89bio (ETNB) 10-K 25 Mar 21 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Mar. 01, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
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			$ 72,707,052
Entity Common Stock, Shares Outstanding		19,946,426
ICFR Auditor Attestation Flag	false
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
Documents Incorporated by Reference	Portions of the registrant’s definitive proxy statement relating to its 2021 Annual Meeting of Stockholders, to be held on or about June 2, 2021, are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated. Such proxy statement will be filed with the U.S. Securities and Exchange Commission within 120 days after the end of the fiscal year to which this report relates.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 98,183	$ 93,335
Restricted cash	25	25
Short-term investments	106,446
Prepaid and other current assets	5,548	1,966
Total current assets	210,202	95,326
Property and equipment, net	166	155
Other assets	706	72
Total assets	211,074	95,553
Current liabilities:
Accounts payable	2,065	989
Accrued expenses	6,048	4,620
Total current liabilities	8,113	5,609
Commitments and contingencies (Note 5)
Stockholders’ equity:
Common stock, $0.001 par value, 100,000,000 shares authorized as of December 31, 2020 and 2019, respectively; 19,931,660 and 13,788,982 shares issued and outstanding as of December 31, 2020 and 2019, respectively	20	14
Additional paid-in capital	326,046	163,526
Accumulated other comprehensive loss	(10)
Accumulated deficit	(123,095)	(73,596)
Total stockholders’ equity	202,961	89,944
Total liabilities and stockholders’ equity	$ 211,074	$ 95,553

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	19,931,660	13,788,982
Common stock, shares outstanding	19,931,660	13,788,982

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Operating expenses:
Research and development	$ 36,199	$ 21,346
General and administrative	13,156	5,294
Total operating expenses	49,355	26,640
Loss from operations	(49,355)	(26,640)
Other expenses, net	(203)	(30,562)
Net loss before income tax	(49,558)	(57,202)
Income tax benefit (expense)	59	(218)
Net loss	(49,499)	(57,420)
Other comprehensive income (loss):
Unrealized gain on available-for-sale securities	8
Foreign currency translation adjustments	(18)
Total other comprehensive loss	(10)
Comprehensive loss	$ (49,509)	$ (57,420)
Net loss per share, basic and diluted	$ (3.08)	$ (24.49)
Weighted-average shares used to compute net loss per share, basic and diluted	16,087,785	2,344,191

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Public Offerings	Common Stock	Common StockPublic Offerings	Additional Paid-in Capital	Additional Paid-in CapitalPublic Offerings	Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive LossPublic Offerings	Retained Earnings	Convertible Preferred Stock
Beginning balance at Dec. 31, 2018	$ (16,057)		$ 1		$ 118		$ 0		$ (16,176)
Beginning balance, shares at Dec. 31, 2018										24,000,000
Beginning balance at Dec. 31, 2018										$ 23,073
Beginning balance, shares at Dec. 31, 2018			611,226
Issuance of convertible preferred stock, net of issuance costs							0			$ 26,673
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		$ 7		49,739		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)
Conversion of convertible preferred stock into common stock upon completion of initial public offering, shares			7,077,366
Issuance of common stock		$ 87,691		$ 6		$ 87,685		$ 0
Issuance of common stock, shares				6,100,390
Capital contribution related to extinguishment of convertible preferred stock liability	25,595				25,595		0
Share-based compensation	389				389		0
Net loss	(57,420)						0		(57,420)
Ending balance at Dec. 31, 2019	$ 89,944		$ 14		163,526		0		(73,596)
Ending balance, shares at Dec. 31, 2019	0
Ending balance, shares at Dec. 31, 2019			13,788,982
Issuance of common stock		$ 157,680		$ 6		$ 157,674		$ 0
Issuance of common stock, shares				6,072,040
Issuance of common stock upon exercise of stock options	$ 271				271		0
Issuance of common stock upon exercise of stock options, shares			63,366
Stock Issued During Period Value Employee Stock Purchase Plan	134				134		0
Issuance of common stock upon ESPP purchase, Shares			7,272
Issuance Of Common Stock Warrants In Connection With Debt Financing	634				634		0
Share-based compensation	3,807				3,807		0
Net loss	(49,499)						0		(49,499)
Other comprehensive loss	(10)						(10)
Ending balance at Dec. 31, 2020	$ 202,961		$ 20		$ 326,046		$ (10)		$ (123,095)
Ending balance, shares at Dec. 31, 2020	0
Ending balance, shares at Dec. 31, 2020			19,931,660

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Stock issuance costs		$ 3,083
Convertible Preferred Shares
Temporary equity, issuance costs	$ 1,208	0
Temporary equity, settlement of convertible preferred stock liability		$ 6,673

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net loss	$ (49,499,000)	$ (57,420,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	60,000	17,000
Share-based compensation	3,807,000	389,000
Deferred tax assets	(69,000)	20,000
Revaluation of convertible preferred stock liability		30,597,000
Amortization of premium on available-for-sale securities	268,000
Amortization of debt issuance costs	230,000
Changes in operating assets and liabilities:
Prepaids and other current assets	(3,600,000)	(1,918,000)
Other assets		(72,000)
Accounts payable	1,131,000	(520,000)
Accrued expenses	1,428,000	3,447,000
Net cash used in operating activities	(46,244,000)	(25,460,000)
Cash flows from investing activities:
Purchases of available-for-sale securities	(118,895,000)
Proceeds from maturities of available-for-sale securities	12,189,000
Purchases of property and equipment	(126,000)	(139,000)
Net cash used in investing activities	(106,832,000)	(139,000)
Cash flows from financing activities:
Proceeds from issuance of common stock upon public offerings, net of issuance costs	157,680,000
Proceeds from issuance of common stock upon initial public offering, net of issuance costs		87,691,000
Proceeds from issuance of convertible preferred stock and convertible preferred stock liability, net of issuance costs		20,000,000
Proceeds from issuance of common stock upon stock option exercises	271,000
Proceeds from issuance of common stock		11,000
Payment of debt issuance costs	(161,000)
Net cash provided by financing activities	157,924,000	107,702,000
Net increase in cash and cash equivalents, and restricted cash	4,848,000	82,103,000
Cash and cash equivalents, and restricted cash at beginning of period	93,360,000	11,257,000
Cash and cash equivalents, and restricted cash at end of period	98,208,000	93,360,000
Components of cash and cash equivalents, and restricted cash:
Cash and cash equivalents	98,183,000	93,335,000
Restricted cash	25,000	25,000
Cash and cash equivalents, and restricted cash at end of period	98,208,000	93,360,000
Supplemental disclosures of noncash information:
Issuance of common stock warrant in connection with term loan facility	634,000
Property and equipment purchases included in accounts payable		55,000
Cash paid for taxes	142,000	106,000
Conversion of convertible preferred stock into common stock at close of initial public offering		49,746,000
Capital contribution related to extinguishment of convertible preferred stock liability		$ 25,595,000
ESPP Purchases
Cash flows from financing activities:
Proceeds from issuance of common stock	$ 134,000

