COLLABORATION AND LICENSE AGREEMENTS	6 Months Ended
Jun. 30, 2025
License and Collaboration Agreements [Abstract]
COLLABORATION AND LICENSE AGREEMENTS	COLLABORATION AND LICENSE AGREEMENTS` In April 2024, the Company entered into a two-year collaboration agreement (the "J&J Collaboration Agreement"), with Johnson & Johnson through its wholly-owned subsidiary, Momenta Pharmaceuticals, Inc. (“J&J”) to facilitate the advancement of research into products to address unmet needs relating to FNAIT. In April 2025, the Company announced that RLYB212 Phase 2 pharmacokinetic results did not achieve target concentrations, including the minimum target concentration required for efficacy, and that the Company would discontinue its RLYB212 program for the prevention of FNAIT. The Company will continue to follow any previously screened Phase 2 participant who was also eligible to enroll in the multinational FNAIT natural history study, in accordance with the study's protocol. A total of 14,300 pregnant women of different racial and ethnic characteristics in North America and Europe were screened in the FNAIT natural history study, and two are currently enrolled, including the participant from the Phase 2 trial. Pursuant to the J&J Collaboration Agreement, the Company received an upfront payment of $0.5 million from J&J for the information dissemination and data provision services under the agreement. The J&J Collaboration Agreement provides that the Company is eligible for payments upon the achievement of certain screening-related events, however, the Company has discontinued screening and enrollment in both the FNAIT natural history study and the RLYB212 Phase 2 clinical trial. The Company evaluated the agreement and determined it was within the scope of ASC 606, Revenue Recognition ("ASC 606"). The Company determined there were performance obligations as follows: (1) Data collection and submission revenue – derived from Rallybio’s ongoing management of the studies including the maintenance of a minimum site footprint, the license to utilize, and timely, semi-annual submission of the anonymized data, in the required formats. (2) Dissemination of J&J materials & participant revenue – derived from Rallybio’s dissemination of content, information or materials related to the J&J-Sponsored Studies that are developed by J&J and are provided by Rallybio for the purpose of disseminating such content, information, or materials to staff at Rallybio study sites to provide to potential eligible participants regarding J&J’s independent study. In April 2024, the Company also entered into the JJDC Securities Purchase Agreement. Under the terms of the JJDC Securities Purchase Agreement, JJDC purchased 3,636,363 shares of the Company's common stock with a par value of $0.0001 per share for a share purchase price of $1.82 per share which included a 10% premium on the then-current market price, for an aggregate purchase price of $6.6 million. The JJDC Securities Purchase Agreement contains provisions related to the registration of the shares and the restriction on the sale or transfer of the shares for a period of time. The Company determined the J&J Collaboration Agreement and the JJDC Securities Purchase Agreement represented combined agreements. In accordance with ASC 606 and ASC Topic 820, Fair Value Measurement, total consideration of $1.2 million for the shares of common stock from the JJDC Securities Purchase Agreement, which represents the premium of $0.7 million and discount for lack of marketability of $0.5 million, has been allocated to revenue and will be recognized over the two year expected performance period. The Company valued the common stock issued to JJDC, in connection with the JJDC Securities Purchase Agreement at fair value. The resulting fair value of $5.4 million was determined by applying the discount due to lack of marketability during the registration and lock-up period to the public trading price of the common stock, which is a Level 1 input, on the date of sale. The Company determined the value of the lack of marketability during the registration and lock-up period by utilizing put option models, which are considered Level 3 inputs. Such option models included the Company’s historical volatility of 113.2% and the risk-free rate of 5.28% based on U.S. Treasury bond rates, as key inputs. The Company recognized revenue of $0.2 million and $0.4 million during the three and six months ended June 30, 2025, respectively, and $0.3 million for both the three and six months ended June 30, 2024, related to data collection and data submission with the identified performance obligations, and the premium and discount allocated to revenue from the sale of the common stock to JJDC. The remaining revenue is included in deferred revenue on the Company's condensed consolidated balance sheets as of June 30, 2025, and will be recognized as the performance obligations are satisfied. The Company determined that the J&J Collaboration Agreement is not in the scope of ASC 808, Collaborative Arrangements.

