Management Change/Compensation (Form 8-K)

On July 13, 2026, the Board of Directors (the "Board") of Karyopharm Therapeutics Inc. (the "Company"), upon recommendation of its Compensation Committee, implemented a retention program for certain employees of the Company, including each of the Company's named executive officers and the Chief Financial Officer (the "2026 Leadership Cash Retention Program"). The purpose of the 2026 Leadership Cash Retention Program is to incentivize retention of key employees during a period in which the Company is expecting several meaningful catalysts requiring the continued experience and expertise of the designated employees. The 2026 Leadership Cash Retention Program replaces previously guaranteed amounts under the Company's Annual Bonus Plan for 2026. Under the 2026 Leadership Cash Retention Program, the Company's named executive officers and the Chief Financial Officer will receive lump sum cash retention awards in the following amounts: Richard Paulson, President and Chief Executive Officer, $1,725,000; Stuart Poulton, Executive Vice President, Chief Development Officer, $640,000; Dr. Reshma Rangwala, Executive Vice President, Chief Medical Officer and Head of Research, $725,000; and Lori Macomber, Executive Vice President, Chief Financial Officer and Treasurer, $625,000. Awards under the 2026 Leadership Cash Retention Program may be subject to repayment if the recipient's employment is terminated for any reason other than by the Company without cause, by the participant for good reason or due to the participant's death or permanent disability prior to the earlier of (i) 12 months from the payment date and (ii) 30 days following a qualifying corporate event. Amounts paid under the 2026 Leadership Cash Retention Program will reduce any amounts payable under previously agreed upon severance arrangements.

2