Organization and Basis of Prese

Organization and Basis of Presentation	12 Months Ended
	Dec. 31, 2020
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 and for the treatment of severe hypertriglyceridemia. 89bio, Inc. was formed as a Delaware corporation in June 2019, for the purpose of completing an initial public offering (“IPO”) and related transactions in order to carry on the business of 89Bio Ltd., which was incorporated in Israel in January 2018. 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. Public Offerings In November 2019, 89bio, Inc. completed its 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. In July 2020, the Company completed an underwritten public offering of 3,047,040 shares of its common stock (inclusive of 397,440 shares pursuant to the underwriters’ option to purchase additional shares), at the public offering price of $27.50 per share. The Company raised a total of $83.8 million in gross proceeds from the offering, or approximately $78.2 million in net proceeds after deducting underwriting discounts and commissions of $5.0 million and offering costs of approximately $0.6 million. In September 2020, the Company completed an underwritten public offering of 3,025,000 shares of its common stock, at a public offering price of $28.00 per share. The Company raised a total of $84.7 million in gross proceeds from the offering, or approximately $79.5 million in net proceeds after deducting underwriting discounts and commissions of $4.6 million and offering costs of approximately $0.6 million. 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, cash equivalents and short-term investments of $204.6 million as of December 31, 2020. The Company expects that its cash, cash equivalents and short-term investments as of December 31, 2020, together with proceeds available from the Company’s term loan (see Note 6), 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, 2020
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. Reclassification Certain prior year footnote amounts have been updated for consistency with the current year presentation. Such reclassification has no effect on the consolidated financial statements. Foreign Currencies Certain transactions during the years ended December 31, 2020 and 2019 were denominated in currencies other than the U.S. dollar. Gains and losses from foreign currency transactions were not material for all periods presented and are reflected in the consolidated statements of operations and comprehensive loss as a component of other expenses, net. The Company’s subsidiary in Lithuania uses the Euro as its functional currency for financial reporting. The re-measurement from Euros to U.S. dollars results in translation gain and loss adjustments, which are reflected as a component of comprehensive loss as foreign currency translation adjustments. 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 and certain accrued expenses. 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. 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. The ongoing COVID-19 pandemic has disrupted and may continue to disrupt the Company’s business and delay its preclinical and clinical programs and timelines. The Company does not yet know the full extent of potential delays to clinical trials, which could prevent or delay the Company from obtaining approval for BIO89-100. Segment Reporting The Company has one operating Cash and Cash Equivalents 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 funds and commercial paper that are stated at fair value. Restricted Cash Restricted cash consists of a money market account that serves as collateral for the Company’s operating lease agreement for its facility in Israel. Investments Investments have been classified as available-for-sale and are carried at estimated fair value as determined based upon quoted market prices or pricing models for similar securities. Management determines the appropriate classification of its investments in debt securities at the time of purchase. Generally, investments with original maturities beyond three months at the date of purchase are classified as short-term because it is management’s intent to use the investments to fund current operations or to make them available for current operations. Unrealized gains and losses are excluded from earnings and are reported as a component of comprehensive loss. The Company periodically evaluates whether declines in fair values of its available-for-sale securities below their book value are other-than-temporary. This evaluation consists of several qualitative and quantitative factors regarding the severity and duration of the unrealized loss as well as the Company’s ability and intent to hold the available-for-sale security until a forecasted recovery occurs. Additionally, the Company assesses whether it has plans to sell the security or it is more likely than not it will be required to sell any available-for-sale securities before recovery of its amortized cost basis. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on available-for-sale securities are included in other expenses, net. The cost of investments sold is based on the specific-identification method. There are no material realized gains or losses on investments for the periods presented. Interest on available-for-sale securities is included in other expenses, net and is not material for all periods presented. Property Property Upon retirement or sale of the assets, the cost and related accumulated depreciation and amortization are removed from the consolidated balance sheets and the resulting gains or losses are recorded in the consolidated statements of operations and comprehensive loss. Impairment The Company periodically Accrued Research and Development Expenses The Company estimates preclinical The Company accrues for these Leases The Company leases 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 Research and Research Share-Based Compensation The Company measures The Company estimates The Black-Scholes • Expected volatility—Since the Company has limited trading history for its common stock due to its short trading history, the expected volatility is estimated based on the volatility of comparable publicly traded biotechnology companies during the equivalent period of the calculated expected term of the options granted. The comparable companies were chosen based on their similar size, stage in the life cycle or area of specialty. • Expected term—The expected term of options granted to employees and directors is determined using the “simplified” method. Under this approach, the expected term is presumed to be the midpoint between the weighted-average vesting term and the contractual term of the option. The simplified method makes the assumption that the employee will exercise share options evenly over the period when the share options are vested and ending on the date when the share options would expire. The expected option term for options granted to non-employees is estimated on a grant-by-grant basis. • Risk-free interest rate—The risk-free interest rate is based on the U.S. Treasury zero coupon bonds in effect on the grant date for periods with an equivalent expected term as the option. • Expected dividend—The Company has never paid dividends and has no foreseeable plans to pay dividends on its shares of common stock. Therefore, an expected dividend of zero is used. Income Taxes Income Basic and Basic loss per share Comprehensive The Company’s comprehensive loss is comprised of changes in unrealized gains or losses on available-for-sale securities and foreign currency translation adjustments. Recently Adopted Accounting Standards In August 2018, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) No. 2018-13, Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement Recent Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02— Leases

