0000950170-21-001740 | 10-Q | XBRL Viewer

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Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2021	Sep. 09, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Entity Central Index Key	0001739410
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Document Period End Date	Jun. 30, 2021
Current Fiscal Year End Date	--12-31
Entity File Number	001-40693
Entity Registrant Name	RALLYBIO CORPORATION
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	85-1083789
Entity Address, Address Line One	234 Church Street
Entity Address, Address Line Two	Suite 1020
Entity Address, City or Town	New Haven
Entity Address, State or Province	CT
Entity Address, Postal Zip Code	06510
City Area Code	203
Local Phone Number	859-3820
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Trading Symbol	RLYB
Security Exchange Name	NASDAQ
Document Quarterly Report	true
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Document Transition Report	false
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Bankruptcy Proceedings, Reporting Current	true
Entity Common Stock, Shares Outstanding		32,129,970

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 112,729	$ 140,233
Prepaid expenses and other assets	5,702	1,028
Total current assets	118,431	141,261
Property and equipment, net	306	287
Investment in joint venture	1,360	310
Total assets	120,097	141,858
Current liabilities:
Accounts payable	2,622	1,579
Accrued expenses	4,786	4,264
Total current liabilities	7,408	5,843
Accrued expenses long-term	27	12
Total liabilities	7,435	5,855
Commitments and contingencies (Note 7)
Members' deficit:
Common units, value	536	452
Incentive units, value	1,515	538
Accumulated deficit	(71,416)	(47,014)
Total members' deficit	(69,365)	(46,024)
Total liabilities, redeemable convertible preferred units, and members' deficit	120,097	141,858
Series A Preferred Units
Temporary Equity [Abstract]
Redeemable convertible preferred units, value	37,141	37,141
Series B Preferred Units
Temporary Equity [Abstract]
Redeemable convertible preferred units, value	$ 144,886	$ 144,886

Condensed Consolidated Balance Sheet (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Common Stock, Par or Stated Value Per Share	$ 0	$ 0
Common Stock, Shares, Issued	5,700,000	5,700,000
Common Stock, Shares, Outstanding	5,700,000	5,700,000
Incentive Units Shares Issued	20,869,704	6,865,704
Incentive Units Shares Outstanding	20,869,704	6,865,704
Series A Preferred Stock [Member]
Temporary Equity, Par or Stated Value Per Share	$ 0	$ 0
Temporary Equity, Shares Authorized	33,478,255	33,478,255
Temporary Equity, Shares Issued	33,478,255	33,478,255
Temporary Equity, Shares Outstanding	33,478,255	33,478,255
Temporary Equity, Liquidation Preference	$ 37,600	$ 37,600
Series B Preferred Stock [Member]
Temporary Equity, Par or Stated Value Per Share	$ 0	$ 0
Temporary Equity, Shares Authorized	104,442,965	104,442,965
Temporary Equity, Shares Issued	104,442,965	104,442,965
Temporary Equity, Shares Outstanding	104,442,965	104,442,965
Temporary Equity, Liquidation Preference	$ 145,204	$ 145,204

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Operating Expenses:
Research and development	$ 6,818	$ 3,092	$ 15,855	$ 5,005
General and administrative	3,712	1,570	7,499	3,501
Total operating expenses	10,530	4,662	23,354	8,506
Loss from operations	(10,530)	(4,662)	(23,354)	(8,506)
Other income (expenses):
Interest income	13	47	30	102
Interest expense	0	12	10	24
Other (expense) income	(142)	69	(118)	121
Total other (expense) income, net	(129)	104	(98)	199
Loss before income taxes	(10,659)	(4,558)	(23,452)	(8,307)
Income tax benefit	0	0	0	(16)
Loss on investment in joint venture	468	335	950	483
Net loss and comprehensive loss	(11,127)	(4,893)	(24,402)	(8,774)
Net loss attributable to common units	$ (11,127)	$ (4,893)	$ (24,402)	$ (8,774)
Net loss per common unit, basic and diluted	$ (2.80)	$ (1.85)	$ (6.77)	$ (3.81)
Weighted average common units outstanding, basic and diluted	3,978,054	2,643,750	3,603,193	2,304,385

Condensed Consolidated Statements of Changes in Redeemable Convertible Preferred Units and Members Deficit (Unaudited) - USD ($) $ in Thousands	Total	Series A Redeemable Convertible Preferred Units	Series B Redeemable Convertible Preferred Units [Member]	Common Units	Incentive Units	Accumulated Deficit
Beginning Balance at Dec. 31, 2019	$ (20,281)			$ 230	$ 56	$ (20,567)
Beginning Balance (in shares) at Dec. 31, 2019				5,700,000	1,633,000
Balance at Dec. 31, 2019		$ 37,141	$ 0
Balance (in shares) at Dec. 31, 2019		33,478,255	0
Issuance of Series B Redeemable Convertible Preferred Units, net of issuance costs			$ 144,886
Issuance of Series B Redeemable Convertible Preferred Units, net of issuance costs (shares)			104,442,965
Incentive unit-based compensation	74				$ 74
Incentive unit-based compensation (shares)					225,000
Common unit-based compensation	125			$ 125
Net loss and comprehensive loss	(8,774)					(8,774)
Balance (in shares) at Jun. 30, 2020		33,478,255	104,442,965
Balance at Jun. 30, 2020		$ 37,141	$ 144,886
Ending Balance (in shares) at Jun. 30, 2020				5,700,000	1,858,000
Ending Balance at Jun. 30, 2020	(28,856)			$ 355	$ 130	(29,341)
Beginning Balance at Mar. 31, 2020	(24,057)			$ 300	$ 91	(24,448)
Beginning Balance (in shares) at Mar. 31, 2020				5,700,000	1,633,000
Balance at Mar. 31, 2020		$ 37,141	$ 90,857
Balance (in shares) at Mar. 31, 2020		33,478,255	61,457,763
Issuance of Series B Redeemable Convertible Preferred Units, net of issuance costs			$ 54,029
Issuance of Series B Redeemable Convertible Preferred Units, net of issuance costs (shares)			42,985,202
Incentive unit-based compensation	39				$ 39
Incentive unit-based compensation (shares)					225,000
Common unit-based compensation	55			$ 55
Net loss and comprehensive loss	(4,893)					(4,893)
Balance (in shares) at Jun. 30, 2020		33,478,255	104,442,965
Balance at Jun. 30, 2020		$ 37,141	$ 144,886
Ending Balance (in shares) at Jun. 30, 2020				5,700,000	1,858,000
Ending Balance at Jun. 30, 2020	(28,856)			$ 355	$ 130	(29,341)
Beginning Balance at Dec. 31, 2020	(46,024)			$ 452	$ 538	(47,014)
Beginning Balance (in shares) at Dec. 31, 2020				5,700,000	6,865,704
Balance at Dec. 31, 2020		$ 37,141	$ 144,886
Balance (in shares) at Dec. 31, 2020		33,478,255	104,442,965
Incentive unit-based compensation	977				$ 977
Incentive unit-based compensation (shares)					14,004,000
Common unit-based compensation	84			$ 84
Net loss and comprehensive loss	(24,402)					(24,402)
Balance (in shares) at Jun. 30, 2021		33,478,255	104,442,965
Balance at Jun. 30, 2021		$ 37,141	$ 144,886
Ending Balance (in shares) at Jun. 30, 2021				5,700,000	20,869,704
Ending Balance at Jun. 30, 2021	(69,365)			$ 536	$ 1,515	(71,416)
Beginning Balance at Mar. 31, 2021	(58,777)			$ 494	$ 1,018	(60,289)
Beginning Balance (in shares) at Mar. 31, 2021				5,700,000	19,934,704
Balance at Mar. 31, 2021		$ 37,141	$ 144,886
Balance (in shares) at Mar. 31, 2021		33,478,255	104,442,965
Incentive unit-based compensation	497				$ 497
Incentive unit-based compensation (shares)					935,000
Common unit-based compensation	42			$ 42
Net loss and comprehensive loss	(11,127)					(11,127)
Balance (in shares) at Jun. 30, 2021		33,478,255	104,442,965
Balance at Jun. 30, 2021		$ 37,141	$ 144,886
Ending Balance (in shares) at Jun. 30, 2021				5,700,000	20,869,704
Ending Balance at Jun. 30, 2021	$ (69,365)			$ 536	$ 1,515	$ (71,416)

