Climb Bio sues Alumis and Acelyrin over $3 million budoprutug milestone payment

Climb Bio, Inc. (Nasdaq: CLYM) filed a complaint on December 31, 2025 in Delaware Superior Court against Alumis Inc. and Acelyrin, Inc. The complaint names Alumis and Acelyrin as the defendants. Acelyrin is a wholly owned subsidiary of Alumis. The company disclosed the filing in a Form 8-K filed December 31, 2025 and attached the complaint as Exhibit 99.1. The complaint names no individual defendants.

Climb asks the court for a declaratory judgment that its drug candidate, budoprutug, is not a "Product" under a 2024 asset purchase agreement. It also asks the court to declare that Climb does not owe the $3 million milestone payment that Alumis invoiced for payment by January 1, 2026. The exhibit leaves the case number blank.

The 2024 asset sale

The dispute concerns an Asset Purchase Agreement dated January 11, 2024 between Acelyrin and Tenet Medicines, Inc., a wholly owned subsidiary of Climb. The agreement originally covered Acelyrin's budoprutug assets. The complaint alleges that Tenet made an upfront payment of over $7 million for them, and that the agreement carries potential milestone and earn-out payments if a Product is developed and commercialized.

Climb's annual report on Form 10-K, filed March 25, 2025, calls budoprutug its cornerstone product candidate. It is a clinical-stage anti-CD19 monoclonal antibody that Climb says has rights worldwide for all indications except oncology. The annual report says the FDA cleared a Phase 2, dose-range-finding trial in primary membranous nephropathy in March 2025.

Climb's allegations

The complaint alleges that the agreement defines a Product as a budoprutug drug that would infringe Royalty-Bearing Patents. It says those patents are limited to patents transferred under the agreement, or certain patents filed within nine months of closing. According to the complaint, Acelyrin transferred no patents and none was filed in that window, so no Royalty-Bearing Patents exist.

The complaint also alleges that under Alumis' reading, the defendants could receive upwards of $100 million beyond the initial purchase price in the coming years, for no added value. Climb says it dosed its first patient with budoprutug in a Phase 2 trial on November 17, 2025 and sent Alumis a courtesy notice. Alumis then invoiced the $3 million payment. Climb says it made a final attempt to resolve the matter on December 17, 2025, and that Alumis reaffirmed its demand.

The complaint also says Acelyrin merged with Alumis in May 2025, and that Climb then contacted Alumis to confirm each side's rights. Alumis disagreed, according to the complaint. These are Climb's allegations, and the 8-K does not include any response from Alumis or Acelyrin.

Where the case was filed

The complaint cites Article IV, Section 7 of the Delaware Constitution as the basis for subject matter jurisdiction. It says the agreement gives exclusive jurisdiction to the U.S. District Court for the District of Delaware where federal jurisdiction exists, or to the Court of Chancery where it does not. Climb argues that neither court can hear this contract claim. It says federal jurisdiction is absent because the parties are not diverse, and that the Court of Chancery does not hear claims for legal relief. Climb asks that the case be assigned to the Superior Court's Complex Commercial Litigation Division, because the amount in controversy exceeds $1 million.

The 8-K itself is a short filing. It describes the claim and attaches the complaint, and it does not describe the company's potential exposure beyond the $3 million invoice.

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