Convertible Preferred Stock	Convertible preferred stock as of December 31, 2018 consisted of the following: Shares Shares Issued and Carrying Liquidation Authorized Outstanding Value Value Series A 60,000,000 24,000,000 $ 23,073,000 $ 24,000,000 Total 60,000,000 24,000,000 $ 23,073,000 $ 24,000,000

Common Stock (Tables)

Common Stock (Tables)	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Schedule of Common Stock Reserved for Issuance	Total common stock reserved for issuance is summarized as follows: As of December 31, 2019 2018 Series A convertible preferred stock outstanding, as converted — 3,860,383 Options issued and outstanding 1,320,243 591,448 Shares available for future option grants 1,523,950 472,714 Total common stock reserved for issuance 2,844,193 4,924,545

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Share-Based Compensation	The Company recorded share-based compensation for the periods indicated as follows (in thousands): Period from January 18, 2018 Year Ended (inception) to December 31, December 31, 2019 2018 Research and development $ 30 $ 13 General and administrative 359 95 Total share-based compensation $ 389 $ 108
Summary of Estimated Fair Value of Option Awards Granted Using Black-Scholes Option-Pricing Model	The fair value of option awards granted for the periods indicated was estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions: Period from January 18, 2018 Year Ended (inception) to December 31, December 31, 2019 2018 Expected term (years) 5.88-6.11 5.9 Expected volatility 61.8-87.6% 73.2 % Risk-free interest rate 1.6-2.6% 3.1 % Expected dividend — —
Summary of Stock Option Activity	The following table summarizes stock option activity under the 2019 Plan: Weighted Weighted Average Average Remaining Aggregate Number of Exercise Contractual Intrinsic Options Price Term Value (In years) (In thousands) Balance outstanding as of December 31, 2018 591,448 $ 1.93 9.87 $ — Granted 742,285 4.37 Exercised — — Cancelled (13,490 ) 1.93 Balance outstanding as of December 31, 2019 1,320,243 $ 3.34 9.23 $ 30,353 Exercisable as of December 31, 2019 235,188 $ 5,730

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Summary of Statutory Tax Rates Applicable to Income of Company and Subsidiaries	As a result of the Reorganization described in Note 1, as of December 31, 2019, the Company is taxed according to U.S. federal and state tax laws and Israeli tax laws. Prior to the Reorganization, for the year ended December 31, 2018, the Company was taxed according to Israeli tax laws. The statutory tax rates applicable to the income of the Company and its subsidiaries are as follows: Period from January 18, 2018 Year Ended (inception) to December 31, December 31, 2019 2018 89bio, Inc. 21 % — 89Bio Ltd 23 % 23 % 89bio Management, Inc. 21 % 21 % UAB 89bio Lithuania 15 % 15 %
Summary of Expense for Income Taxes	The expense for income Period from January 18, 2018 Year Ended (inception) to December 31, December 31, 2019 2018 Current: Federal $ 167 $ — State 1 — Foreign 30 48 Total 198 48 Deferred: Federal 20 — State — — Foreign — (20 ) Total 20 (20 ) Income tax expense $ 218 $ 28
Summary of Components of Deferred Tax Assets	Significant As of December 31, 2019 2018 Israel net operating loss carryforwards $ 4,328 $ 1,536 U.S. net operating loss carryforwards 1,916 — Research and development expenses 3,327 1,966 Other 451 20 Total deferred tax assets 10,022 3,522 Less: valuation allowance (10,022 ) (3,502 ) Net deferred tax assets $ — $ 20
Summary of Loss from Continuing Operations Before Taxes on Income	The Company recorded a loss from continuing operations, before taxes on income for the periods indicated as follows (in thousands): Period from January 18, 2018 Year Ended (inception) to December 31, December 31, 2019 2018 United States $ (19,502 ) $ 50 Lithuania 200 50 Israel (37,900 ) (16,248 ) Net loss before tax $ (57,202 ) $ (16,148 )
Summary of Reconciliation of Income Tax Expense Statutory Tax Rate to Effective Tax Rate	The reconciliation Period from January 18, 2018 Year Ended (inception) to December 31, December 31, 2019 2018 Income tax expense computed at statutory rates $ (13,095 ) $ (3,714 ) Change in valuation allowance 6,520 3,502 Change in Israel effective tax rate due to the 2019 reorganization 734 — Revaluation of convertible preferred share liability 6,039 226 Other 20 14 Income tax expense $ 218 $ 28

