Organization and Operations	6 Months Ended
Jun. 30, 2026
Organization, Consolidation and Presentation of Financial Statements [Abstract]
ORGANIZATION AND OPERATIONS	1. ORGANIZATION AND OPERATIONS Business Faeth Therapeutics, Inc. (formerly known as Sensei Biotherapeutics, Inc.) (the "Company"), a clinical-stage biotechnology company, was originally incorporated in Maryland in 1999 and subsequently reincorporated in Delaware on December 1, 2017. On February 17, 2026, the Company acquired Faeth Holdings Therapeutics, Inc. ("Faeth HoldCo") and its wholly owned subsidiary Faeth Therapeutics, LLC ("Faeth Subsidiary" and, together with Faeth HoldCo, "Legacy Faeth") pursuant to an Agreement and Plan of Merger (the "Merger Agreement"), dated as of February 17, 2026, by and among the Company, its merger subsidiaries and Legacy Faeth (such transaction, the "Acquisition"). Effective June 15, 2026, the Company changed its name from Sensei Biotherapeutics, Inc. to Faeth Therapeutics, Inc. The Company is focused on improving outcomes for cancer patients through multi-node inhibition of critical oncogenic pathways. Liquidity and capital resources Since its inception, the Company has devoted substantially all of its resources to advancing development of its portfolio of programs, establishing and protecting its intellectual property, conducting research and development activities, organizing and staffing the Company, business planning, raising capital and providing general and administrative support for these operations. The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry including, but not limited to, technical risks associated with the successful research, development and manufacturing of product candidates, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations and the ability to secure additional capital to fund operations. Current and future programs will require significant research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure. Even if the Company’s drug development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. Since its inception, the Company has incurred substantial losses and had a net loss of $186.2 million for the six months ended June 30, 2026. As of June 30, 2026, the Company had an accumulated deficit of $469.4 million. The Company expects to generate operating losses and negative operating cash flows for the foreseeable future. The Company will need additional financing to support its continuing operations and pursue its current strategy. Until such time as the Company can generate significant revenue from product sales, if ever, it expects to finance its operations through a combination of equity offerings, debt financings, collaborations, strategic alliances and licensing arrangements. The Company may be unable to raise additional funds or enter into such other agreements when needed on favorable terms or at all. The inability to raise capital as and when needed would have a negative impact on the Company’s financial condition and its ability to pursue its business strategy. The Company will need to generate significant revenue to achieve profitability, and it may never do so. The Company expects that its cash, cash equivalents and marketable securities as of June 30, 2026 of $186.4 million will be sufficient to fund its operations for at least the next twelve months from the date of issuance of these financial statements. In February 2026, the Company completed a private placement financing through the sale of Series B Non-Voting Redeemable Convertible Preferred Stock (the "Series B Preferred Stock"), resulting in gross proceeds of $200 million. On June 10, 2026, the Company obtained stockholder approval for the automatic conversion of its Series B Preferred Stock into Common Stock in accordance with Nasdaq listing rules. On June 15, 2026, 24,435.594 shares of Series B Preferred Stock automatically converted into an aggregate of 24,435,594 shares of Common Stock. Such converted shares were thereafter retired and, as a result, 24,435.594 shares resumed the status of authorized but unissued shares of preferred stock. Pursuant to the terms of the Certificate of Designation (as defined below), conversion is subject to beneficial ownership limitations that prevent any holder from converting shares if such conversion would result in the holder and its affiliates beneficially owning more than 9.99% of the Company’s outstanding Common Stock. As of June 30, 2026, 501.899 shares of Series B Preferred Stock remain outstanding as a result of these blocker provisions. These remaining shares will convert into shares of Common Stock from time to time as holders sell down their positions or otherwise remain below their applicable beneficial ownership limitations.

Organization and Operations

6 Months Ended

Jun. 30, 2026

Organization, Consolidation and Presentation of Financial Statements [Abstract]

1. ORGANIZATION AND OPERATIONS

Business

Faeth Therapeutics, Inc. (formerly known as Sensei Biotherapeutics, Inc.) (the "Company"), a clinical-stage biotechnology company, was originally incorporated in Maryland in 1999 and subsequently reincorporated in Delaware on December 1, 2017.

On February 17, 2026, the Company acquired Faeth Holdings Therapeutics, Inc. ("Faeth HoldCo") and its wholly owned subsidiary Faeth Therapeutics, LLC ("Faeth Subsidiary" and, together with Faeth HoldCo, "Legacy Faeth") pursuant to an Agreement and Plan of Merger (the "Merger Agreement"), dated as of February 17, 2026, by and among the Company, its merger subsidiaries and Legacy Faeth (such transaction, the "Acquisition").

Effective June 15, 2026, the Company changed its name from Sensei Biotherapeutics, Inc. to Faeth Therapeutics, Inc. The Company is focused on improving outcomes for cancer patients through multi-node inhibition of critical oncogenic pathways.

Liquidity and capital resources

Since its inception, the Company has devoted substantially all of its resources to advancing development of its portfolio of programs, establishing and protecting its intellectual property, conducting research and development activities, organizing and staffing the Company, business planning, raising capital and providing general and administrative support for these operations. The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry including, but not limited to, technical risks associated with the successful research, development and manufacturing of product candidates, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations and the ability to secure additional capital to fund operations. Current and future programs will require significant research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure. Even if the Company’s drug development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales.

Since its inception, the Company has incurred substantial losses and had a net loss of $186.2 million for the six months ended June 30, 2026. As of June 30, 2026, the Company had an accumulated deficit of $469.4 million. The Company expects to generate operating losses and negative operating cash flows for the foreseeable future.

The Company will need additional financing to support its continuing operations and pursue its current strategy. Until such time as the Company can generate significant revenue from product sales, if ever, it expects to finance its operations through a combination of equity offerings, debt financings, collaborations, strategic alliances and licensing arrangements. The Company may be unable to raise additional funds or enter into such other agreements when needed on favorable terms or at all. The inability to raise capital as and when needed would have a negative impact on the Company’s financial condition and its ability to pursue its business strategy. The Company will need to generate significant revenue to achieve profitability, and it may never do so.

The Company expects that its cash, cash equivalents and marketable securities as of June 30, 2026 of $186.4 million will be sufficient to fund its operations for at least the next twelve months from the date of issuance of these financial statements. In February 2026, the Company completed a private placement financing through the sale of Series B Non-Voting Redeemable Convertible Preferred Stock (the "Series B Preferred Stock"), resulting in gross proceeds of $200 million.

On June 10, 2026, the Company obtained stockholder approval for the automatic conversion of its Series B Preferred Stock into Common Stock in accordance with Nasdaq listing rules. On June 15, 2026, 24,435.594 shares of Series B Preferred Stock automatically converted into an aggregate of 24,435,594 shares of Common Stock. Such converted shares were thereafter retired and, as a result, 24,435.594 shares resumed the status of authorized but unissued shares of preferred stock.

Pursuant to the terms of the Certificate of Designation (as defined below), conversion is subject to beneficial ownership limitations that prevent any holder from converting shares if such conversion would result in the holder and its affiliates beneficially owning more than 9.99% of the Company’s outstanding Common Stock. As of June 30, 2026, 501.899 shares of Series B Preferred Stock remain outstanding as a result of these blocker provisions. These remaining shares will convert into shares of Common Stock from time to time as holders sell down their positions or otherwise remain below their applicable beneficial ownership limitations.