Even though of us who have been hacking away for awhile have TIL days. This one is courtesy of @SenseTalkDoug
//Need to extract text within parentheses from a longer text string
set myText to "ABC Activity: Test #1 (ABC-2025-123456ABC.00) blah"
set inParentheses to <leftParenthesis , {theGoodStuff:some characters}, rightParenthesis>
put (the match of inParentheses in myText).theGoodStuff
Reference: Pattern Matching Functions | EPF Docs