Repligen Corporation

Item 3.02 Unregistered Sales of Equity Securities. The Information set forth under Item 8.01 of this Current Report on Form 8-K is incorporated herein by reference.

Item 8.01 Other Events. On October 30, 2026, Repligen Corporation (the “Company”) issued a press release announcing the entry into privately negotiated exchange and/or subscription agreements (the “Exchange/Subscription Agreements”) with certain holders of its outstanding 1.00% Convertible Senior Notes due 2028 (the “2028 Notes”) and certain new investors, pursuant to which the Company will issue $1.0 billion aggregate principal amount of 0.25% Convertible Senior Notes due 2031 (the “New Notes”). Approximately $541.4 million principal amount of the New Notes will be issued in exchange for approximately $456.8 million principal amount of 2028 Notes (the “Exchange Transactions”) and approximately $458.6 million principal amount of the New Notes will be issued for cash (the “Subscription Transactions”, and together with the Exchange Transactions, the “Transactions”). In each case, the New Notes will be issued pursuant to the exemption from registration provided by Section 4(a)(2) of the Securities Act of 1933, as amended (the “Securities Act”). The Company is relying on this exemption from registration based in part on representations made by the investors in the New Notes in the Exchange/Subscription Agreements, including representations that such investors are institutional “accredited investors” within the meaning of Rule 501 of Regulation D under the Securities Act and “qualified institutional buyers” as defined in Rule 144A promulgated under the Securities Act. Following the closing of the Transactions, which is expected to occur on or about November 6, 2026, subject to customary closing conditions, approximately $143.2 million in aggregate principal amount of 2028 Notes will remain outstanding with terms unchanged. The Company estimates that the gross proceeds from the Subscription Transactions will be approximately $458.6 million, excluding fees payable to the placement agent for the Transactions and other offering expenses payable by Repligen. The Company intends to use approximately $120.0 million of the net proceeds from the Subscription Transactions to repurchase shares of its common stock from certain purchasers of the New Notes through a financial intermediary at a price per share of $188.64, which is equal to the last reported sale price of its common stock on October 29, 2026, in order to facilitate the Transactions. The Company intends to use the remainder of the net proceeds for working capital and general corporate purposes, including to fund possible acquisitions of, or investments in, complementary businesses, products, services and technologies. The Company will not receive any cash proceeds from the Exchange Transactions. In connection with the issuance of the New Notes, the Company has been advised that the placement agent for the Transactions intends to purchase approximately $30.0 million of the Company’s common stock from certain participants in the Transactions through a financial intermediary at a discount to the last reported sale price of the common stock on October 29, 2026. Such concurrent repurchases by Repligen and purchases by the placement agent of Repligen’s common stock could increase (or reduce the size of any decrease in) the market price of Repligen’s common stock or the New Notes. When issued: • The New Notes will represent senior unsecured obligations of the Company and will mature on November 1, 2031, unless earlier converted, redeemed or repurchased. • The New Notes will bear interest at a rate of 0.25% per year, starting from November 6, 2026. Interest on the New Notes will be payable semi-annually in arrears on May 1 and November 1 of each year, beginning on May 1, 2027. Additional interest, if any, will accrue on the Notes in the circumstances and at the rates provided in the indenture governing the New Notes. • The New Notes will be convertible at the option of holders in certain circumstances and during certain periods into cash up to the aggregate principal amount of New Notes to be converted, and cash, shares of the Company’s common stock or a combination of cash and the Company’s common stock, at the Company’s election, with respect to the remainder, if any, of the Company's conversion obligation in excess of the aggregate principal amount of New Notes being converted. The initial conversion rate is 4.4176 shares of the Company’s common stock per $1,000 principal amount of New Notes, which is equivalent to an initial conversion price of approximately $226.37 per share, and will be subject to customary anti-dilution adjustments. This represents an approximately 20.0% conversion premium over the last reported sale price of the Company’s common stock on October 29, 2026. • The Company may redeem for cash all or any portion (subject to the partial redemption limitation described below) of the New Notes, at its option, on a redemption date on or after November 6, 2029 and prior to the 21st scheduled trading day immediately preceding the maturity date at a redemption price of 100% of the principal amount of the New Notes to be redeemed, plus accrued and unpaid interest up to, but excluding, the redemption date, if the last reported sale price of its common stock has been at least 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading day period (including the last trading day of such period) ending on, and including, the trading day immediately preceding the date on which the Company provides a notice of redemption; provided that if the Company redeems less than all of the outstanding New Notes, at least $100.0 million aggregate principal amount of New Notes must be outstanding and not subject to redemption as of the relevant redemption notice date. • In addition, subject to certain conditions, on a redemption date prior to the 21st scheduled trading day immediately preceding the maturity date, the Company may redeem for cash all, but not less than all, of the Notes at a redemption price of 100% of the principal amount of the New Notes to be redeemed, plus accrued and unpaid interest to, but excluding the redemption date, if the aggregate principal amount of the Notes that remains outstanding at such time is less than $100 million. If the Company undergoes a “fundamental change” (as defined in the indenture governing the New Notes), subject to certain conditions and except as described in the indenture governing the New Notes, holders may require the Company to repurchase for cash all or part of their New Notes at a purchase price equal to 100% of the principal amount of the New Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date. In addition, if certain “make-whole fundamental changes” (as defined in the indenture governing the New Notes) occur or the Company calls all or a portion of the New Notes for redemption, the Company will, in certain circumstances, increase the conversion rate for any New Notes converted in connection with such make-whole fundamental change or any New Notes called for redemption that are converted during the related redemption period. The New Notes and any of the Company’s common stock issuable upon conversion of the New Notes have not been registered under the Securities Act or under any state securities laws and may not be offered or sold without registration under, or an applicable exemption from, the registration requirements of the Securities Act and any applicable state securities laws. Initially, a maximum of 5,301,100 shares of the Company’s common stock may be issued upon conversion of the New Notes, based on the initial maximum conversion rate for the New Notes, which includes the maximum number of "additional shares" deliverable upon conversion of the New Notes in connection with certain “make-whole fundamental change” transactions or redemptions and is subject to customary anti-dilution adjustments. A copy of the Form of Exchange/Subscription Agreement is filed as Exhibit 99.1 to this Current Report on Form 8-K and is incorporated by reference herein. The foregoing description of the Form of Exchange/Subscription Agreement is qualified in its entirety by reference to such exhibit. A copy of the press release announcing the Transactions is attached hereto as Exhibit 99.2 and is incorporated herein by reference. This Current Report on Form 8-K does not constitute an offer to sell, nor is it a solicitation of an offer to buy, the New Notes or the Company’s common stock, nor shall there be any sale of the New Notes or the Company’s common stock in any state or jurisdiction in which such an offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any state or any jurisdiction.