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The following table presents the Company’s financial assets measured at fair value on a recurring basis by level within the fair value hierarchy as of December 31, 2020 (in thousands): As of December 31, 2020 Valuation Amortized Unrealized Unrealized Hierarchy Cost Gains Losses Fair Value Money market funds Level 1 $ 46,134 $ — $ — $ 46,134 Commercial paper Level 2 76,605 — (2 ) 76,603 Agency bonds Level 2 29,654 15 — 29,669 Corporate debt securities Level 2 11,890 — (6 ) 11,884 U.S. government bonds Level 2 7,093 — — 7,093 Municipal bonds Level 2 5,592 2 (1 ) 5,593 U.S. treasury bills Level 2 4,680 — — 4,680 Agency discount securities Level 2 200 — — 200 Total cash equivalents and available-for-sale securities $ 181,848 $ 17 $ (9 ) $ 181,856 Classified as: Cash equivalents $ 75,410 Short-term investments 106,446 Total cash equivalents and available-for-sale securities $ 181,856 The following table summarizes the Company’s cash equivalents and available-for-sale securities by contractual maturity as of December 31, 2020 (in thousands): As of December 31, 2020 Within one year $ 160,304 After one year through two years 21,552 Total cash equivalents and available-for-sale securities $ 181,856 The Company did not hold any financial assets as of December 31, 2019. The Company’s convertible preferred stock liability represented a Level 3 financial liability measured at fair value on a recurring basis prior to its extinguishment in the fourth quarter of 2019. Accordingly, there was no Level 3 financial liability outstanding during the year ended and as of December 31, 2020. For the year ended December 31, 2019, changes in the fair value of the Company’s Level 3 financial liability measured on a recurring basis were as follows (in thousands): Year Ended December 31, 2019 Beginning balance $ 1,671 Revaluation of convertible preferred stock liability recorded in other expenses (income), net 30,597 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 $ — 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: Year Ended December 31, 2019 Stock price $0.99-$2.57 Exercise price $1.00 Expected term (years) 0.00-2.25 Expected volatility 72.0 % Risk-free interest rate 0.0-2.4%

Consolidated Balance Sheet Comp

Consolidated Balance Sheet Components	12 Months Ended
	Dec. 31, 2020
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, 2020 2019 Computer equipment $ 105 $ 67 Furniture and office equipment 144 111 Total property and equipment 249 178 Less: accumulated depreciation (83 ) (23 ) Total property and equipment, net $ 166 $ 155 Depreciation expense for property and equipment was $60,000 and $17,000 for the years ended December 31, 2020 and 2019, respectively. Accrued Expenses Accrued expenses consist of the following (in thousands): As of December 31, 2020 2019 Accrued research and development expenses $ 2,884 $ 2,326 Accrued employee and related expenses 2,552 1,396 Accrued professional and legal fees 453 573 Accrued other 159 325 Total accrued expenses $ 6,048 $ 4,620

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
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 during 2020 were approximately $17,500. Future minimum As of December 31, 2020 2021 $ 232 2022 8 Total future minimum annual payments $ 240 Rent expense was $273,000 and $159,000 for years ended December 31, 2020 and 2019, respectively. 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, 2020 and 2019. 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. During the years ended December 31, 2020 and 2019, there were no license payment expenses related to the Teva Agreements.

Term Loan

Term Loan	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Term Loan	6. Term Loan Loan and Security Agreement In April 2020, the Company and certain of its subsidiaries entered into a Loan and Security Agreement (the “Loan Agreement”) with the lenders referred to therein (the “Lenders”), and Silicon Valley Bank, as collateral agent. The Loan Agreement provides for (i) a secured term A loan facility (the “Term A Loan Facility”) of up to $10.0 million and (ii) a secured term B loan facility (the “Term B Loan Facility”) of up to $5.0 million that is available upon the Company satisfying certain milestones. The Term A Loan Facility matures on November 1, 2022, provided, that if the Term B Loan Facility is funded, the facilities instead mature on September 1, 2023. The loans will bear interest at the greater of (i) 4.50% and (ii) the sum of (a) the Prime Rate as reported in The Wall Street Journal plus (b) 1.25%. As of December 31, 2020, the Company had not drawn any amount under the Loan Agreement. In connection with the execution of the Loan Agreement, the Company agreed to issue the Lenders warrants to purchase shares of the Company’s common stock. In April 2020, the Company issued Silicon Valley Bank a warrant to purchase 25,000 shares of the Company’s common stock with a warrant exercise price of $22.06 per share that is immediately exercisable. The initial expiration date of April 7, 2030 was changed to June 30, 2025 in connection with the July 2020 offering. The Company determined the fair value of the warrant at the issuance date by using the Black-Scholes option-pricing model with the following assumptions: risk-free interest rate of 0.75%, no dividends, expected volatility of 92.3% and expected term of 10.0 years. Upon issuance, the fair value allocated to the warrant of $0.6 million was recorded as a debt issuance cost and classified within other assets and met the requirements for equity classification within additional paid-in capital on the consolidated balance sheets. An additional warrant to purchase 8,333 shares of the Company’s common stock will be issued in connection with the Term B Loan Facility, if funded, with the exercise price determined on the Company’s stock price at the time of issuance. Additionally, the Company incurred $0.2 million in closing costs that were recorded as debt issuance costs and classified within other assets on the consolidated balance sheets. The deferred assets related to the debt issuance cost and warrant are recognized as interest expense over the duration of the Loan Agreement and are recorded within other expenses, net on the consolidated statements of operations and comprehensive loss. As of December 31, 2020, the remaining unamortized debt issuance costs classified within other assets on the consolidated balance sheet is $0.6 million.

Convertible Preferred Stock

Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2020
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 in subsequent closings. Upon the completion of the Company’s IPO on November 13, 2019, there were 16,000,000 remaining shares of convertible preferred stock that were previously issuable that 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 during 2019. 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.