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2019
Earnings Per Share [Abstract]
Schedule of Outstanding Potentially Dilutive Securities Excluded From Calculation of Diluted Net Loss	The following outstanding potentially dilutive common stock equivalents have been excluded from the calculation of diluted net loss per share for the periods presented due to their anti-dilutive effect: Period from January 18, 2018 Year Ended (inception) to December 31, December 31, 2019 2018 Convertible preferred stock, as converted — 3,860,383 Stock options to purchase common stock 1,320,243 591,448 Shares available for future option grants 1,523,950 472,714 Total 2,844,193 4,924,545

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2019
Selected Quarterly Financial Information [Abstract]
Summary of Selected Quarterly Results From Operations	Selected quarterly results from operations for the year ended December 31, 2019 is as follows: Three Months Ended, December 31, September 30, June 30, March 31, (in thousands, except per share data) 2019 Loss from operations $ (9,611 ) $ (8,198 ) $ (3,947 ) $ (4,884 ) Net loss and comprehensive loss (19,283 ) (18,725 ) (14,525 ) (4,887 ) Net loss per share, basic and diluted $ (2.58 ) $ (30.63 ) $ (23.76 ) $ (8.00 ) Selected quarterly results from operations for the period from January 18, 2018 (inception) to December 31, 2018 is as follows: Period from January 18, 2018 Three Months Ended, (inception) to December 31, September 30, June 30, March 31, (in thousands, except per share data) 2018 Loss from operations $ (4,408 ) $ (3,786 ) $ (6,968 ) $ — Net loss and comprehensive loss (4,638 ) (4,165 ) (7,373 ) — Net loss per share, basic and diluted $ (7.59 ) $ (6.81 ) $ (13.55 ) $ —

Organization and Basis of Pre_2

Organization and Basis of Presentation - Additional Information (Details) $ / shares in Units, $ in Thousands	Nov. 13, 2019USD ($)$ / sharesshares	Oct. 24, 2019	Dec. 31, 2018USD ($)shares	Dec. 31, 2019USD ($)shares
Subsidiary Sale Of Stock [Line Items]
Date of incorporation				Jun. 28, 2019
Reorganization exchange of equity percentage of ordinary shares exchanged				100.00%
Reorganization exchange of equity percentage of common stock issued upon exchange				100.00%
Proceeds from issuance of common stock				$ 11
Reverse stock split conversion ratio	0.160849	0.160849
Reverse stock split, description		On October 24, 2019, 89bio, Inc.’s board of directors approved an amendment to the amended and restated certificate of incorporation of 89bio, Inc. to effect a 1 for 6.217 reverse split (“Reverse Split”) of shares of the common stock of 89bio, Inc. and a proportional adjustment to the conversion ratio of the convertible preferred stock, which was effected on October 25, 2019.
Reverse stock split date		Oct. 25, 2019
Cash and cash equivalents			$ 11,234	$ 93,335
Common Stock
Subsidiary Sale Of Stock [Line Items]
Shares issued and sold | shares			611,226
Convertible preferred stock automatically converted into common stock | shares	7,077,366
IPO | Common Stock
Subsidiary Sale Of Stock [Line Items]
Shares issued and sold | shares	6,100,390			6,100,390
IPO price per share | $ / shares	$ 16
Proceeds from issuance of common stock	$ 87,700
Payment of underwriting discounts, commissions	6,800
Other offering expenses	$ 3,100
Underwriters option | Common Stock
Subsidiary Sale Of Stock [Line Items]
Shares issued and sold | shares	795,703

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details)	Nov. 13, 2019USD ($)	Dec. 31, 2019USD ($)Segment	Dec. 31, 2018USD ($)
Summary Of Significant Accounting Policies [Line Items]
Expected dividend yield		0.00%
Deferred offering costs offset against IPO proceeds in additional paid-in capital	$ 3,100,000
Deferred offering costs			$ 0
Unrecognized tax benefits		$ 0	$ 0
Number of operating segments | Segment		1
Leasehold Improvements
Summary Of Significant Accounting Policies [Line Items]
Leasehold improvements amortization, description		Leasehold improvements are amortized on a straight-line basis over the shorter of the assets’ estimated useful life or the remaining term of the lease.
Minimum
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives		3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives		7 years