Condensed Consolidated Statements of Changes in Redeemable Convertible Preferred Units and Members Deficit (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020
Series B Redeemable Convertible Preferred Units [Member]
Issuance costs	$ 71	$ 319

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash Flows from Operating Activities:
Net loss	$ (24,402)	$ (8,774)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	48	27
Equity based compensation	1,061	199
Loss on investment in joint venture	950	483
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(2,249)	(679)
Accounts payable	787	(449)
Accrued expenses	(970)	38
Net cash used in operating activities	(24,775)	(9,155)
Cash Flows used in Investing Activities:
Purchase of property and equipment	(66)	(8)
Investment in joint venture	(2,000)	(1,585)
Net cash used in investing activities	(2,066)	(1,593)
Cash Flows from Financing Activities:
Issuance of Series B preferred units	0	145,205
Preferred unit issuance costs	0	(307)
Payments of deferred offering costs	(663)	0
Net cash (used in) provided by financing activities	(663)	144,898
Net (decrease) increase in cash and cash equivalents	(27,504)	134,150
Cash and cash equivalents - beginning of period	140,233	19,458
Cash and cash equivalents - end of period	112,729	153,608
Supplemental Disclosures of Noncash Investing and Financing Activities:
Deferred offering costs in accounts payable and accrued expenses	1,762	0
Property and equipment in accounts payable and accrued expenses	15	6
Series B preferred unit issuance costs in accounts payable and accrued expenses	$ 0	$ 12

Business and Liquidity

6 Months Ended

Jun. 30, 2021

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Business and Liquidity

1. BUSINESS AND LIQUIDITY

As of June 30, 2021, Rallybio Holdings LLC (“Rallybio Holdings”) held 100% of the outstanding common stock of Rallybio Corporation. Rallybio Holdings had no activities other than its ownership in Rallybio Corporation. Rallybio Corporation held 100% of the outstanding membership units in four wholly-owned subsidiaries—Rallybio, LLC, Rallybio IPA, LLC, Rallybio IPB, LLC, and IPC Research, LLC (collectively, the “Company”). The Company is a clinical-stage biotechnology company built around a team of seasoned industry experts with a shared purpose and a track record of success in discovering, developing, manufacturing, and delivering therapies to meaningfully improve the lives of patients suffering from severe and rare diseases.

In August 2021, the Company completed its initial public offering (“IPO”), pursuant to which it issued and sold 7,130,000 shares of the Company’s common stock, inclusive of 930,000 shares sold pursuant to the full exercise of the underwriters’ option to purchase additional shares, at a public offering price of $13.00 per share. The gross proceeds from the IPO, including the exercise of the underwriter's option to purchase additional shares were $92.7 million and the net proceeds were approximately $83.2 million, after deducting underwriting discounts and commissions and other offering expenses.

Prior to the IPO, the Company operated as Rallybio Holdings, a Delaware limited liability company which was incorporated in Delaware on March 22, 2018 and held 100% of the outstanding membership units in five wholly-owned subsidiaries; Rallybio, LLC, Rallybio IPA, LLC, Rallybio IPB, LLC, Rallybio, IPD, LLC, and IPC Research, LLC prior to the IPO and it's liquidation. On June 30, 2021, the Company completed a series of transactions pursuant to which (i) Rallybio IPD, LLC, a direct subsidiary of Rallybio Holdings that was formed in Delaware in May 2020, was converted from a Delaware limited liability company to a Delaware corporation and changed its name to Rallybio Corporation (the "Corporation"), and (ii) four direct subsidiaries of the Corporation, each a Delaware limited liability company, or collectively the Merger Subs, each consummated a separate merger with one of Rallybio Holdings direct subsidiaries, other than Rallybio IPD, LLC, or collectively the Asset Subsidiaries, with the Asset Subsidiaries surviving the mergers and Rallybio Holdings receiving common stock of the Corporation in exchange for its interest in each Asset Subsidiary, which resulted in the Asset Subsidiaries becoming subsidiaries of the Corporation and the Corporation becoming the only direct subsidiary of Rallybio Holdings. On July 28, 2021, immediately prior to the completion of the IPO, Rallybio Holdings liquidated and distributed 100% of the capital stock of the Corporation, consisting solely of common stock, to the unitholders of Rallybio Holdings. The liquidation of Rallybio Holdings and distribution of the capital stock of the Corporation to the unitholders of Rallybio Holdings is referred to as the “Liquidation” and to the Liquidation and these other transactions collectively referred to as the “Reorganization.” As a result of the Reorganization, the unitholders of Rallybio Holdings became the holders of common stock of the Corporation, and the Company's condensed consolidated financial statements are subsequently reported from the Corporation.

