Nature of Business and Liquidity	6 Months Ended
Jun. 30, 2026
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business and Liquidity	1. NATURE OF BUSINESS AND Liquidity MBX Biosciences, Inc. (“MBX” or the “Company”) is a clinical-stage biopharmaceutical company focused on the discovery and development of novel precision peptide therapies for the treatment of endocrine and metabolic disorders. The Company is advancing a pipeline of novel candidates for endocrine and metabolic disorders. The Company was organized in August 2018 in Indiana as a Limited Liability Company and converted to a C corporation in the state of Delaware in April 2019. The Company maintains its corporate offices in Carmel, Indiana, as well as lab and supplemental office space in Burlington, Massachusetts. Since inception, the Company has devoted substantially all of its resources to drug discovery and development of its product candidates canvuparatide (MBX 2109), imapextide (MBX 1416), MBX 4291, and other preclinical programs, building an intellectual property portfolio, organizing and staffing the Company, business planning, raising capital and providing general and administrative support for these operations. The Company does not have any products approved for sale and has not generated any revenue from product sales. The Company has historically funded its operations primarily through the issuance and sale of our common stock, including through our initial public offering (the "IPO"), convertible preferred stock and convertible notes, which generated approximately $401.8 million in aggregate gross proceeds. In September 2025, the Company also completed an underwritten public offering (the "September 2025 Offering") of 11,108,055 shares of its common stock, which generated approximately $199.9 million in aggregate gross proceeds. In February 2026, the Company sold 2,250,986 shares of its common stock under its Open Market Sale AgreementSM with Jefferies, LLC (the "February 2026 ATM Offering"), which generated approximately $87.1 million in aggregate gross proceeds, resulting in $688.8 million in cumulative, aggregate gross proceeds from those sales of common stock. In March 2026, the Company filed an automatic shelf registration statement with the Securities and Exchange Commission (File No. 333-294237) and increased the amount available under the Open Market Sale AgreementSM with Jefferies, LLC (the "March 2026 Sales Agreement"), under which the Company may now, from time to time in one or more offerings, sell and issue shares of its common stock having an aggregate price of up to $250.0 million. Liquidity From inception and through June 30, 2026, the Company has devoted substantially all of its efforts to drug discovery and development. The Company has a limited operating history, has incurred operating losses since inception and expects to continue to incur significant operating losses for the foreseeable future. The Company incurred net losses of $60.6 million and $87.0 million for the six months ended June 30, 2026 and the year ended December 31, 2025, respectively. As of June 30, 2026, the Company has an accumulated deficit of $285.1 million and cash, cash equivalents and marketable securities of $418.6 million. Based on the Company’s current operating plan, management believes that existing cash and cash equivalents and marketable securities will be sufficient to fund the Company’s obligations for at least 12 months from the date of issuance of these condensed financial statements. Basis of presentation The accompanying unaudited condensed financial statements as of June 30, 2026 and for the three and six months ended June 30, 2026 and 2025 have been prepared in accordance with U.S. generally accepted accounting principles ("U.S. GAAP") for interim financial information and pursuant to Article 10 of Regulation S-X of the Securities Act of 1933, as amended. Accordingly, they do not include all of the information and notes required by U.S. GAAP for complete financial statements. These unaudited condensed financial statements include only normal and recurring adjustments that the Company believes are necessary to fairly state the Company’s financial position and the results of its operations and cash flows. The results for the three and six months ended June 30, 2026 are not necessarily indicative of the results expected for the full fiscal year or any subsequent interim period. The condensed balance sheet at December 31, 2025 has been derived from the audited financial statements at that date but does not include all disclosures required by U.S. GAAP for complete financial statements. Because all of the disclosures required by U.S. GAAP for complete financial statements are not included herein, these unaudited condensed financial statements and the notes accompanying them should be read in conjunction with the Company’s audited financial statements for the year ended December 31, 2025 included in the Company's Annual Report on Form 10-K as filed with the SEC on March 12, 2026 ("2025 Annual Report").

