Commitments and Contingencies	6 Months Ended
Jun. 30, 2025
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	9. Commitments and Contingencies Leases The Company's commitments under its operating leases are described in Note 8. Research and Development Agreements The Company enters into various agreements in the ordinary course of business, such as those with suppliers, contract development and manufacturing organizations, clinical research organizations, and other research and development vendors. These agreements provide for termination at the request of either party, generally with less than one year’s notice. Therefore, they are cancellable contracts and, if canceled, are not expected to have a material effect on the Company’s financial condition, results of operations, or cash flows. License and Royalty Agreements The Company is required to pay certain milestone payments contingent upon the achievement of specific development and regulatory events in accordance with the UCSD Agreement (Note 6). Through June 30, 2025, the Company achieved development milestones totaling $0.1 million, which were recorded as research and development expenses. No other milestones were achieved or probable as of June 30, 2025 and December 31, 2024. The Company is required to pay royalties on commercial sales of products developed under the UCSD Agreement. The Company’s product candidate was in clinical development as of June 30, 2025, and no such royalties were due. The Company is obligated to pay royalties to Samsara under the Royalty Agreement (Note 6). The Company recognized an initial royalty obligation liability in the amount of $32.1 million, which was based on its estimated fair value at the effective date of the Royalty Agreement. Once royalty payments to Samsara are deemed probable and estimable, and if such amounts exceed the royalty liability balance, the Company will impute interest to accrete the royalty obligation on a prospective basis based on such estimates. As of June 30, 2025, these royalties were not probable and estimable. Legal Contingencies The Company, from time to time, may be a party to litigation arising in the ordinary course of business. If the potential loss from any claim, asserted or unasserted, or legal proceeding is considered probable and the amount is reasonably estimable, the Company will accrue a liability for the estimated loss. Litigation Related to Legacy Operations of AlloVir On January 19, 2024, a purported stockholder of AlloVir filed a lawsuit, captioned Zerbato v. AlloVir, Inc. et al., No. 1:24-cv-10152 (D. Mass.) (the “Securities Class Action”), in the U.S. District Court for the District of Massachusetts (the “Court”) against AlloVir and two of its officers purportedly on behalf of a putative class of stockholders. On April 16, 2024, the Court appointed stockholders Harry Levin and Julio Maurice Bueno as lead plaintiffs and their counsel as lead counsel in the action. On June 17, 2024, lead plaintiffs filed their amended complaint. In the amended complaint, lead plaintiffs asserted claims purportedly on behalf of a putative class of stockholders consisting of persons who purchased or otherwise acquired AlloVir securities between January 11, 2023 and December 21, 2023, inclusive. The amended complaint asserted claims under Sections 10(b) and 20(a) of the Securities Exchange Act of 1934, as amended, and the related regulations, alleging that the defendants made false and misleading statements and omissions to investors relating to AlloVir’s three Phase 3 studies of posoleucel. The complaint sought, among other things, damages, prejudgment and post-judgment interest, and attorneys’ fees, expert fees and other costs. On April 14, 2025, the parties executed a definitive stipulation and agreement of settlement resolving the claims in the Securities Class Action for $1.0 million. On July 30, 2025, the Court entered an order granting final approval of the settlement and dismissing the Securities Class Action with prejudice. On October 21, 2024, a purported AlloVir stockholder filed a derivative lawsuit, captioned Lister v. Brainard et al., No. 1:24-cv-12658 (D. Mass.), in the U.S. District Court for the District of Massachusetts against certain of AlloVir’s officers and directors and naming AlloVir as a nominal defendant. The derivative complaint alleged, purportedly on behalf of AlloVir, violations of Section 14(a) of the Securities Exchange Act of 1934, breach of fiduciary duties, unjust enrichment, waste of corporate assets, gross mismanagement, and abuse of control against the individual defendants and contribution under Sections 10(b) and 21D of the Securities Exchange Act of 1934 against Dr. Brainard and Mr. Sinha. These claims were based on substantially identical allegations as the complaint in the above-listed Securities Class Action. The lawsuit sought, among other things, an award of damages and restitution in favor of AlloVir, certain changes to AlloVir’s corporate governance, and attorneys’ fees and costs. On August 1, 2025, the plaintiff filed a notice voluntarily dismissing the derivative lawsuit without prejudice. Litigation Related to the Merger Two complaints have been filed by purported AlloVir stockholders as individual actions against AlloVir and the members of its board of directors in the Supreme Court of the State of New York, New York County, captioned Keller v. AlloVir, Inc. et al., No. 650989/2025 (N.Y. Sup. Ct. Feb. 20, 2025), and Morgan v. AlloVir, Inc. et al., No. 650965/2025 (N.Y. Sup. Ct. Feb. 19, 2025) (the “Complaints”). The Complaints allege that the proxy statement/prospectus describing the transaction between Legacy Kalaris and AlloVir misrepresented and/or omitted certain purportedly material information, and assert claims for negligent misrepresentation and concealment and negligence under New York common law. The Complaints seek various remedies including, among other things, an order enjoining the consummation of the merger, requiring the defendants to file an amended proxy statement/prospectus, rescinding the merger or granting rescissory damages, and awarding costs, including plaintiff’s attorneys’ fees and experts’ fees, and other relief the court may deem just and proper. AlloVir and Legacy Kalaris deny the allegations in the Complaints and deny that any further disclosure beyond that already contained in the proxy statement/prospectus was required under applicable law. Guarantees and Indemnifications In the normal course of business, the Company enters into agreements that contain a variety of representations and provide for general indemnification. The Company’s exposure under these agreements is unknown because it involves claims that may be made against the Company in the future. To date, the Company has not paid any claims or been required to defend any action related to its indemnification obligations. As of June 30, 2025 and December 31, 2024, the Company does not have any material indemnification claims that were probable or reasonably possible.

