UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of report (Date of earliest event reported): July 24, 2026 SELLAS Life Sciences Group, Inc. (Exact name of registrant as specified in its charter) (State or other jurisdiction of incorporation or organization) (Commission File Number) Delaware 001-33958 20-8099512 (I.R.S. Employer Identification No.) 7 Times Square, Suite 2503 New York, N ...