Except as disclosed in this Quarterly Report on Form 10-Q, the unaudited condensed consolidated financial statements for the three and six months ended June 30, 2021 and 2020 and the notes thereto, and other financial information included in this Quarterly Report on Form 10-Q are those of Rallybio Holdings and do not give effect to the Reorganization.

Rallybio Holdings had cash and cash equivalents of $112.7 million at June 30, 2021. Rallybio Holdings currently expects that its cash and cash equivalents will be sufficient to fund its operating expenses and capital requirements for more than 12 months from the date the condensed consolidated financial statements are issued. However, we do not anticipate that the current cash and cash equivalents as of June 30, 2021 combined with our net proceeds from our IPO in August of 2021, will be sufficient for us to fund any of our product candidates through regulatory approval, and we will need to raise substantial additional capital to complete the development and commercialization of our product candidates, if approved. We may satisfy our future cash needs through the sale of equity securities, debt financings, working capital lines of credit, corporate collaborations or license agreements, grant funding, interest income earned on invested cash balances or a combination of one or more of these sources.

In March 2020, the World Health Organization characterized the novel coronavirus as a global pandemic. Although there is significant uncertainty as to the likely effects this disease may have in the future, to date there has not yet been a significant impact to the Company’s operations or financial statements.

Summary of Significant Accounting Policies Basis of Presentation and Principles of Consolidation

6 Months Ended

Jun. 30, 2021

Accounting Policies [Abstract]

Summary of Significant Accounting Policies Basis of Presentation and Principles of Consolidation

2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES BASIS OF PRESENTATION AND PRINCIPLES OF CONSOLIDATION

Unaudited Financial Information— The unaudited condensed consolidated financial statements of Rallybio Holdings have been prepared in conformity with accounting principles generally accepted in the United States of America ("GAAP"), and pursuant to the rules and regulations of the Securities and Exchange Commission (the "SEC"). In the opinion of Rallybio Holdings, the information furnished reflects all adjustments, all of which are of a normal and recurring nature, necessary for a fair presentation of the financial position and results of operations for the reported interim periods. Rallybio Holdings considers events or transactions that occur after the balance sheet date but before the financial statements are issued to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. The results of operations for interim periods are not necessarily indicative of results to be expected for the full year or any other interim period.

Rallybio Holdings reviews new accounting standards as issued. As of June 30, 2021 Rallybio Holdings has not identified any new standards that it believes will have a significant impact on the financial statements of Rallybio Holdings. However, Rallybio Holdings is still evaluating the impact of adopting ASU 2016-02, Leases on its condensed consolidated financial statements.

There were no changes to significant accounting policies of Rallybio Holdings during the six months ended June 30, 2021 other than noted below.

These accompanying unaudited condensed consolidated financial statements and notes should be read in conjunction with the audited consolidated financial statements for the year ended December 31, 2020 and notes thereto contained in the Company’s final prospectus for its IPO filed with the SEC on July 30, 2021 pursuant to Rule 424(b)(4) under the Securities Act of 1933, as amended (the “IPO Prospectus”).

Deferred Offering Costs—Rallybio Holdings capitalizes incremental legal, professional accounting and other third-party fees that are directly associated with the IPO as other current assets until the IPO is consummated. After consummation of the IPO, these costs will be recorded as a reduction of additional paid-in-capital generated as a result of the offering. As of June 30, 2021, there were deferred offering costs of approximately $2.4 million included in prepaid expenses and other assets. The IPO was completed in August of 2021 and all deferred offering costs were subsequently recorded within stockholder's equity of the Corporation as a reduction of additional paid-in-capital generated from the offering.

Accrued Expenses

6 Months Ended

Jun. 30, 2021

Accrued Liabilities, Current [Abstract]

Accrued Expenses

3. ACCRUED EXPENSES

Accrued expenses consisted of the following as of June 30, 2021 and December 31, 2020:


(in thousands)	JUNE 30, 2021		DECEMBER 31, 2020
Professional fees	$	1,628	$	185
Research and development		1,423		1,065
Employee expenses		1,321		1,912
Other		414		112
Asset purchase obligation		—		990
	$	4,786	$	4,264

Redeemable Convertible Preferred Units

6 Months Ended

Jun. 30, 2021

Features of Convertible Preferred Stock [Abstract]

Redeemable Convertible Preferred Units

4. REDEEMABLE CONVERTIBLE PREFERRED UNITS

Preferred Units—In April 2018, Rallybio Holdings entered into a Series A Preferred Stock Purchase Agreement (the “Series A Agreement”) with a total potential aggregate purchase price of $37.0 million. Under the terms of the Series A Agreement, Rallybio Holdings agreed to sell 5,999,999 units of Series A-1 Redeemable Convertible Preferred Units (“Series A-1 Units”) to investors at a price of $1.00 per share and up to 26,956,516 shares of Series A-2 Redeemable Convertible Preferred Units (“Series A-2 Units”), upon the achievement by Rallybio Holdings and its subsidiaries of certain milestone events, to investors at a price of $1.15 per share (the “Series A Financing Right Obligation”).

In April 2018, Rallybio Holdings sold 5,549,999 Series A-1 Units to investors in exchange for $5.5 million. Additionally, Rallybio Holdings issued 450,000 Series A-1 Units to Rallybio Holdings founders in exchange for a capital contribution of convertible debt totaling $0.5 million owed to the founders by Rallybio, LLC.

In connection with the Series A Agreement, Rallybio Holdings entered into a Connecticut Presence Agreement (the “CPA”) with Connecticut Innovation, Incorporated (“CII”) relating to Series A-1 and Series A-2 Units that would be issued to CII. The CPA provides that the proceeds from CII’s investment in Rallybio Holdings preferred units be paid back to CII at a specified price. The CPA was only exercisable upon Rallybio Holdings breach of the covenant which required it to maintain a Connecticut presence, as defined within the CPA.

In connection with the Series A Agreement, Rallybio Holdings granted investors the right to purchase Series A-2 Units at future milestone dates and at a predetermined price. Since the investors held rights that imposed an obligation on Rallybio Holdings to issue Preferred Units that were potentially redeemable, the future tranche rights were considered a freestanding instrument and were recorded at the fair value of the tranche right and classified as a liability. Changes in the fair value of this liability are recorded in prior period earnings. The milestones were met during 2019.

In 2019, upon the achievement of the certain milestones, Rallybio Holdings sold 27,478,256 Series A-2 Units to investors, founders and employees in exchange for $31.6 million.

