The Chicago Manual of Style officially released its 18th edition on September 19th, 2024.
You are encouraged to use the new 18th ed. of CMOS formatting; however, your instructor will accept citations done in either the 17th or 18th. Whichever edition you chose to use, make sure that you are consistent in your style across all your source citations.
Please note that resources such as Purdue Owl have not yet updated their information to reflect the changes of the 18th edition. You will need to directly consult the Chicago Manual of Style for formatting guidelines.