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share-Based Compensation	8. 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 in September 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, 2020, there were 1,433,991 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. Employee Stock Purchase Plan 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 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 and each offering is expected to be 6 months long. For each offering period, ESPP participants will purchase shares of common stock at a price per share equal to 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 the applicable offering period The first six-month offering period under the ESPP commenced on January 1, 2020 and ended on June 30, 2020 and the second six-month offering period commenced on July 1, 2020 and ended on December 31, 2020. A total of 7,272 shares of common stock were purchased pursuant to the ESPP for the year ended December 31, 2020. The Company recorded share-based compensation for the periods indicated as follows (in thousands): Year Ended December 31, 2020 2019 Research and development $ 1,250 $ 30 General and administrative 2,557 359 Total share-based compensation $ 3,807 $ 389 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: Year Ended December 31, 2020 2019 Expected term (years) 4.0-6.1 5.9-6.1 Contractual term (years) 10.0 10.0 Expected volatility 86.4-97.6% 61.8-87.6% Risk-free interest rate 0.2-1.5% 1.6-2.6% Expected dividend — — The following table summarizes stock option activity for the year ended December 31, 2020: 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, 2019 1,320,243 $ 3.34 9.23 $ 30,353 Granted 682,000 29.78 Exercised (63,366 ) 4.29 Cancelled (40,482 ) 2.87 Balance outstanding as of December 31, 2020 1,898,395 12.79 8.60 $ 25,918 Exercisable as of December 31, 2020 535,084 $ 2.58 8.11 $ 11,684 During the year ended December 31, 2020, the estimated total grant date fair value of options vested was $0.8 million. The weighted-average

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes Tax Rates Applicable to the Income of the Company and its Subsidiaries As a result of the Reorganization described in Note 1, the Company is taxed according to U.S. federal and state tax laws and Israeli tax laws. The statutory tax rates applicable to the income of the Company and its subsidiaries are as follows: Year Ended December 31, 2020 2019 89bio, Inc. 21 % 21 % 89Bio Ltd 23 % 23 % 89bio Management, Inc. 21 % 21 % UAB 89bio Lithuania 15 % 15 % The income Year Ended December 31, 2020 2019 Current: Federal $ (11 ) $ (167 ) State 1 (1 ) Foreign — (30 ) Total (10 ) (198 ) Deferred: Federal 69 (20 ) Total 69 (20 ) Income tax benefit (expense) $ 59 $ (218 ) Deferred Deferred As of December 31, 2020 2019 U.S. net operating loss carryforwards $ 11,342 $ 1,916 Israel net operating loss carryforwards 3,978 4,328 Research and development expenses 5,392 3,419 Accrued expenses 635 349 Other 658 10 Total deferred tax assets 22,005 10,022 Less: valuation allowance (21,936 ) (10,022 ) Net deferred tax assets $ 69 $ — U.S. research and development expenses and accrued expenses disclosed for the year ended December 31, 2019 were previously reported in the 2019 notes to the consolidated financial statements as a component of other. The reclassification had no impact on the consolidated financial statements for the year ended December 31, 2019. As Available Losses and Credits As of December 31, 2020, the Company has an accumulated As of December 31, 2020, the Company has federal research and development credit carryforwards of approximately $0.6 million, which expire beginning in 2040. As of December 31, 2020 and 2019, the Company has state research and development credit carryforwards of approximately $0.7 million and $0.2 million, respectively, which will carry forward indefinitely. Loss from Continuing Operations, Before Income Tax The Company recorded a loss from continuing operations, before income tax for the periods indicated as follows (in thousands): Year Ended December 31, 2020 2019 United States $ (58,760 ) $ (19,502 ) Lithuania (73 ) 200 Israel 9,275 (37,900 ) Net loss before income tax $ (49,558 ) $ (57,202 ) Reconciliation of Income Tax Benefit (Expense) The reconciliation Year Ended December 31, 2020 2019 Income tax benefit computed at statutory rates $ 8,285 $ 13,095 Research and development credits, net of uncertain tax position 815 93 Change in valuation allowance (11,914 ) (6,520 ) Change in Israel effective tax rate due to the 2019 reorganization 647 (734 ) Foreign rate differential 1,671 — Revaluation of convertible preferred stock liability — (6,039 ) Other 555 (113 ) Income tax benefit (expense) $ 59 $ (218 ) Research and development credits, net of uncertain tax position disclosed for the year ended December 31, 2019 were previously reported in the 2019 notes to the consolidated financial statements as a component of other. The reclassification has no impact on the consolidated financial statements for the year ended December 31, 2019. 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 years ended December 31, 2020 and 2019, the amount of gross unrecognized tax benefits increased by $0.3 million and $39,000, respectively. 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, 2020 and 2019, such interest and penalties are not 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. The Company is currently under examination by the Israeli taxing authorities for 2019 and 2018. As of December 31, 2020, all tax years remain open to examination. In March 2020 and December 2020, the United States enacted the Coronavirus Aid, Relief, and Economic Security (“CARES”) Act and the Consolidated Appropriation Act (“CAA”), respectively, as a result of the COVID-19 pandemic, which contain among other things, numerous income tax provisions. Some of these tax provisions are expected to be effective retroactively for years ending before the date of enactment. The Company has evaluated the current legislation and at this time, does not anticipate the CARES Act or the CAA to have a material impact on its consolidated financial statements.