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Liabilities Measured at Fair Value on Recurring Basis (Details) - Recurring $ in Thousands	Dec. 31, 2018USD ($)
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial liabilities	$ 1,671
Convertible Preferred Stock Liability
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial liabilities	1,671
Level 3
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial liabilities	1,671
Level 3 | Convertible Preferred Stock Liability
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial liabilities	$ 1,671

Fair Value Measurements - Sum_2

Fair Value Measurements - Summary of Changes in Fair Value of Level 3 Liabilities (Details) - Recurring - Level 3 - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Fair Value Liabilities Measured on Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 1,671
Recognition of convertible preferred stock liability upon issuance of convertible preferred stock		$ 638
Revaluation of convertible preferred stock liability recorded in other expenses (income), net	30,597	979
Partial settlement of convertible preferred stock liability upon second closing		54
Partial settlement of convertible preferred stock liability upon third closing	(6,673)
Capital contribution related to extinguishment of preferred stock liability	$ (25,595)
Ending balance		$ 1,671

Fair Value Measurements - Sum_3

Fair Value Measurements - Summary of Fair Value Assumptions (Details) - Convertible Preferred Stock Liability - Black Scholes Option Pricing Model	11 Months Ended	12 Months Ended
	Dec. 31, 2018$ / shares	Dec. 31, 2019$ / shares
Stock Price | Minimum
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	0.96	0.99
Stock Price | Maximum
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	0.99	2.57
Exercise Price
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	1	1
Expected Term (Years) | Minimum
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	3 months	0 years
Expected Term (Years) | Maximum
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	3 years 2 months 15 days	2 years 3 months
Expected Volatility
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input		72
Expected Volatility | Minimum
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	70
Expected Volatility | Maximum
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	72
Risk-free Interest Rate | Minimum
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	2.1	0
Risk-free Interest Rate | Maximum
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	2.9	2.4

Consolidated Balance Sheet Co_3

Consolidated Balance Sheet Components - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Total property and equipment	$ 178	$ 39
Less: accumulated depreciation	(23)	(6)
Total property and equipment, net	155	33
Computer Software and Electronic Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	67	33
Furniture and Office Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	$ 111	$ 6

Consolidated Balance Sheet Co_4

Consolidated Balance Sheet Components - Additional Information (Details) - USD ($)	11 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Depreciation expense for property and equipment	$ 6,000	$ 17,000

Consolidated Balance Sheet Co_5

Consolidated Balance Sheet Components - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Accrued research and development expenses	$ 2,326	$ 890
Accrued employee and related expenses	1,396	283
Accrued professional and legal fees	573
Accrued other	325
Total accrued expenses	$ 4,620	$ 1,173

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($)	1 Months Ended			11 Months Ended	12 Months Ended
	Dec. 31, 2019	May 31, 2018	Apr. 30, 2018	Dec. 31, 2018	Dec. 31, 2019
Loss Contingencies [Line Items]
Lessee, operating lease, description	The lease term is for 24 months, expiring in January 2022	The lease term was for 12 months and was amended in April 2019 to extend the lease term to April 2020.
Operating lease, payments	$ 17,500	$ 4,000
Lessee, operating lease term of contract	24 months	12 months			24 months
Operating leases, rent expense				$ 39,000	$ 159,000
Teva Agreements
Loss Contingencies [Line Items]
Nonrefundable upfront payment			$ 6,000,000
Payment upon achievement of certain clinical and commercial milestones			135,000,000
Asset transfer and license agreement, termination period after written notice					120 days
Asset transfer and license agreement, termination period notice of breach					60 days
Asset transfer and license agreement termination notice period if bankruptcy petition filed					60 days
Teva Agreements | Research and Development Expenses
Loss Contingencies [Line Items]
Up-front license payment				6,000,000	$ 0
Teva Agreements | Teva’s GlycoPEGylated FGF21 Program
Loss Contingencies [Line Items]
Payment upon achievement of certain clinical and commercial milestones			67,500,000
Teva Agreements | Teva’s Development Program
Loss Contingencies [Line Items]
Payment upon achievement of certain clinical and commercial milestones			$ 67,500,000
Restricted Cash And Other Assets Member
Loss Contingencies [Line Items]
Security deposit	$ 95,000			$ 23,000	$ 95,000

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under Non-cancellable Operating Lease Obligations (Details) $ in Thousands	Dec. 31, 2019USD ($)
Commitments And Contingencies Disclosure [Abstract]
2020	$ 226
2021	216
Total future minimum annual payments	$ 442