Commitments and Contingencies

6 Months Ended

Jun. 30, 2025

Commitments and Contingencies Disclosure [Abstract]

9. Commitments and Contingencies

Leases

The Company's commitments under its operating leases are described in Note 8.

Research and Development Agreements

The Company enters into various agreements in the ordinary course of business, such as those with suppliers, contract development and manufacturing organizations, clinical research organizations, and other research and development vendors. These agreements provide for termination at the request of either party, generally with less than one year’s notice. Therefore, they are cancellable contracts and, if canceled, are not expected to have a material effect on the Company’s financial condition, results of operations, or cash flows.

License and Royalty Agreements

The Company is required to pay certain milestone payments contingent upon the achievement of specific development and regulatory events in accordance with the UCSD Agreement (Note 6). Through June 30, 2025, the Company achieved development milestones totaling $0.1 million, which were recorded as research and development expenses. No other milestones were achieved or probable as of June 30, 2025 and December 31, 2024. The Company is required to pay royalties on commercial sales of products developed under the UCSD Agreement. The Company’s product candidate was in clinical development as of June 30, 2025, and no such royalties were due.

The Company is obligated to pay royalties to Samsara under the Royalty Agreement (Note 6). The Company recognized an initial royalty obligation liability in the amount of $32.1 million, which was based on its estimated fair value at the effective date of the Royalty Agreement. Once royalty payments to Samsara are deemed probable and estimable, and if such amounts exceed the royalty liability balance, the Company will impute interest to accrete the royalty obligation on a prospective basis based on such estimates. As of June 30, 2025, these royalties were not probable and estimable.

Legal Contingencies

The Company, from time to time, may be a party to litigation arising in the ordinary course of business. If the potential loss from any claim, asserted or unasserted, or legal proceeding is considered probable and the amount is reasonably estimable, the Company will accrue a liability for the estimated loss.

