Texter's "Beats me"

IDK

This shorthand reply is often used when someone doesn’t have the answer, and it stands for three words starting with I, D, and K.

"IDK" is a common texting shorthand for "I don’t know," which matches the clue’s phrasing of "Beats me"—a casual way to say the same thing. The clue plays on how texters shorten phrases for speed, so the answer mirrors that informal style. It’s a direct abbreviation swap, with no hidden wordplay or deeper meaning.