UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM 10-Q QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended September 30, 2023 Commission file number 1-32737 KOPPERS HOLDINGS INC. (Exact name of registrant as specified in its charter) Pennsylvania 20-1878963 (State of incorporation) (IRS Employer Identification No.) 436 Seventh Avenue Pittsburgh, Pennsylvania 15219 (Address of principal executive offices) (412) 227- ...