In March 2020 Rallybio Holdings entered into a Series B Preferred Stock Purchase Agreement (the “Series B Agreement”) with a total aggregate purchase price of $91.1 million. Under the terms of the Series B Agreement, Rallybio Holdings agreed to sell 61,457,763 units of Series B Redeemable Convertible Preferred Units (“Series B Units”) to investors at a price of $1.48 per share. Rallybio Holdings received proceeds of $85.1 million as of March 31, 2020. The remaining $6.0 million was received on April 1, 2020.

In April and May 2020, Rallybio Holdings entered into subsequent offerings of the Series B Agreement increasing the total aggregate purchase price to $145.2 million. Under the terms of the updated Series B Agreement, Rallybio Holdings agreed to sell 104,442,965 total Series B Units to investors at a price of $1.39028 per share. An additional 4.2 million units were granted to investors in May 2020 who participated in prior offerings.

In August of 2021, the Company completed the IPO and Rallybio Holdings was liquidated as part of the Reorganization. The holders of Series A-1 preferred units and Series A-2 preferred units received an aggregate of 5,257,590 shares of Rallybio Corporation common stock, and the holders of Series B preferred units received an aggregate of 16,402,235 shares of Rallybio Corporation common stock.

Prior to the Reorganization, the Series A and B Preferred Units, (“preferred units”) had the following rights, preferences, and privileges:

Voting Rights—The holders of the preferred units were entitled to vote together as a single class and on an as converted to common units basis in accordance with each such holder’s percentage interests. In addition, the preferred units holders had the right to vote separately as a series on any matter which would adversely alter or change the rights, powers or preferences of one series without a similar effect on the other series.

Conversion Rights—Each preferred unit was convertible, at the option of the holder thereof, at any time and from time to time, and without the payment of additional consideration, into fully paid and nonassessable common units. The number of common units into which each preferred unit could have been converted was to be determined by dividing the number of preferred units by their applicable original issue price, potentially subject to adjustment for anti-dilution provisions.

Each preferred unit was automatically converted into fully paid and nonassessable common units upon either the closing of the sale of common units to the public at a price of at least $2.08542 per unit in a firm commitment underwritten public offering pursuant to an effective registration statement under the Securities Act of 1933, as amended, resulting in at least $50.0 million of gross proceeds to Rallybio Holdings, or at the occurrence of an event, specified in writing by the preferred units holders.

Dividends—The holders of preferred units were entitled to receive distributions declared and paid on the preferred units when determined by Rallybio Holdings Board of Managers. Rallybio Holdings was not permitted to declare, pay or set aside any distributions on any common units unless the preferred units holders first received, or simultaneously received, a distribution on each outstanding preferred unit in an amount at least equal to the greater of 8% of the applicable original issue price of the preferred units, per year, from and after the date of the issuance on a non-cumulative basis of any preferred units or the pro-rata distribution that the preferred units holder would receive had they converted their preferred units into common units.

No dividends were declared or paid during the three and six months ended June 30, 2021 and 2020.

Redemption Rights—The preferred units were only redeemable pursuant to a deemed liquidation event.

Anti-Dilution Provisions—If Rallybio Holdings made adjustments to any class of units for dividends, splits, combinations or other similar events, or issues additional securities at a purchase price less than the then current conversion price for issued and outstanding preferred units, the preferred units conversion price was to be adjusted in accordance with a formula, as defined in Rallybio Holdings Operating Agreement.

Liquidation—The preferred units had preferential rights with respect to any dissolution or liquidation of Rallybio Holdings and with respect to a sale of Rallybio Holdings. In the event of a dissolution, liquidation, or winding-up of Rallybio Holdings, the holders of the preferred units were entitled to receive, in preference to the holders of the common units and the incentive units, an amount equal to their original issue price. After payment of this preferential amount, remaining proceeds were to be distributed in accordance with a formula as defined in the Operating Agreement for Rallybio Holdings. This formula provided additional preferences to the preferred unit holders.

Members' Deficit

6 Months Ended

Jun. 30, 2021

Members' Equity [Abstract]

MEMBERS' DEFICIT

5. MEMBERS’ DEFICIT

Common Units—As of June 30, 2021 and December 31, 2020, Rallybio Holdings had authorized 165,393,580 and 161,393,580 common units, respectively, pursuant to the terms of Rallybio Holdings Operating Agreement, which included 137,921,220 common units reserved for issuance upon conversion of preferred units. Additionally, of the total common units authorized, 22,972,360 and 18,972,360 common units were reserved for issuance to officers and employees of Rallybio Holdings pursuant to the Rallybio Holdings, LLC 2018 Share Plan (“2018 Share Plan”) at June 30, 2021 and December 31, 2020, respectively.

In 2018, Rallybio Holdings issued 4,500,000 common units to its founders, including 3,375,000 common units that were to vest over a four year period. In 2018, Rallybio Holdings also issued 1,200,000 restricted common units to the founders, pursuant to restricted share purchase agreements, which were to begin vesting upon achievement of certain performance conditions. These restricted common units were to vest into common units and therefore have been presented as common units within the condensed consolidated statement of changes in redeemable convertible preferred units and members’ deficit. Restricted common units issued to the founders were to vest 25% upon the 1-year anniversary of Rallybio Holdings initiating a clinical program through one of its controlled subsidiaries, and monthly thereafter over the next 36 months. In 2019, it was determined that the performance condition of these restricted common units became probable, vesting started, and the units started expensing over the vesting period. No other common or restricted common units were granted or forfeited in the six months ended June 30, 2021. Each common unit entitled the holder to one vote on all matters submitted to a vote of Rallybio Holdings members. The weighted average fair value of both the 4,500,000 common units and 1,200,000 restricted common units granted during 2018 was $0.15.

As of June 30, 2021 and December 31, 2020, of the 4,500,000 common units issued to the founders, 3,656,250 and 2,812,500 of these restricted common units were fully vested, respectively, and 843,750 and 1,687,500 units remained unvested, respectively. During both the three months ended June 30, 2021 and 2020, Rallybio Holdings recognized equity-based compensation expense relating to the issuance of these restricted common units of $31,641 and for both the six months ended June 30, 2021 and 2020, Rallybio Holdings recognized equity-based compensation expense of $63,281.

At June 30, 2021 and December 31, 2020, of the 1,200,000 restricted common units issued to the founders that were issued subject to performance-based vesting conditions, 525,000 and 375,000 of these restricted common units were fully vested, respectively and 675,000 and 825,000 units remained unvested, respectively. During the three months ended June 30, 2021 and 2020, Rallybio Holdings recognized equity-based compensation expense of $10,461 and $23,630, respectively and $20,923 and $62,132 during the six months ended June 30, 2021 and 2020, respectively on these restricted common units.