Litigation Related to Legacy Operations of AlloVir

On January 19, 2024, a purported stockholder of AlloVir filed a lawsuit, captioned Zerbato v. AlloVir, Inc. et al., No. 1:24-cv-10152 (D. Mass.) (the “Securities Class Action”), in the U.S. District Court for the District of Massachusetts (the “Court”) against AlloVir and two of its officers purportedly on behalf of a putative class of stockholders. On April 16, 2024, the Court appointed stockholders Harry Levin and Julio Maurice Bueno as lead plaintiffs and their counsel as lead counsel in the action. On June 17, 2024, lead plaintiffs filed their amended complaint. In the amended complaint, lead plaintiffs asserted claims purportedly on behalf of a putative class of stockholders consisting of persons who purchased or otherwise acquired AlloVir securities between January 11, 2023 and December 21, 2023, inclusive. The amended complaint asserted claims under Sections 10(b) and 20(a) of the Securities Exchange Act of 1934, as amended, and the related regulations, alleging that the defendants made false and misleading statements and omissions to investors relating to AlloVir’s three Phase 3 studies of posoleucel. The complaint sought, among other things, damages, prejudgment and post-judgment interest, and attorneys’ fees, expert fees and other costs. On April 14, 2025, the parties executed a definitive stipulation and agreement of settlement resolving the claims in the Securities Class Action for $1.0 million. On July 30, 2025, the Court entered an order granting final approval of the settlement and dismissing the Securities Class Action with prejudice.

On October 21, 2024, a purported AlloVir stockholder filed a derivative lawsuit, captioned Lister v. Brainard et al., No. 1:24-cv-12658 (D. Mass.), in the U.S. District Court for the District of Massachusetts against certain of AlloVir’s officers and directors and naming AlloVir as a nominal defendant. The derivative complaint alleged, purportedly on behalf of AlloVir, violations of Section 14(a) of the Securities Exchange Act of 1934, breach of fiduciary duties, unjust enrichment, waste of corporate assets, gross mismanagement, and abuse of control against the individual defendants and contribution under Sections 10(b) and 21D of the Securities Exchange Act of 1934 against Dr. Brainard and Mr. Sinha. These claims were based on substantially identical allegations as the complaint in the above-listed Securities Class Action. The lawsuit sought, among other things, an award of damages and restitution in favor of AlloVir, certain changes to AlloVir’s corporate governance, and attorneys’ fees and costs. On August 1, 2025, the plaintiff filed a notice voluntarily dismissing the derivative lawsuit without prejudice.

Litigation Related to the Merger

Two complaints have been filed by purported AlloVir stockholders as individual actions against AlloVir and the members of its board of directors in the Supreme Court of the State of New York, New York County, captioned Keller v. AlloVir, Inc. et al., No. 650989/2025 (N.Y. Sup. Ct. Feb. 20, 2025), and Morgan v. AlloVir, Inc. et al., No. 650965/2025 (N.Y. Sup. Ct. Feb. 19, 2025) (the “Complaints”). The Complaints allege that the proxy statement/prospectus describing the transaction between Legacy Kalaris and AlloVir misrepresented and/or omitted certain purportedly material information, and assert claims for negligent misrepresentation and concealment and negligence under New York common law. The Complaints seek various remedies including, among other things, an order enjoining the consummation of the merger, requiring the defendants to file an amended proxy statement/prospectus, rescinding the merger or granting rescissory damages, and awarding costs, including plaintiff’s attorneys’ fees and experts’ fees, and other relief the court may deem just and proper. AlloVir and Legacy Kalaris deny the allegations in the Complaints and deny that any further disclosure beyond that already contained in the proxy statement/prospectus was required under applicable law.

Guarantees and Indemnifications

In the normal course of business, the Company enters into agreements that contain a variety of representations and provide for general indemnification. The Company’s exposure under these agreements is unknown because it involves claims that may be made against the Company in the future. To date, the Company has not paid any claims or been required to defend any action related to its indemnification obligations. As of June 30, 2025 and December 31, 2024, the Company does not have any material indemnification claims that were probable or reasonably possible.