Nature of Business and Basis of Presentation	3 Months Ended
Mar. 31, 2026
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business and Basis of Presentation	1. Nature of Business and Basis of Presentation PepGen Inc., hereinafter referred to as PepGen or the Company, is a clinical-stage biotechnology company advancing the next generation of oligonucleotide therapeutics with the goal of transforming the treatment of severe neuromuscular and neurologic diseases. The Company's principal offices are located in Boston, Massachusetts. Liquidity Since inception, the Company has not generated any revenue from product sales or other sources and has incurred significant operating losses and negative cash flows from operations. The Company’s primary uses of cash, cash equivalents, and marketable securities to date have been funding research and development activities, business planning, establishing and maintaining the Company’s intellectual property portfolio, hiring personnel, leasing premises and associated capital expenditures, raising capital, and providing general and administrative support for these operations. As of March 31, 2026, the Company had an accumulated deficit of $378.9 million. To date, the Company has funded operations primarily through private placements of convertible preferred stock, the sale of shares of common stock in its initial public offering, or IPO, the sale of shares of common stock under its At-the-Market Equity Offering Sales Agreement, or Sales Agreement, with Stifel, Nicolaus & Company, Incorporated, or Stifel, and through the sale of shares of common stock in follow-on public offerings in February 2024, referred to as the 2024 Offering, and in September 2025, referred to as the 2025 Offering. As of March 31, 2026, the Company had cash, cash equivalents, and marketable securities of $132.3 million. The Company believes that its cash, cash equivalents, and marketable securities as of March 31, 2026, will be sufficient to fund its currently planned operations for at least the next 12 months from the issuance of these condensed consolidated financial statements. As the Company continues to pursue its business plan to successfully develop and obtain regulatory approval for its product candidates, it expects to finance its operations through the sale of equity, debt financings or other capital resources, which could include income from collaborations, strategic partnerships or marketing, distribution, licensing or other strategic arrangements with third parties, or from grants. However, there can be no assurance that any additional financing or strategic transactions will be available to the Company on acceptable terms, if at all. If events or circumstances occur such that the Company does not obtain additional funding, it may need to delay, reduce or eliminate its product development or future commercialization efforts, which could have a material adverse effect on the Company’s business, results of operations or financial condition. Basis of Presentation and Consolidation The accompanying condensed consolidated financial statements are unaudited and have been prepared in conformity with generally accepted accounting principles in the United States of America, or GAAP. Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification and Accounting Standards Update of the Financial Accounting Standards Board, or FASB. The condensed consolidated financial statements have been prepared on the same basis as the audited annual financial statements. Certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. These condensed consolidated financial statements, in the opinion of management, reflect all normal recurring adjustments necessary for a fair presentation of the Company’s financial position as of March 31, 2026, and results of operations for the interim periods ended March 31, 2026 and March 31, 2025. The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year. These condensed consolidated financial statements should be read in conjunction with the audited financial statements as of and for the years ended December 31, 2025 and 2024, and the notes thereto, included in the Company’s Annual Report on Form 10-K, filed with the SEC on March 4, 2026, or Form 10-K.

Nature of Business and Basis of Presentation

3 Months Ended

Mar. 31, 2026

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Nature of Business and Basis of Presentation

1. Nature of Business and Basis of Presentation

PepGen Inc., hereinafter referred to as PepGen or the Company, is a clinical-stage biotechnology company advancing the next generation of oligonucleotide therapeutics with the goal of transforming the treatment of severe neuromuscular and neurologic diseases. The Company's principal offices are located in Boston, Massachusetts.

Liquidity

Since inception, the Company has not generated any revenue from product sales or other sources and has incurred significant operating losses and negative cash flows from operations. The Company’s primary uses of cash, cash equivalents, and marketable securities to date have been funding research and development activities, business planning, establishing and maintaining the Company’s intellectual property portfolio, hiring personnel, leasing premises and associated capital expenditures, raising capital, and providing general and administrative support for these operations. As of March 31, 2026, the Company had an accumulated deficit of $378.9 million. To date, the Company has funded operations primarily through private placements of convertible preferred stock, the sale of shares of common stock in its initial public offering, or IPO, the sale of shares of common stock under its At-the-Market Equity Offering Sales Agreement, or Sales Agreement, with Stifel, Nicolaus & Company, Incorporated, or Stifel, and through the sale of shares of common stock in follow-on public offerings in February 2024, referred to as the 2024 Offering, and in September 2025, referred to as the 2025 Offering. As of March 31, 2026, the Company had cash, cash equivalents, and marketable securities of $132.3 million.

The Company believes that its cash, cash equivalents, and marketable securities as of March 31, 2026, will be sufficient to fund its currently planned operations for at least the next 12 months from the issuance of these condensed consolidated financial statements.

As the Company continues to pursue its business plan to successfully develop and obtain regulatory approval for its product candidates, it expects to finance its operations through the sale of equity, debt financings or other capital resources, which could include income from collaborations, strategic partnerships or marketing, distribution, licensing or other strategic arrangements with third parties, or from grants. However, there can be no assurance that any additional financing or strategic transactions will be available to the Company on acceptable terms, if at all. If events or circumstances occur such that the Company does not obtain additional funding, it may need to delay, reduce or eliminate its product development or future commercialization efforts, which could have a material adverse effect on the Company’s business, results of operations or financial condition.

Basis of Presentation and Consolidation

The accompanying condensed consolidated financial statements are unaudited and have been prepared in conformity with generally accepted accounting principles in the United States of America, or GAAP. Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification and Accounting Standards Update of the Financial Accounting Standards Board, or FASB.

The condensed consolidated financial statements have been prepared on the same basis as the audited annual financial statements. Certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. These condensed consolidated financial statements, in the opinion of management, reflect all normal recurring adjustments necessary for a fair presentation of the Company’s financial position as of March 31, 2026, and results of operations for the interim periods ended March 31, 2026 and March 31, 2025.

The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year. These condensed consolidated financial statements should be read in conjunction with the audited financial statements as of and for the years ended December 31, 2025 and 2024, and the notes thereto, included in the Company’s Annual Report on Form 10-K, filed with the SEC on March 4, 2026, or Form 10-K.