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Net Loss Per Share	10. Net Loss Per Share The following outstanding potentially dilutive shares, including all outstanding stock options, have been excluded from the calculation of diluted net loss per share for the periods presented due to their anti-dilutive effect: Year Ended December 31, 2020 2019 Stock options to purchase common stock 1,898,395 1,320,243 Shares available for future option grants 1,433,991 1,523,950 Total 3,332,386 2,844,193

Subsequent Event

Subsequent Event	12 Months Ended
	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Event

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
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.
Reclassification	Reclassification Certain prior year footnote amounts have been updated for consistency with the current year presentation. Such reclassification has no effect on the consolidated financial statements.
Foreign Currencies	Foreign Currencies Certain transactions during the years ended December 31, 2020 and 2019 were denominated in currencies other than the U.S. dollar. Gains and losses from foreign currency transactions were not material for all periods presented and are reflected in the consolidated statements of operations and comprehensive loss as a component of other expenses, net. The Company’s subsidiary in Lithuania uses the Euro as its functional currency for financial reporting. The re-measurement from Euros to U.S. dollars results in translation gain and loss adjustments, which are reflected as a component of comprehensive loss as foreign currency translation adjustments.
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 and certain accrued expenses. 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.
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. The ongoing COVID-19 pandemic has disrupted and may continue to disrupt the Company’s business and delay its preclinical and clinical programs and timelines. The Company does not yet know the full extent of potential delays to clinical trials, which could prevent or delay the Company from obtaining approval for BIO89-100.
Segment Reporting	Segment Reporting The Company has one operating
Cash and Cash Equivalents and Restricted Cash	Cash and Cash Equivalents 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 funds and commercial paper that are stated at fair value. Restricted Cash Restricted cash consists of a money market account that serves as collateral for the Company’s operating lease agreement for its facility in Israel.
Investments	Investments Investments have been classified as available-for-sale and are carried at estimated fair value as determined based upon quoted market prices or pricing models for similar securities. Management determines the appropriate classification of its investments in debt securities at the time of purchase. Generally, investments with original maturities beyond three months at the date of purchase are classified as short-term because it is management’s intent to use the investments to fund current operations or to make them available for current operations. Unrealized gains and losses are excluded from earnings and are reported as a component of comprehensive loss. The Company periodically evaluates whether declines in fair values of its available-for-sale securities below their book value are other-than-temporary. This evaluation consists of several qualitative and quantitative factors regarding the severity and duration of the unrealized loss as well as the Company’s ability and intent to hold the available-for-sale security until a forecasted recovery occurs. Additionally, the Company assesses whether it has plans to sell the security or it is more likely than not it will be required to sell any available-for-sale securities before recovery of its amortized cost basis. Realized gains and losses and declines in fair value judged to be other than temporary, if any, on available-for-sale securities are included in other expenses, net. The cost of investments sold is based on the specific-identification method. There are no material realized gains or losses on investments for the periods presented. Interest on available-for-sale securities is included in other expenses, net and is not material for all periods presented.
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 consolidated balance sheets and the resulting gains or losses are recorded in the consolidated statements of operations and comprehensive loss.
Impairment of Long-Lived Assets	Impairment The Company periodically
Accrued Research and Development Expenses	Accrued Research and Development Expenses The Company estimates preclinical The Company accrues for these
Leases	Leases The Company leases
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
Research and Development Expenses	Research and Research
Share-Based Compensation	Share-Based Compensation The Company measures The Company estimates The Black-Scholes • Expected volatility—Since the Company has limited trading history for its common stock due to its short trading history, the expected volatility is estimated based on the volatility of comparable publicly traded biotechnology companies during the equivalent period of the calculated expected term of the options granted. The comparable companies were chosen based on their similar size, stage in the life cycle or area of specialty. • Expected term—The expected term of options granted to employees and directors is determined using the “simplified” method. Under this approach, the expected term is presumed to be the midpoint between the weighted-average vesting term and the contractual term of the option. The simplified method makes the assumption that the employee will exercise share options evenly over the period when the share options are vested and ending on the date when the share options would expire. The expected option term for options granted to non-employees is estimated on a grant-by-grant basis. • Risk-free interest rate—The risk-free interest rate is based on the U.S. Treasury zero coupon bonds in effect on the grant date for periods with an equivalent expected term as the option. • Expected dividend—The Company has never paid dividends and has no foreseeable plans to pay dividends on its shares of common stock. Therefore, an expected dividend of zero is used.
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 loss is comprised of changes in unrealized gains or losses on available-for-sale securities and foreign currency translation adjustments.
Recently Adopted Accounting Standards	Recently Adopted Accounting Standards In August 2018, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) No. 2018-13, Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement
Recent Accounting Pronouncements	Recent Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02— Leases

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Summary of Financial Assets Measured at Fair Value on Recurring Basis	The following table presents the Company’s financial assets measured at fair value on a recurring basis by level within the fair value hierarchy as of December 31, 2020 (in thousands): As of December 31, 2020 Valuation Amortized Unrealized Unrealized Hierarchy Cost Gains Losses Fair Value Money market funds Level 1 $ 46,134 $ — $ — $ 46,134 Commercial paper Level 2 76,605 — (2 ) 76,603 Agency bonds Level 2 29,654 15 — 29,669 Corporate debt securities Level 2 11,890 — (6 ) 11,884 U.S. government bonds Level 2 7,093 — — 7,093 Municipal bonds Level 2 5,592 2 (1 ) 5,593 U.S. treasury bills Level 2 4,680 — — 4,680 Agency discount securities Level 2 200 — — 200 Total cash equivalents and available-for-sale securities $ 181,848 $ 17 $ (9 ) $ 181,856 Classified as: Cash equivalents $ 75,410 Short-term investments 106,446 Total cash equivalents and available-for-sale securities $ 181,856
Schedule of Contractual Maturities of Cash Equivalents and Available-for-Sale Securities	The following table summarizes the Company’s cash equivalents and available-for-sale securities by contractual maturity as of December 31, 2020 (in thousands): As of December 31, 2020 Within one year $ 160,304 After one year through two years 21,552 Total cash equivalents and available-for-sale securities $ 181,856
Summary of Changes in Fair Value of Level 3 Liability	For the year ended December 31, 2019, changes in the fair value of the Company’s Level 3 financial liability measured on a recurring basis were as follows (in thousands): Year Ended December 31, 2019 Beginning balance $ 1,671 Revaluation of convertible preferred stock liability recorded in other expenses (income), net 30,597 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 $ —
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: Year Ended December 31, 2019 Stock price $0.99-$2.57 Exercise price $1.00 Expected term (years) 0.00-2.25 Expected volatility 72.0 % Risk-free interest rate 0.0-2.4%

