Material Agreement, Financial Obligation (Form 8-K)

On October 10, 2025 (the "Closing Date"), Karyopharm Therapeutics Inc. (the "Company") closed a series of transactions with its term loan lenders, holders of its then-outstanding convertible notes and other investors, which were previously announced by the Company on October 8, 2025 (collectively, the "Financing Transactions").

On the Closing Date, the Company entered into (i) an indenture with respect to the Company's 9.00% convertible senior notes due 2028, dated October 10, 2025, between the Company, the guarantors party thereto and Wilmington Savings Fund Society, FSB ("WSFS"), as trustee and collateral agent, (ii) an indenture with respect to the Company's 9.00% convertible senior notes due 2029, dated October 10, 2025, between the Company, the guarantors party thereto and WSFS, as trustee and collateral agent and (iii) registration rights agreements, dated October 10, 2025, with each of the term loan lenders, in each case on the terms described in the Current Report on Form 8-Kfiled by the Company on October 8, 2025.

The representations, warranties and covenants contained in the various agreements and other documents included as exhibits herewith were made solely for the benefit of the parties thereto and may be subject to limitations agreed upon by the contracting parties. Accordingly, these agreements and documents are only to provide investors with information regarding the terms thereof and not to provide investors with any other factual information regarding the Company or its business, and such agreements and documents should be read in conjunction with the disclosures in the Company's periodic reports and other filings with the Securities and Exchange Commission.

On the Closing Date and as disclosed in the Current Report on Form 8-Kfiled by the Company on October 8, 2025, the Company borrowed $12.5 million under its credit and guaranty agreement, as amended, by the First Amendment and Waiver to Credit and Guaranty Agreement dated as of October 7, 2025.

On the Closing Date and as disclosed in the Current Report on Form 8-Kfiled by the Company on October 8, 2025, the Company issued $15.0 million aggregate principal amount of 9.00% senior secured convertible notes due 2028 and $103.5 million aggregate principal amount of 9.00% senior secured convertible notes due 2029.

As of October 14, 2025, the Company has 15,926,939 shares of common stock outstanding (assuming no exercise of any outstanding pre-fundedwarrants or warrants or conversions of any outstanding convertible notes issued in the Financing Transactions).