Incentive Units—As of June 30, 2021 and December 31, 2020, Rallybio Holdings was authorized to issue up to an aggregate of 22,972,360 and 18,972,360 incentive units, respectively pursuant to the Plan. The reserve included 1,200,000 restricted common units that were issued to founders in 2018. Incentive units were granted to employees and generally vest over a four year period. As of June 30, 2021, 902,656 incentive units, remained available for future grants.

During the three months ended June 30, 2021 and 2020, Rallybio Holdings granted 935,000 and 225,000 incentive units to employees under the Plan, respectively and 14,004,000 and 225,000 incentive units during the six months ended June 30, 2021 and 2020, respectively. The weighted average fair value of incentive units granted to employees in the three months ended June 30, 2021 and 2020 was $1.53 and $0.40 per unit, respectively and $0.41 and $0.40 for the six months ended June 30, 2021 and 2020, respectively.

During the three months ended June 30, 2021 and 2020, Rallybio Holdings recognized equity-based compensation expense of $497,015 and $38,620, respectively and $976,791 and $73,208 during the six months ended June 30, 2021 and 2020, respectively, relating to the issuance of incentive units.

The assumptions that went into the option pricing models for determining the fair value of Rallybio Holdings incentive units granted for the six months ended June 30, 2021 and 2020 are as follows:


	SIX MONTHS ENDED JUNE 30,
	2021		2020
Expected volatility	71.7% - 99.5%			95.0	%
Expected term (years)	0.58 - 1.00			1.50
Risk free interest rate	0.04% - 0.10%			0.16	%
Expected dividend yield		—		—
Fair value of underlying common units	$0.47 - $1.91		$	0.44

The following table provides a summary of the activity for the six months ended June 30, 2021 under the 2018 Share Plan for incentive units granted to employees:


	INCENTIVE UNITS		WEIGHTED AVERAGE GRANT DATE FAIR VALUE
Outstanding at December 31, 2020		6,865,704	$	0.41
Granted		14,004,000	$	0.41
Forfeited		—
Outstanding at June 30, 2021		20,869,704	$	0.41

At June 30, 2021 and December 31, 2020, Rallybio Holdings had 20,869,704 and 6,865,704 incentive units granted under the 2018 Share Plan that are outstanding and expected to vest, respectively. At June 30, 2021 and December 31, 2020, 2,181,052 and 495,182 incentive units were fully vested, respectively.

Equity-based compensation, including common and incentive units are classified in the condensed consolidated statements of operations and comprehensive loss for the three and six months ended June 30, 2021 and 2020 as follows:


	THREE MONTHS ENDED JUNE 30,				SIX MONTHS ENDED JUNE 30,
(in thousands)	2021		2020		2021		2020
Research and Development	$	193	$	37	$	354	$	60
General and Administrative		346		57		707		139
	$	539	$	94	$	1,061	$	199

In connection with the IPO of Rallybio Corporation the following items were approved by the board of directors:



the 2021 Equity Incentive Plan was approved which includes 5,440,344 shares of common stock reserved for future issuances of shares to employees, directors and consultants;



the 2021 Employee Stock Purchase Plan, or ESPP, was approved which includes 291,324 shares of common stock reserved for future issuances under this plan;



the board of directors granted an option to purchase 13,440 shares of our common stock to each of our non-employee directors and an option to purchase 160,000 shares of our common stock to each named executive officer and to our Chief Medical Officer. The option granted to each non-employee director will vest as to 100% of the shares underlying the stock option on the earlier of the one-year anniversary of the date of grant and the next annual meeting of our shareholders that follows the date of grant, subject to the director’s continued service on the board of directors through the vesting date. The option granted to each named executive officer

and Chief Medical Officer will vest as to 25% of the shares underlying the stock option on the one-year anniversary of the date of grant and as to the remaining 75% of the shares underlying the stock option in 36 equal monthly installments thereafter, generally subject to the employee’s continued service through the applicable vesting date.

Investment In Joint Venture

6 Months Ended

Jun. 30, 2021

Equity Method Investments and Joint Ventures [Abstract]

INVESTMENT IN JOINT VENTURE

6. INVESTMENT IN JOINT VENTURE

Rallybio Holdings, through one of its wholly-owned subsidiaries, has a 50% interest of the joint venture entity, RE Ventures I, LLC, a limited liability corporation (“REV-I”). For the three months ended June 30, 2021 and 2020, Rallybio Holdings funded $1.5 million and $1.0 million, respectively, associated with development costs. For the six months ended June 30, 2021, Rallybio Holdings funded $2.0 million, associated with development costs and for the six months ended June 30, 2020, Rallybio Holdings funded $1.6 million, associated with development costs, including $0.6 million related to the initial investment in REV-I, that was included in accrued expenses on the consolidated balance sheets as of December 31, 2019. Rallybio Holdings did not provide any additional financial support outside of capital contributions to REV-I during the three and six months ended June 30, 2021 and 2020. Rallybio Holdings held a 50% interest in the joint venture as of June 30, 2021. As of June 30, 2021, based on management’s analysis, Rallybio Holdings is not the primary beneficiary of REV-1 and accordingly, the entity is not consolidated in Rallybio Holdings financial statements.

During the three months ended June 30, 2021 and 2020, Rallybio Holdings recorded its allocable share of REV-I’s losses, which totaled $0.5 million and $0.3 million, respectively and $1.0 million and $0.5 million during the six months ended June 30, 2021 and 2020, respectively, as a loss on investment in joint venture within the condensed consolidated statements of operations and comprehensive loss. After recognition of its share of losses for the period, the carrying value and maximum exposure to risk of the REV-I investment as of June 30, 2021 and December 31, 2020, was $1.4 million and $0.3 million, respectively, which was recorded in investment in joint venture in the accompanying condensed consolidated balance sheets.

Commitments and Contingencies

6 Months Ended

Jun. 30, 2021

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

7. COMMITMENTS AND CONTINGENCIES

Purchase Commitments—Rallybio Holdings enters contracts in the normal course of business with contract research organizations and other third-party vendors for clinical trials and testing and manufacturing services. These contracts generally do not contain minimum purchase commitments and are cancellable by us upon written notice. Payments that may be due upon cancellation consist of payments for services provided or expenses incurred prior to cancellation. As of June 30, 2021 and December 31, 2020 there were no amounts accrued related to termination charges.