Convertible Note - Additional I

Convertible Note - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Apr. 30, 2018	Dec. 31, 2019	Mar. 31, 2018
Convertible Note
Debt Instrument [Line Items]
Debt instrument, principal amount			$ 100,000
Fixed interest rate per annum			8.00%
Series A Convertible Preferred Stock
Debt Instrument [Line Items]
Convertible note outstanding amount converted into shares	100,000
Convertible note, conversion description		the entire amount outstanding converted into 100,000 shares of Series A convertible preferred stock upon the initial closing of the Series A financing

Convertible Preferred Stock - A

Convertible Preferred Stock - Additional Information (Details) - USD ($)	Nov. 13, 2019	Apr. 16, 2018	Jul. 31, 2019	Jun. 30, 2019	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2019	Apr. 30, 2018
Temporary Equity [Line Items]
Per share price of issuance of shares					$ 0.001	$ 0.001	$ 0.001
Shares issued					24,000,000	24,000,000	0
Net cash proceeds						$ 23,665,000	$ 20,000,000
Capital contribution related to extinguishment of preferred stock liability	$ 25,600,000						$ 25,595,000
Convertible preferred stock outstanding					24,000,000	24,000,000	0
Common Stock
Temporary Equity [Line Items]
Capital contribution related to extinguishment of preferred stock liability							$ 0
Convertible preferred stock automatically converted into common stock	7,077,366
Series A Convertible Preferred Stock
Temporary Equity [Line Items]
Number of shares committed to purchase, no longer issuable	16,000,000
Convertible preferred stock, liquidation preference per share							$ 1
Series A Share Purchase Agreement | Series A Convertible Preferred Stock
Temporary Equity [Line Items]
Per share price of issuance of shares								$ 1
Net cash proceeds			$ 20,000,000	$ 20,000,000
Net value of commitment to purchase and sell shares		$ 638,000
Series A Share Purchase Agreement | Series A Convertible Preferred Stock | Other Expenses (Income), Net
Temporary Equity [Line Items]
Expense recorded for revaluation of convertible preferred stock liability						$ 1,000,000	$ 30,600,000
Series A Share Purchase Agreement | Series A Convertible Preferred Stock | Initial Closing
Temporary Equity [Line Items]
Per share price of issuance of shares		$ 1
Shares issued		14,900,000
Net cash proceeds		$ 14,700,000
Series A Share Purchase Agreement | Series A Convertible Preferred Stock | Second Closing
Temporary Equity [Line Items]
Per share price of issuance of shares		$ 1		$ 1	$ 1	$ 1
Shares issued					9,000,000	9,000,000
Net cash proceeds					$ 9,000,000
Number of shares committed to purchase		15,000,000
Remaining shares issued				6,000,000
Series A Share Purchase Agreement | Series A Convertible Preferred Stock | Third Closing
Temporary Equity [Line Items]
Per share price of issuance of shares		$ 1		$ 1
Shares issued				14,000,000
Number of shares committed to purchase		30,000,000
Series A Share Purchase Agreement | Series A Convertible Preferred Stock | Maximum
Temporary Equity [Line Items]
Total amount of preferred shares issuable by the entity								$ 60,000,000

Convertible Preferred Stock - S

Convertible Preferred Stock - Schedule of Convertible Preferred Stock (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Temporary Equity [Line Items]
Convertible preferred stock, shares authorized	0	60,000,000
Convertible preferred stock, issued and outstanding		24,000,000
Convertible preferred stock, carrying value		$ 23,073,000
Convertible preferred stock, liquidation value	$ 0	$ 24,000,000
Series A Convertible Preferred Stock
Temporary Equity [Line Items]
Convertible preferred stock, shares authorized		60,000,000
Convertible preferred stock, issued and outstanding		24,000,000
Convertible preferred stock, carrying value		$ 23,073,000
Convertible preferred stock, liquidation value		$ 24,000,000

Common Stock - Additional Infor

Common Stock - Additional Information (Details) - $ / shares	Dec. 31, 2019	Oct. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Common stock, shares outstanding	13,788,982	13,788,982	611,226
Common stock, shares authorized	100,000,000	100,000,000	10,415,900
Common stock, par value	$ 0.001	$ 0.001	$ 0.001
Common stock, shares issued	13,788,982	13,788,982	611,226