Consolidated Balance Sheet Co_2

Consolidated Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 2019 Computer equipment $ 105 $ 67 Furniture and office equipment 144 111 Total property and equipment 249 178 Less: accumulated depreciation (83 ) (23 ) Total property and equipment, net $ 166 $ 155
Schedule of Accrued Expenses	Accrued expenses consist of the following (in thousands): As of December 31, 2020 2019 Accrued research and development expenses $ 2,884 $ 2,326 Accrued employee and related expenses 2,552 1,396 Accrued professional and legal fees 453 573 Accrued other 159 325 Total accrued expenses $ 6,048 $ 4,620

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments Under Non-cancellable Operating Lease Obligations	Future minimum As of December 31, 2020 2021 $ 232 2022 8 Total future minimum annual payments $ 240

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2020
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): Year Ended December 31, 2020 2019 Research and development $ 1,250 $ 30 General and administrative 2,557 359 Total share-based compensation $ 3,807 $ 389
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: Year Ended December 31, 2020 2019 Expected term (years) 4.0-6.1 5.9-6.1 Contractual term (years) 10.0 10.0 Expected volatility 86.4-97.6% 61.8-87.6% Risk-free interest rate 0.2-1.5% 1.6-2.6% Expected dividend — —
Summary of Stock Option Activity	The following table summarizes stock option activity for the year ended December 31, 2020: 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, 2019 1,320,243 $ 3.34 9.23 $ 30,353 Granted 682,000 29.78 Exercised (63,366 ) 4.29 Cancelled (40,482 ) 2.87 Balance outstanding as of December 31, 2020 1,898,395 12.79 8.60 $ 25,918 Exercisable as of December 31, 2020 535,084 $ 2.58 8.11 $ 11,684

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Schedule of Effective Income Tax Rate of Company and Subsidiaries [Table Text Block]	As a result of the Reorganization described in Note 1, the Company is taxed according to U.S. federal and state tax laws and Israeli tax laws. The statutory tax rates applicable to the income of the Company and its subsidiaries are as follows: Year Ended December 31, 2020 2019 89bio, Inc. 21 % 21 % 89Bio Ltd 23 % 23 % 89bio Management, Inc. 21 % 21 % UAB 89bio Lithuania 15 % 15 %
Summary of Income Tax Benefit (Expense)	The income Year Ended December 31, 2020 2019 Current: Federal $ (11 ) $ (167 ) State 1 (1 ) Foreign — (30 ) Total (10 ) (198 ) Deferred: Federal 69 (20 ) Total 69 (20 ) Income tax benefit (expense) $ 59 $ (218 )
Summary of Components of Deferred Tax Assets	Significant As of December 31, 2020 2019 U.S. net operating loss carryforwards $ 11,342 $ 1,916 Israel net operating loss carryforwards 3,978 4,328 Research and development expenses 5,392 3,419 Accrued expenses 635 349 Other 658 10 Total deferred tax assets 22,005 10,022 Less: valuation allowance (21,936 ) (10,022 ) Net deferred tax assets $ 69 $ —
Summary of Loss from Continuing Operations Before Taxes on Income	The Company recorded a loss from continuing operations, before income tax for the periods indicated as follows (in thousands): Year Ended December 31, 2020 2019 United States $ (58,760 ) $ (19,502 ) Lithuania (73 ) 200 Israel 9,275 (37,900 ) Net loss before income tax $ (49,558 ) $ (57,202 )
Summary of Reconciliation of Income Tax Benefit (Expense) Statutory Tax Rate to Effective Tax Rate	The reconciliation Year Ended December 31, 2020 2019 Income tax benefit computed at statutory rates $ 8,285 $ 13,095 Research and development credits, net of uncertain tax position 815 93 Change in valuation allowance (11,914 ) (6,520 ) Change in Israel effective tax rate due to the 2019 reorganization 647 (734 ) Foreign rate differential 1,671 — Revaluation of convertible preferred stock liability — (6,039 ) Other 555 (113 ) Income tax benefit (expense) $ 59 $ (218 )

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Schedule of Outstanding Potentially Dilutive Securities Excluded From Calculation of Diluted Net Loss	The following outstanding potentially dilutive shares, including all outstanding stock options, have been excluded from the calculation of diluted net loss per share for the periods presented due to their anti-dilutive effect: Year Ended December 31, 2020 2019 Stock options to purchase common stock 1,898,395 1,320,243 Shares available for future option grants 1,433,991 1,523,950 Total 3,332,386 2,844,193

Organization and Basis of Pre_2

Organization and Basis of Presentation - Additional Information (Details) $ / shares in Units, $ in Thousands	1 Months Ended			12 Months Ended
	Sep. 30, 2020USD ($)$ / sharesshares	Jul. 31, 2020USD ($)$ / sharesshares	Nov. 30, 2019USD ($)$ / sharesshares	Dec. 31, 2020USD ($)shares	Dec. 31, 2019USD ($)shares	Nov. 13, 2019shares
Subsidiary Sale Of Stock [Line Items]
Date of incorporation				Jun. 30, 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
Proceeds from issuance of common stock, net of underwriters discount and commissions					$ 11
Cash and cash equivalents				$ 204,600
Common Stock
Subsidiary Sale Of Stock [Line Items]
Convertible preferred stock automatically converted into common stock | shares			7,077,366			7,077,366
Public Offerings | Common Stock
Subsidiary Sale Of Stock [Line Items]
Shares issued and sold | shares			6,100,390	6,072,040	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
Proceeds from issuance of common stock, net of underwriters discount and commissions			$ 87,700
Underwriters option | Common Stock
Subsidiary Sale Of Stock [Line Items]
Shares issued and sold | shares		397,440	795,703
Underwritten public offering | Common Stock
Subsidiary Sale Of Stock [Line Items]
Shares issued and sold | shares	3,025,000	3,047,040
IPO price per share | $ / shares	$ 28	$ 27.50
Proceeds from issuance of common stock	$ 79,500	$ 78,200
Payment of underwriting discounts, commissions	4,600	5,000
Other offering expenses	600	600
Gross proceeds from issue of common stock	84,700	83,800
Proceeds from issuance of common stock, net of underwriters discount and commissions	$ 79,500	$ 78,200