Lease Commitments— In June 2019, Rallybio Holdings entered into a six-year lease to occupy office space located in New Haven, Connecticut, with the option to extend the initial term of the lease for one additional five year term. Pursuant to the lease Rallybio Holdings was obligated to pay for its share of costs related to the build-out of new space. All costs associated with the build-out of the new space have been capitalized as leasehold improvements and are being amortized over the life of the lease. In October 2020, Rallybio Holdings modified the existing New Haven lease agreement and leased additional space that coincides with the original lease term expiration date.

There have been no significant changes to the disclosure of payments we have committed to make under our contractual obligations as summarized in our audited consolidated financial statements and related notes included in the IPO Prospectus.

Net Loss Per Common Unit

6 Months Ended

Jun. 30, 2021

Earnings Per Share [Abstract]

NET LOSS PER COMMON UNIT

8. NET LOSS PER COMMON UNIT

Basic and diluted loss per common unit were calculated as follows:


	THREE MONTHS ENDED JUNE 30,						SIX MONTHS ENDED JUNE 30,
NET LOSS PER COMMON UNIT (in thousands except unit and per unit amounts)	2021			2020			2021			2020
Net loss	$	(11,127	)	$	(4,893	)	$	(24,402	)	$	(8,774	)
Net loss attributable to common units-basic and diluted		(11,127	)		(4,893	)		(24,402	)		(8,774	)
Weighted average number of common units outstanding, basic and diluted		3,978,054			2,643,750			3,603,193			2,304,385
Net loss per common unit	$	(2.80	)	$	(1.85	)	$	(6.77	)	$	(3.81	)

The following common stock equivalents have been excluded from the calculations of diluted loss per common unit because their inclusion would have been antidilutive:


	THREE MONTHS ENDED JUNE 30,				SIX MONTHS ENDED JUNE 30,
ANTIDILUTIVE UNITS	2021		2020		2021		2020
Unvested restricted common units		1,518,750		2,887,500		1,518,750		2,887,500
Incentive units		20,869,704		1,858,000		20,869,704		1,858,000
Series A Preferred Units, as converted		33,478,255		33,478,255		33,478,255		33,478,255
Series B Preferred Units, as converted		104,442,965		104,442,965		104,442,965		104,442,965
Total		160,309,674		142,666,720		160,309,674		142,666,720

Subsequent Events

6 Months Ended

Jun. 30, 2021

Subsequent Events [Abstract]

Subsequent Events

9. SUBSEQUENT EVENTS

The Company evaluated all material subsequent events through the date the condensed consolidated financial statements of Rallybio Holdings were available to be issued. The Company noted the following material events occurred subsequent to June 30, 2021.

The Company completed the Reorganization. See Note 1.

In August 2021, the Company completed its IPO. See Note 1.

Summary of Significant Accounting Policies Basis of Presentation and Principles of Consolidation (Policies)	6 Months Ended
	Jun. 30, 2021
Accounting Policies [Abstract]
Unaudited Financial Information	Unaudited Financial Information— The unaudited condensed consolidated financial statements of Rallybio Holdings have been prepared in conformity with accounting principles generally accepted in the United States of America ("GAAP"), and pursuant to the rules and regulations of the Securities and Exchange Commission (the "SEC"). In the opinion of Rallybio Holdings, the information furnished reflects all adjustments, all of which are of a normal and recurring nature, necessary for a fair presentation of the financial position and results of operations for the reported interim periods. Rallybio Holdings considers events or transactions that occur after the balance sheet date but before the financial statements are issued to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. The results of operations for interim periods are not necessarily indicative of results to be expected for the full year or any other interim period. Rallybio Holdings reviews new accounting standards as issued. As of June 30, 2021 Rallybio Holdings has not identified any new standards that it believes will have a significant impact on the financial statements of Rallybio Holdings. However, Rallybio Holdings is still evaluating the impact of adopting ASU 2016-02, Leases on its condensed consolidated financial statements. There were no changes to significant accounting policies of Rallybio Holdings during the six months ended June 30, 2021 other than noted below. These accompanying unaudited condensed consolidated financial statements and notes should be read in conjunction with the audited consolidated financial statements for the year ended December 31, 2020 and notes thereto contained in the Company’s final prospectus for its IPO filed with the SEC on July 30, 2021 pursuant to Rule 424(b)(4) under the Securities Act of 1933, as amended (the “IPO Prospectus”)
Deferred Offering Costs	Deferred Offering Costs—Rallybio Holdings capitalizes incremental legal, professional accounting and other third-party fees that are directly associated with the IPO as other current assets until the IPO is consummated. After consummation of the IPO, these costs will be recorded as a reduction of additional paid-in-capital generated as a result of the offering. As of June 30, 2021, there were deferred offering costs of approximately $2.4 million included in prepaid expenses and other assets. The IPO was completed in August of 2021 and all deferred offering costs were subsequently recorded within stockholder's equity of the Corporation as a reduction of additional paid-in-capital generated from the offering.

Accrued Expenses (Tables)

6 Months Ended

Jun. 30, 2021

Accrued Liabilities, Current [Abstract]

Schedule of Accrued Expenses

Accrued expenses consisted of the following as of June 30, 2021 and December 31, 2020:


(in thousands)	JUNE 30, 2021		DECEMBER 31, 2020
Professional fees	$	1,628	$	185
Research and development		1,423		1,065
Employee expenses		1,321		1,912
Other		414		112
Asset purchase obligation		—		990
	$	4,786	$	4,264

Members' Deficit (Tables)

6 Months Ended

Jun. 30, 2021

Share-based Payment Arrangement [Abstract]

Summary of Assumptions of Fair Value of Option Pricing Granted

The assumptions that went into the option pricing models for determining the fair value of Rallybio Holdings incentive units granted for the six months ended June 30, 2021 and 2020 are as follows:


	SIX MONTHS ENDED JUNE 30,
	2021		2020
Expected volatility	71.7% - 99.5%			95.0	%
Expected term (years)	0.58 - 1.00			1.50
Risk free interest rate	0.04% - 0.10%			0.16	%
Expected dividend yield		—		—
Fair value of underlying common units	$0.47 - $1.91		$	0.44

Summary of Incentive Units Activity

The following table provides a summary of the activity for the six months ended June 30, 2021 under the 2018 Share Plan for incentive units granted to employees:


	INCENTIVE UNITS		WEIGHTED AVERAGE GRANT DATE FAIR VALUE
Outstanding at December 31, 2020		6,865,704	$	0.41
Granted		14,004,000	$	0.41
Forfeited		—
Outstanding at June 30, 2021		20,869,704	$	0.41