Common Stock - Schedule of Comm

Common Stock - Schedule of Common Stock Reserved for Issuance (Details) - shares	Dec. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Total common stock reserved for issuance	2,844,193	4,924,545
Series A Convertible Preferred Stock Outstanding Reserved for Issuance
Class Of Stock [Line Items]
Total common stock reserved for issuance		3,860,383
Options Issued and Outstanding Reserved for Issuance
Class Of Stock [Line Items]
Total common stock reserved for issuance	1,320,243	591,448
Shares Available for Future Option Grants Reserved for Issuance
Class Of Stock [Line Items]
Total common stock reserved for issuance	1,523,950	472,714

Share-Based Compensation - Addi

Share-Based Compensation - Additional Information (Details) - USD ($)	1 Months Ended	11 Months Ended	12 Months Ended
	Oct. 31, 2019	Dec. 31, 2018	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total common stock reserved for issuance		4,924,545	2,844,193
Non-employee
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted			3,216
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common shares issuable under the plan (in shares)	225,188
Percentage of increase in number of shares of capital stock issued and outstanding	1.00%
Percent of purchase shares of common stock	85.00%
Number of shares of common stock remained available for issuance under ESPP			225,188
2019 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common shares issuable under the plan (in shares)			2,844,193
Percentage of increase in number of shares of capital stock issued and outstanding			4.00%
Total common stock reserved for issuance			1,523,950
Vesting period			4 years
Percentage of option vesting			25.00%
Terms of award			The Board determines the period over which options become exercisable and options generally vest over a four-year period, with 25% of options vesting on the first anniversary of employment, and thereafter, the remaining options vesting quarterly, over the following 36-month period. The options will expire within ten years from the date of grant.
Remaining option vesting period			36 months
Expiration period			10 years
Estimated total grant date fair value of options vested			$ 296,000
Weighted average fair value options granted			$ 2.90
Unrecognized stock option granted under plan			$ 2,400
Unrecognized weighted average period			3 years 4 months 24 days
Stock options granted			742,285
2018 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vested		0
Weighted average fair value options granted		$ 1.31
Maximum | Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Period for increase in number of shares of common stock reserved for issuance	10 years
Maximum | 2019 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Period for increase in number of shares of common stock reserved for issuance			10 years

Share-Based Compensation - Summ

Share-Based Compensation - Summary of Share-Based Compensation (Details) - USD ($) $ in Thousands	11 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation	$ 108	$ 389
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation	13	30
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation	$ 95	$ 359

Share-Based Compensation - Su_2

Share-Based Compensation - Summary of Estimated Fair Value of Option Awards Granted Using Black-Scholes Option-Pricing Model (Details)	11 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	5 years 10 months 24 days
Expected volatility, minimum		61.80%
Expected volatility, maximum		87.60%
Risk-free interest rate, minimum		1.60%
Risk-free interest rate, maximum		2.60%
Expected dividend yield		0.00%
Expected volatility	73.20%
Risk-free interest rate	3.10%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)		5 years 10 months 17 days
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)		6 years 1 month 9 days

Share-Based Compensation - Su_3

Share-Based Compensation - Summary of Stock Option Activity (Details) - 2019 Plan - USD ($) $ / shares in Units, $ in Thousands	11 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019
Number of Options
Outstanding, Beginning Balance		591,448
Granted		742,285
Cancelled		(13,490)
Outstanding, Ending Balance	591,448	1,320,243
Exercisable as of December 31, 2019		235,188
Weighted Average Exercise Price
Weighted Average Exercise Price Outstanding, Beginning Balance		$ 1.93
Weighted Average Exercise Price, Granted		4.37
Weighted Average Exercise Price, Cancelled		1.93
Weighted Average Exercise Price Outstanding, Ending Balance	$ 1.93	$ 3.34
Weighted Average Remaining Contractual Term (In years)
Weighted Average Remaining Contractual Term (In years), Outstanding	9 years 10 months 13 days	9 years 2 months 23 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value Outstanding		$ 30,353
Aggregate Intrinsic Value, Exercisable as of December 31, 2019		$ 5,730

Income Taxes - Summary of Statu

Income Taxes - Summary of Statutory Tax Rates Applicable to Income of Company and Subsidiaries (Details)	11 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019
Income Tax Disclosure [Line Items]
Effective income tax rate		21.00%
89Bio Ltd
Income Tax Disclosure [Line Items]
Effective income tax rate	23.00%	23.00%
89bio Management, Inc.
Income Tax Disclosure [Line Items]
Effective income tax rate	21.00%	21.00%
UAB 89bio Lithuania
Income Tax Disclosure [Line Items]
Effective income tax rate	15.00%	15.00%