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)Segment
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments | Segment	1
Realized gains or losses on investments	$ 0
Capital contribution by the preferred stockholders	$ 25,600
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, 2020USD ($)
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	$ 181,848
Short-term investments, Gross Unrealized Holding Gains	17
Short-term investments, Gross Unrealized Holding Losses	(9)
Short-term investments, Aggregated Fair Value	181,856
Cash equivalents
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, Aggregated Fair Value	75,410
Short-term investments
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, Aggregated Fair Value	106,446
Level 1
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, Aggregated Fair Value	181,856
Within one year	160,304
After one year through two years	21,552
Level 1 | Money Market Funds
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	46,134
Short-term investments, Aggregated Fair Value	46,134
Level 2 | Commercial Paper
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	76,605
Short-term investments, Gross Unrealized Holding Losses	(2)
Short-term investments, Aggregated Fair Value	76,603
Level 2 | Agency bonds
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	29,654
Short-term investments, Gross Unrealized Holding Gains	15
Short-term investments, Aggregated Fair Value	29,669
Level 2 | U.S. government bonds
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	7,093
Short-term investments, Aggregated Fair Value	7,093
Level 2 | Corporate Debt
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	11,890
Short-term investments, Gross Unrealized Holding Losses	(6)
Short-term investments, Aggregated Fair Value	11,884
Level 2 | U.S. treasury bills
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	4,680
Short-term investments, Aggregated Fair Value	4,680
Level 2 | Agency discount securities
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	200
Short-term investments, Aggregated Fair Value	200
Level 2 | Municipal Bonds
Fair Value Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, Amortized Cost	5,592
Short-term investments, Gross Unrealized Holding Gains	2
Short-term investments, Gross Unrealized Holding Losses	(1)
Short-term investments, Aggregated Fair Value	$ 5,593

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details)	Dec. 31, 2020USD ($)
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value measurement, financial assets	$ 0
Level 3
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value measurement, financial liability	$ 0

Fair Value Measurements - Sum_2

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

Fair Value Measurements - Sum_3

Fair Value Measurements - Summary of Fair Value Assumptions (Details) - Convertible Preferred Stock Liability - Black Scholes Option Pricing Model	12 Months Ended
	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	0.99
Stock Price | Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	2.57
Exercise Price
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	1
Expected Term (Years) | Minimum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	0 years
Expected Term (Years) | Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	2 years 2 months 30 days
Expected Volatility
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	0
Risk-free Interest Rate | Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair Measurement Input	2.4

Consolidated Balance Sheet Co_3

Consolidated Balance Sheet Components - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Total property and equipment	$ 249	$ 178
Less: accumulated depreciation	(83)	(23)
Total property and equipment, net	166	155
Computer Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	105	67
Furniture and Office Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	$ 144	$ 111

Consolidated Balance Sheet Co_4

Consolidated Balance Sheet Components - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Depreciation expense for property and equipment	$ 60,000	$ 17,000

Consolidated Balance Sheet Co_5

Consolidated Balance Sheet Components - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued research and development expenses	$ 2,884	$ 2,326
Accrued employee and related expenses	2,552	1,396
Accrued professional and legal fees	453	573
Accrued other	159	325
Total accrued expenses	$ 6,048	$ 4,620

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($)	1 Months Ended			12 Months Ended
	Dec. 31, 2019	May 31, 2018	Apr. 30, 2018	Dec. 31, 2020	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 expires in April 2021 and the Company has an option to renew for an additional 12 months.
Operating lease, payments		$ 4,000		$ 17,500
Lessee, operating lease term of contract	24 months	12 months			24 months
Operating leases, rent expense				$ 273,000	$ 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				$ 0	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			$ 95,000	$ 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, 2020USD ($)
Commitments And Contingencies Disclosure [Abstract]
2021	$ 232
2022	8
Total future minimum annual payments	$ 240

Term Loan - Additional Informat

Term Loan - Additional Information (Details) - Loan Agreement	1 Months Ended
	Apr. 30, 2020USD ($)$ / sharesshares	Dec. 31, 2020USD ($)	Jul. 31, 2020
Debt Instrument [Line Items]
Credit facility maturity date	Sep. 1, 2023
Line of credit facility, description	In April 2020, the Company and certain of its subsidiaries entered into a Loan and Security Agreement (the “Loan Agreement”) with the lenders referred to therein (the “Lenders”), and Silicon Valley Bank, as collateral agent. The Loan Agreement provides for (i) a secured term A loan facility (the “Term A Loan Facility”) of up to $10.0 million and (ii) a secured term B loan facility (the “Term B Loan Facility”) of up to $5.0 million that is available upon the Company satisfying certain milestones. The Term A Loan Facility matures on November 1, 2022, provided, that if the Term B Loan Facility is funded, the facilities instead mature on September 1, 2023. The loans will bear interest at the greater of (i) 4.50% and (ii) the sum of (a) the Prime Rate as reported in The Wall Street Journal plus (b) 1.25%.
Warrant expiration date	Apr. 7, 2030		Jun. 30, 2025
Debt issuance costs, gross	$ 600,000	$ 600,000
Debt issuance costs		200,000
Dividends
Debt Instrument [Line Items]
Fair value of warrant assumptions, dividends	$ 0
Black Scholes Option Pricing Model | Risk-free Interest Rate
Debt Instrument [Line Items]
Fair Measurement Input	0.0075
Black Scholes Option Pricing Model | Expected Volatility
Debt Instrument [Line Items]
Fair Measurement Input	0.923
Black Scholes Option Pricing Model | Expected Term (Years)
Debt Instrument [Line Items]
Fair Measurement Input	10 years
Prime Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	1.25%
Minimum
Debt Instrument [Line Items]
Debt instrument, interest rate	4.50%
Term A Loan Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 10,000,000
Credit facility maturity date	Nov. 1, 2022
Amount drawn		0
Warrants to purchase common stock | shares	25,000
Warrant exercise price | $ / shares	$ 22.06
Term B Loan Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 5,000,000
Amount drawn		$ 0
Warrants to purchase common stock | shares	8,333