Summary of Equity-based Compensation


	THREE MONTHS ENDED JUNE 30,				SIX MONTHS ENDED JUNE 30,
(in thousands)	2021		2020		2021		2020
Research and Development	$	193	$	37	$	354	$	60
General and Administrative		346		57		707		139
	$	539	$	94	$	1,061	$	199

Net Loss Per Common Unit (Tables)

6 Months Ended

Jun. 30, 2021

Earnings Per Share [Abstract]

Summary of Basic and Diluted Loss Per Common Unit

Basic and diluted loss per common unit were calculated as follows:


	THREE MONTHS ENDED JUNE 30,						SIX MONTHS ENDED JUNE 30,
NET LOSS PER COMMON UNIT (in thousands except unit and per unit amounts)	2021			2020			2021			2020
Net loss	$	(11,127	)	$	(4,893	)	$	(24,402	)	$	(8,774	)
Net loss attributable to common units-basic and diluted		(11,127	)		(4,893	)		(24,402	)		(8,774	)
Weighted average number of common units outstanding, basic and diluted		3,978,054			2,643,750			3,603,193			2,304,385
Net loss per common unit	$	(2.80	)	$	(1.85	)	$	(6.77	)	$	(3.81	)

Summary of Common Stock Equivalents Excluded from Calculations of Diluted Loss Per Common Unit

The following common stock equivalents have been excluded from the calculations of diluted loss per common unit because their inclusion would have been antidilutive:


	THREE MONTHS ENDED JUNE 30,				SIX MONTHS ENDED JUNE 30,
ANTIDILUTIVE UNITS	2021		2020		2021		2020
Unvested restricted common units		1,518,750		2,887,500		1,518,750		2,887,500
Incentive units		20,869,704		1,858,000		20,869,704		1,858,000
Series A Preferred Units, as converted		33,478,255		33,478,255		33,478,255		33,478,255
Series B Preferred Units, as converted		104,442,965		104,442,965		104,442,965		104,442,965
Total		160,309,674		142,666,720		160,309,674		142,666,720

Business and Liquidity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended
	Aug. 31, 2021	Jun. 30, 2021	Dec. 31, 2020
Cash and cash equivalents		$ 112,729	$ 140,233
Shares issued price per share		$ 2.08542
IPO [Member] \| Subsequent Events [Member]
Share issued	7,130,000
Shares issued price per share	$ 13.00
Proceeds from Issuance of Common Stock	$ 92,700
Net proceeds	$ 83,200
Over-Allotment Option [Member] \| Subsequent Events [Member]
Share issued	930,000

Summary of Significant Accounting Policies Basis of Presentation and Principles of Consolidation (Additional Information) (Details) $ in Millions	Jun. 30, 2021 USD ($)
Accounting Policies [Abstract]
Deferred offering costs	$ 2.4

Accrued Expenses - Schedule Of Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Accrued Liabilities, Current [Abstract]
Professional fees	$ 1,628	$ 185
Research and development	1,423	1,065
Employee expenses	1,321	1,912
Other	414	112
Asset purchase obligation		990
Accrued expenses	$ 4,786	$ 4,264

Redeemable Convertible Preferred Units - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended				3 Months Ended		6 Months Ended		12 Months Ended
	Apr. 01, 2020	Aug. 31, 2021	Apr. 30, 2020	Mar. 31, 2020	Apr. 30, 2018	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2019	Dec. 31, 2020	May 31, 2020
Class of Stock [Line Items]
Shares issued price per share						$ 2.08542		$ 2.08542
Stock issued during period, value, conversion of units								$ 50.0
Preferred stock, dividend rate, percentage								8.00%
Preferred stock, dividends						$ 0.0	$ 0.0	$ 0.0	$ 0.0
Series A Agreement [Member]
Class of Stock [Line Items]
Aggregate purchase price of preferred stock					$ 37.0
Series B Agreement [Member]
Class of Stock [Line Items]
Aggregate purchase price of preferred stock			$ 145.2	$ 91.1
Series A-1 Redeemable Convertible Preferred Units [Member]
Class of Stock [Line Items]
Convertible redeemable preferred stock shares issued					5,549,999
Proceeds from issuance of redeemable convertible preferred stock					$ 5.5
Series A-1 Redeemable Convertible Preferred Units [Member] \| Founder [Member]
Class of Stock [Line Items]
Convertible redeemable preferred stock shares issued					450,000
Capital contribution of convertible debt					$ 0.5
Series A-1 Redeemable Convertible Preferred Units [Member] \| Series A Agreement [Member]
Class of Stock [Line Items]
Preferred stock, shares issued					5,999,999
Preferred stock par value					$ 1.00
Series A-2 Redeemable Convertible Preferred Units [Member]
Class of Stock [Line Items]
Convertible redeemable preferred stock shares issued										27,478,256
Proceeds from issuance of redeemable convertible preferred stock										$ 31.6
Series A-2 Redeemable Convertible Preferred Units [Member] \| Series A Agreement [Member]
Class of Stock [Line Items]
Preferred stock, shares issued					26,956,516
Preferred stock par value					$ 1.15
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Convertible redeemable preferred stock shares issued						104,442,965		104,442,965			104,442,965
Series B Preferred Stock [Member] \| Subsequent Event [Member]
Class of Stock [Line Items]
Stock issued during period, shares, new issues		16,402,235
Series B Redeemable Convertible Preferred Units [Member] \| Series B Agreement [Member]
Class of Stock [Line Items]
Preferred stock, shares issued			104,442,965	61,457,763
Preferred stock par value			$ 1.39028	$ 1.48
Convertible redeemable preferred stock shares issued												4,200,000
Proceeds from issuance of redeemable convertible preferred stock	$ 6.0			$ 85.1
Series A-1 and A-2 Redeemable Convertible Preferred Unit [Member] \| Subsequent Event [Member]
Class of Stock [Line Items]
Stock issued during period, shares, new issues		5,257,590