Income Taxes - Summary of Expen

Income Taxes - Summary of Expense for Income Taxes (Details) - USD ($) $ in Thousands	11 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019
Current:
Federal		$ 167
State		1
Foreign	$ 48	30
Total	48	198
Deferred:
Federal		20
Foreign	(20)
Total	(20)	20
Income tax expense	$ 28	$ 218

Income Taxes - Summary of Compo

Income Taxes - Summary of Components of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Line Items]
Research and development expenses	$ 3,327	$ 1,966
Other	451	20
Total deferred tax assets	10,022	3,522
Less: valuation allowance	(10,022)	(3,502)
Net deferred tax assets		20
Israel
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	4,328	$ 1,536
United States
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 1,916

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Line Items]
Deferred tax assets, valuation allowance	$ 10,022,000	$ 3,502,000
Deferred tax assets, increase in valuation allowance	$ 6,500,000
Operating loss carryforwards limitations on use	Federal net operating losses generated after 2017 can be carried forward indefinitely but utilization will be limited to 80% of taxable income in the period that net operating losses are being utilized.
Taxable income utilization percentage	80.00%
State research and development credit carryforwards	$ 156,000
Unrecognized tax benefits	0	0
Increase in unrecognized tax benefits	39,000
United States
Income Tax Disclosure [Line Items]
Deferred tax assets, increase in valuation allowance	20,000
Accumulated tax loss carryforward	9,100,000
Israeli
Income Tax Disclosure [Line Items]
Accumulated tax loss carryforward	$ 23,800,000	$ 6,700,000

Income Taxes - Summary of Loss

Income Taxes - Summary of Loss from Continuing Operations Before Taxes on Income (Details) - USD ($) $ in Thousands	11 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019
Income Tax Disclosure [Line Items]
Net loss before tax	$ (16,148)	$ (57,202)
United States
Income Tax Disclosure [Line Items]
Net loss before tax	50	(19,502)
Lithuania
Income Tax Disclosure [Line Items]
Net loss before tax	50	200
Israel
Income Tax Disclosure [Line Items]
Net loss before tax	$ (16,248)	$ (37,900)

Income Taxes - Summary of Recon

Income Taxes - Summary of Reconciliation of Income Tax Expense Statutory Tax Rate to Effective Tax Rate (Details) - USD ($) $ in Thousands	11 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income tax expense computed at statutory rates	$ (3,714)	$ (13,095)
Change in valuation allowance	3,502	6,520
Change in Israel effective tax rate due to the 2019 reorganization		734
Revaluation of convertible preferred share liability	226	6,039
Other	14	20
Income tax expense	$ 28	$ 218

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Outstanding Potentially Dilutive Securities Excluded From Calculation of Diluted Net Loss (Details) - shares	11 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	4,924,545	2,844,193
Convertible Preferred Stock, as Converted
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	3,860,383
Stock Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	591,448	1,320,243
Shares Available for Future Option Grants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	472,714	1,523,950

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - USD ($)	Nov. 13, 2019	Dec. 31, 2018	Dec. 31, 2019
Related Party Transaction [Line Items]
Outstanding liability to related party		$ 23,000	$ 11,000
Capital contribution	$ 25,600,000		25,595,000
Series A Convertible Preferred Stock
Related Party Transaction [Line Items]
Number of shares committed to purchase, no longer issuable	16,000,000
Additional Paid-in Capital
Related Party Transaction [Line Items]
Capital contribution			25,595,000
Board of Directors
Related Party Transaction [Line Items]
Professional services expense		$ 147,000	$ 170,000

Selected Quarterly Financial _3

Selected Quarterly Financial Data - Summary of Selected Quarterly Results From Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended							11 Months Ended		12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2019
Selected Quarterly Financial Information [Abstract]
Loss from operations	$ (9,611)	$ (8,198)	$ (3,947)	$ (4,884)	$ (4,408)	$ (3,786)	$ (6,968)	$ (15,162)		$ (26,640)
Net loss and comprehensive loss	$ (19,283)	$ (18,725)	$ (14,525)	$ (4,887)	$ (4,638)	$ (4,165)	$ (7,373)	$ (16,176)	$ (16,176)	$ (57,420)
Net loss per share, basic and diluted	$ (2.58)	$ (30.63)	$ (23.76)	$ (8)	$ (7.59)	$ (6.81)	$ (13.55)	$ 36.45		$ 24.49