In April 2024, the Company entered into a two-year collaboration agreement (the "J&J Collaboration Agreement"), with Johnson & Johnson through its wholly-owned subsidiary, Momenta Pharmaceuticals, Inc. (“J&J”) to facilitate the advancement of research into products to address unmet needs relating to FNAIT.

In April 2025, the Company announced that RLYB212 Phase 2 pharmacokinetic results did not achieve target concentrations, including the minimum target concentration required for efficacy, and that the Company would discontinue its RLYB212 program for the prevention of FNAIT. The Company will continue to follow any previously screened Phase 2 participant who was also eligible to enroll in the multinational FNAIT natural history study, in accordance with the study's protocol. A total of 14,300 pregnant women of different racial and ethnic characteristics in North America and Europe were screened in the FNAIT natural history study, and two are currently enrolled, including the participant from the Phase 2 trial.

Pursuant to the J&J Collaboration Agreement, the Company received an upfront payment of $0.5 million from J&J for the information dissemination and data provision services under the agreement. The J&J Collaboration Agreement provides that the Company is eligible for payments upon the achievement of certain screening-related events, however, the Company has discontinued screening and enrollment in both the FNAIT natural history study and the RLYB212 Phase 2 clinical trial.

(1) Data collection and submission revenue – derived from Rallybio’s ongoing management of the studies including the maintenance of a minimum site footprint, the license to utilize, and timely, semi-annual submission of the anonymized data, in the required formats.

(2) Dissemination of J&J materials & participant revenue – derived from Rallybio’s dissemination of content, information or materials related to the J&J-Sponsored Studies that are developed by J&J and are provided by Rallybio for the purpose of disseminating such content, information, or materials to staff at Rallybio study sites to provide to potential eligible participants regarding J&J’s independent study.

In April 2024, the Company also entered into the JJDC Securities Purchase Agreement. Under the terms of the JJDC Securities Purchase Agreement, JJDC purchased 3,636,363 shares of the Company's common stock with a par value of $0.0001 per share for a share purchase price of $1.82 per share which included a 10% premium on the then-current market price, for an aggregate purchase price of $6.6 million. The JJDC Securities Purchase Agreement contains provisions related to the registration of the shares and the restriction on the sale or transfer of the shares for a period of time. The Company determined the J&J Collaboration Agreement and the JJDC Securities Purchase Agreement represented combined agreements. In accordance with ASC 606 and ASC Topic 820, Fair Value Measurement, total consideration of $1.2 million for the shares of common stock from the JJDC Securities Purchase Agreement, which represents the premium of $0.7 million and discount for lack of marketability of $0.5 million, has been allocated to revenue and will be recognized over the two year expected performance period.

The Company valued the common stock issued to JJDC, in connection with the JJDC Securities Purchase Agreement at fair value. The resulting fair value of $5.4 million was determined by applying the discount due to lack of marketability during the registration and lock-up period to the public trading price of the common stock, which is a Level 1 input, on the date of sale. The Company determined the value of the lack of marketability during the registration and lock-up period by utilizing put option models, which are considered Level 3 inputs. Such option models included the Company’s historical volatility of 113.2% and the risk-free rate of 5.28% based on U.S. Treasury bond rates, as key inputs.

The Company recognized revenue of $0.2 million and $0.4 million during the three and six months ended June 30, 2025, respectively, and $0.3 million for both the three and six months ended June 30, 2024, related to data collection and data submission with the identified performance obligations, and the premium and discount allocated to revenue from the sale of the common stock to JJDC. The remaining revenue is included in deferred revenue on the Company's condensed consolidated balance sheets as of June 30, 2025, and will be recognized as the performance obligations are satisfied.