Members' Deficit - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 31, 2021	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common units, authorized		165,393,580		165,393,580		161,393,580
Common units issued							4,500,000
Vesting period							4 years
Common units reserved for issuance			137,921,220		137,921,220
Common units granted				0			4,500,000
Common units forfeited				0
Fair value of underlying common units							$ 0.15
Incentive units outstanding and expected to vest							3,375,000
Total stock-based compensation		$ 539,000	$ 94,000	$ 1,061,000	$ 199,000
2021 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting description	the board of directors granted an option to purchase 13,440 shares of our common stock to each of our non-employee directors and an option to purchase 160,000 shares of our common stock to each named executive officer and to our Chief Medical Officer. The option granted to each non-employee director will vest as to 100% of the shares underlying the stock option on the earlier of the one-year anniversary of the date of grant and the next annual meeting of our shareholders that follows the date of grant, subject to the director’s continued service on the board of directors through the vesting date. The option granted to each named executive officer and Chief Medical Officer will vest as to 25% of the shares underlying the stock option on the one-year anniversary of the date of grant and as to the remaining 75% of the shares underlying the stock option in 36 equal monthly installments thereafter, generally subject to the employee’s continued service through the applicable vesting date.
Officers and Employees \| 2018 Share Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common units reserved for issuance		22,972,360		22,972,360		18,972,360
Employees \| 2021 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common units reserved for issuance	5,440,344
Vesting percentage	75.00%
Employees \| 2021 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common units reserved for issuance	291,324
Non Employee Director [Member] \| 2021 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common units granted	13,440
Vesting percentage	100.00%
Executive Officer And Chief Medical Officer [Member] \| 2021 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common units granted	160,000
Vesting percentage	25.00%
Incentive Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available to be issued		902,656		902,656
Vesting period				4 years
Fair value of underlying common units					$ 0.44
Total stock-based compensation		$ 497,015	$ 38,620	$ 976,791	$ 73,208
Incentive Units \| 2018 Share Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available to be issued		22,972,360		22,972,360		18,972,360
Incentive units vested		2,181,052		2,181,052		495,182
Common units granted				14,004,000
Common units forfeited				0
Incentive units outstanding and expected to vest		20,869,704		20,869,704		6,865,704
Incentive Units \| Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common units granted		935,000	225,000	14,004,000	225,000
Fair value of underlying common units		$ 1.53	$ 0.40	$ 0.41	$ 0.40
Restricted Common Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common units issued							1,200,000
Vesting rights							Restricted common units issued to the founders were to vest 25% upon the 1-year anniversary of Rallybio Holdings initiating a clinical program through one of its controlled subsidiaries, and monthly thereafter over the next 36 months.
Common units granted							1,200,000
Restricted common units granted				0
Restricted common units forfeited				0
Restricted common units fully vested				3,656,250		2,812,500
Restricted units unvested		843,750		843,750		1,687,500
Weighted average fair value of restricted common units							$ 0.15
Total stock-based compensation		$ 31,641	$ 31,641	$ 63,281	$ 63,281
Restricted Common Units \| 2018 Share Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common units issued							1,200,000
Restricted common units fully vested				525,000		375,000
Restricted units unvested		675,000		675,000		825,000
Total stock-based compensation		$ 10,461	$ 23,630	$ 20,923	$ 62,132

Members' Deficit - Summary of Assumptions of Fair Value of Option Pricing Granted (Details) - $ / shares	6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of underlying common units			$ 0.15
Incentive Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, minimum	71.70%
Expected volatility		95.00%
Expected volatility, maximum	99.50%
Expected term (years)		1 year 6 months
Risk-free interest rate, minimum	0.04%
Risk-free interest rate		0.16%
Risk-free interest rate, maximum	0.10%
Fair value of underlying common units		$ 0.44
Maximum \| Incentive Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (years)	1 year
Fair value of underlying common units	$ 1.91
Minimum \| Incentive Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (years)	6 months 29 days
Fair value of underlying common units	$ 0.47

Members' Deficit - Summary of Incentive Units Activity (Details) - $ / shares	6 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Granted	0	4,500,000
Forfeited	0
2018 Share Plan \| Incentive Units
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, beginning balance	6,865,704
Granted	14,004,000
Forfeited	0
Outstanding, ending balance	20,869,704
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted average grant date fair value, beginning balance	$ 0.41
Weighted average grant date fair value, granted	0.41
Weighted average grant date fair value, ending balance	$ 0.41

Members' Deficit - Summary of Equity-based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	$ 539	$ 94	$ 1,061	$ 199
Research and Development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	193	37	354	60
General and Administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation	$ 346	$ 57	$ 707	$ 139

Investment In Joint Venture - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Joint venture investment payments	$ 1,500	$ 1,000	$ 2,000	$ 1,600
Allocable share of losses recorded	(468)	(335)	(950)	(483)
Investment in joint venture	1,360		$ 1,360		$ 310
RE Ventures I, LLC
Schedule of Equity Method Investments [Line Items]
Percentage of interest of joint venture entity			50.00%
Allocable share of losses recorded	500	$ 300	$ 1,000	$ 500
Investment in joint venture	$ 1,400		$ 1,400		$ 300
RE Ventures I, LLC \| Accrued Expenses
Schedule of Equity Method Investments [Line Items]
Initial Investment in Joint Venture						$ 600

Commitments and Contingencies (Additional Information) (Details) - USD ($)	6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2019	Dec. 31, 2020
Other Commitments [Line Items]
Termination charges	$ 0		$ 0
Lease Commitments [Member]
Other Commitments [Line Items]
Lessee, operating lease, renewal term		5 years
Lessee, operating lease, option to extend		In June 2019, Rallybio Holdings entered into a six-year lease to occupy office space located in New Haven, Connecticut, with the option to extend the initial term of the lease for one additional five year term. Pursuant to the lease Rallybio Holdings was obligated to pay for its share of costs related to the build-out of new space. All costs associated with the build-out of the new space have been capitalized as leasehold improvements and are being amortized over the life of the lease. In October 2020, Rallybio Holdings modified the existing New Haven lease agreement and leased additional space that coincides with the original lease term expiration date.
Office Building [Member]
Other Commitments [Line Items]
Lessee, operating lease, term of contract		6 years

Net Loss Per Common Unit - Summary of Basic and diluted loss per common unit (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share [Abstract]
Net loss	$ (11,127)	$ (4,893)	$ (24,402)	$ (8,774)
Net loss attributable to common units-basic and diluted	$ 11,127	$ 4,893	$ 24,402	$ 8,774
Weighted average common units outstanding, basic and diluted	3,978,054	2,643,750	3,603,193	2,304,385
Net loss per common unit	$ (2.80)	$ (1.85)	$ (6.77)	$ (3.81)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

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+ Details

Net Loss Per Common Unit - Summary of Common Stock Equivalents Excluded from Calculations of Diluted Loss Per Common Unit (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	160,309,674	142,666,720	160,309,674	142,666,720
Unvested Restricted Common Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	1,518,750	2,887,500	1,518,750	2,887,500
Incentive Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	20,869,704	1,858,000	20,869,704	1,858,000
Series A Preferred Units, as Converted
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	33,478,255	33,478,255	33,478,255	33,478,255
Series B Preferred Units, as Converted
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	104,442,965	104,442,965	104,442,965	104,442,965