MBX Biosciences, Inc. (“MBX” or the “Company”) is a clinical-stage biopharmaceutical company focused on the discovery and development of novel precision peptide therapies for the treatment of endocrine and metabolic disorders. The Company is advancing a pipeline of novel candidates for endocrine and metabolic disorders. The Company was organized in August 2018 in Indiana as a Limited Liability Company and converted to a C corporation in the state of Delaware in April 2019. The Company maintains its corporate offices in Carmel, Indiana, as well as lab and supplemental office space in Burlington, Massachusetts.

Since inception, the Company has devoted substantially all of its resources to drug discovery and development of its product candidates canvuparatide (MBX 2109), imapextide (MBX 1416), MBX 4291, and other preclinical programs, building an intellectual property portfolio, organizing and staffing the Company, business planning, raising capital and providing general and administrative support for these operations. The Company does not have any products approved for sale and has not generated any revenue from product sales. The Company has historically funded its operations primarily through the issuance and sale of our common stock, including through our initial public offering (the "IPO"), convertible preferred stock and convertible notes, which generated approximately $401.8 million in aggregate gross proceeds. In September 2025, the Company also completed an underwritten public offering (the "September 2025 Offering") of 11,108,055 shares of its common stock, which generated approximately $199.9 million in aggregate gross proceeds. In February 2026, the Company sold 2,250,986 shares of its common stock under its Open Market Sale AgreementSM with Jefferies, LLC (the "February 2026 ATM Offering"), which generated approximately $87.1 million in aggregate gross proceeds, resulting in $688.8 million in cumulative, aggregate gross proceeds from those sales of common stock. In March 2026, the Company filed an automatic shelf registration statement with the Securities and Exchange Commission (File No. 333-294237) and increased the amount available under the Open Market Sale AgreementSM with Jefferies, LLC (the "March 2026 Sales Agreement"), under which the Company may now, from time to time in one or more offerings, sell and issue shares of its common stock having an aggregate price of up to $250.0 million.

Liquidity

From inception and through June 30, 2026, the Company has devoted substantially all of its efforts to drug discovery and development. The Company has a limited operating history, has incurred operating losses since inception and expects to continue to incur significant operating losses for the foreseeable future. The Company incurred net losses of $60.6 million and $87.0 million for the six months ended June 30, 2026 and the year ended December 31, 2025, respectively. As of June 30, 2026, the Company has an accumulated deficit of $285.1 million and cash, cash equivalents and marketable securities of $418.6 million. Based on the Company’s current operating plan, management believes that existing cash and cash equivalents and marketable securities will be sufficient to fund the Company’s obligations for at least 12 months from the date of issuance of these condensed financial statements.

Basis of presentation

The accompanying unaudited condensed financial statements as of June 30, 2026 and for the three and six months ended June 30, 2026 and 2025 have been prepared in accordance with U.S. generally accepted accounting principles ("U.S. GAAP") for interim financial information and pursuant to Article 10 of Regulation S-X of the Securities Act of 1933, as amended. Accordingly, they do not include all of the information and notes required by U.S. GAAP for complete financial statements. These unaudited condensed financial statements include only normal and recurring adjustments that the Company believes are necessary to fairly state the Company’s financial position and the results of its operations and cash flows. The results for the three and six months ended June 30, 2026 are not necessarily indicative of the results expected for the full fiscal year or any subsequent interim period. The condensed balance sheet at December 31, 2025 has been derived from the audited financial statements at that date but does not include all disclosures required by U.S. GAAP for complete financial statements. Because all of the disclosures required by U.S. GAAP for complete financial statements are not included herein, these unaudited condensed financial statements and the notes accompanying them should be read in conjunction with the Company’s audited financial statements for the year ended December 31, 2025 included in the Company's Annual Report on Form 10-K as filed with the SEC on March 12, 2026 ("2025 Annual Report").