Convertible Preferred Stock - A

Convertible Preferred Stock - Additional Information (Details) - USD ($)	Nov. 13, 2019	Dec. 31, 2019	Dec. 31, 2020	Nov. 30, 2019	Apr. 30, 2018
Temporary Equity [Line Items]
Per share price of issuance of shares		$ 0.001	$ 0.001
Capital contribution related to extinguishment of convertible preferred stock liability	$ 25,600,000	$ 25,595,000
Common Stock
Temporary Equity [Line Items]
Convertible preferred stock automatically converted into common stock	7,077,366			7,077,366
Series A Convertible Preferred Stock
Temporary Equity [Line Items]
Number of shares committed to purchase, no longer issuable	16,000,000
Series A Share Purchase Agreement | Series A Convertible Preferred Stock
Temporary Equity [Line Items]
Per share price of issuance of shares					$ 1
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

Share-Based Compensation - Addi

Share-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended
	Oct. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares issued		19,931,660	13,788,982
ESPP Purchases
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%
First offering period	6 months
Commencement date of first six month offering period	Jan. 1, 2020
Second offering period	6 months
Commencement date of second six month offering period	Jul. 1, 2020
Common stock, shares issued		7,272
Number of shares of common stock available for issuance under ESPP		355,806
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%
Common stock reserved and available for issuance as future option grants		1,433,991
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
Unrecognized stock option granted under plan		$ 13.5
Unrecognized weighted average period		2 years 6 months
2020 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Estimated total grant date fair value of options vested		$ 800,000
Weighted average fair value options granted		$ 21.88	$ 2.90
Maximum | ESPP Purchases
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	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation	$ 3,807	$ 389
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation	1,250	30
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation	$ 2,557	$ 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)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Contractual term (years)	P10Y	P10Y
Expected volatility, minimum	86.40%	61.80%
Expected volatility, maximum	97.60%	87.60%
Risk-free interest rate, minimum	0.20%	1.60%
Risk-free interest rate, maximum	1.50%	2.60%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	4 years	5 years 10 months 24 days
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 years 1 month 6 days	6 years 1 month 6 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, 2019	Dec. 31, 2020
Number of Options
Outstanding, Beginning Balance		1,320,243
Granted		682,000
Exercised		(63,366)
Cancelled		(40,482)
Outstanding, Ending Balance	1,320,243	1,898,395
Exercisable as of December 31, 2020		535,084
Weighted Average Exercise Price
Weighted Average Exercise Price Outstanding, Beginning Balance		$ 3.34
Weighted Average Exercise Price, Granted		29.78
Weighted Average Exercise Price, Exercised		4.29
Weighted Average Exercise Price, Cancelled		2.87
Weighted Average Exercise Price Outstanding, Ending Balance	$ 3.34	12.79
Weighted Average Exercise Price, Exercisable as of December 31, 2019		$ 2.58
Weighted Average Remaining Contractual Term (In years)
Weighted Average Remaining Contractual Term (In years), Outstanding	9 years 2 months 23 days	8 years 7 months 6 days
Weighted Average Remaining Contractual Term (In years), Exercisable as of December 31, 2019		8 years 1 month 9 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value Outstanding		$ 30,353
Aggregate Intrinsic Value Outstanding	$ 30,353	25,918
Aggregate Intrinsic Value, Exercisable as of December 31, 2019		$ 11,684

Income Taxes - Summary of Statu

Income Taxes - Summary of Statutory Tax Rates Applicable to Income of Company and Subsidiaries (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Line Items]
Effective income tax rate	21.00%	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 - Income Taxes - S

Income Taxes - Income Taxes - Summary of Income Tax Benefit (Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Current:
Federal	$ (11)	$ (167)
State	1	(1)
Foreign		(30)
Total	(10)	(198)
Deferred:
Federal	69	(20)
Total	69	(20)
Income tax benefit (expense)	$ (59)	$ 218

Income Taxes - Summary of Compo

Income Taxes - Summary of Components of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Line Items]
Research and development expenses	$ 5,392	$ 3,419
Accrued expenses	635	349
Other	658	10
Total deferred tax assets	22,005	10,022
Less: valuation allowance	(21,936)	(10,022)
Net deferred tax assets	69
United States
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	11,342	1,916
Israel
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 3,978	$ 4,328

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Line Items]
Deferred tax assets, valuation allowance	$ 21,936,000	$ 10,022,000
Deferred tax assets, change in valuation allowance	$ 11,900,000	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%
Federal research and development credit carryforwards	$ 600,000
State research and development credit carryforwards	700,000	200,000
Increase in unrecognized tax benefits	300,000	39,000
Unrecognized Tax Benefits	0
United States
Income Tax Disclosure [Line Items]
Deferred tax assets, change in valuation allowance		20,000,000
Accumulated tax loss carryforward	54,100,000	9,100,000
Israel
Income Tax Disclosure [Line Items]
Deferred tax assets, change in valuation allowance	(69,000)
Accumulated tax loss carryforward	$ 17,300,000	$ 23,800,000

Income Taxes - Summary of Loss

Income Taxes - Summary of Loss from Continuing Operations Before Taxes on Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Line Items]
Net loss before income tax	$ (49,558)	$ (57,202)
United States
Income Tax Disclosure [Line Items]
Net loss before income tax	(58,760)	(19,502)
Lithuania
Income Tax Disclosure [Line Items]
Net loss before income tax	(73)	200
Israel
Income Tax Disclosure [Line Items]
Net loss before income tax	$ 9,275	$ (37,900)

Income Taxes - Summary of Recon

Income Taxes - Summary of Reconciliation of Income Tax Benefit (Expense) Statutory Tax Rate to Effective Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income tax benefit computed at statutory rates	$ 8,285	$ 13,095
Research and development credits, net of uncertain tax position	815	93
Change in valuation allowance	(11,914)	(6,520)
Change in Israel effective tax rate due to the 2019 reorganization	647	(734)
Foreign rate differential	1,671
Revaluation of convertible preferred stock liability		(6,039)
Other	555	(113)
Income tax benefit (expense)	$ 59	$ (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	12 Months Ended
	Dec. 31, 2020	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	3,332,386	2,844,193
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	1,898,395	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	1,433,991	1,523,950