The Great Basedset (also known as Operation Clean Stable and The November 3rd Massacre) refers to a still on-going event that started on 4chan's /qa/ board on 2021-11-03. The board was wiped clean of off-topic threads, leaving 12 threads not counting the board sticky. The following day, 10 additional threads got deleted, leaving only the /hap/ and /nah/ generals remaining. Today only the /hap/ remains, and the board is locked (the opposite of keyed). Trying reply or make thread on /qa/ gives the error message: "Performing site maintenance. Try again in a little while".

In the early stages, it was suggested that the The Great Basedset was carried out in response to a recent raid perpetrated against the /lgbt/ board.[2] It is now known that it runs (((much deeper))) than we could've ever imagined.

Roughly an hour after the event started, an IRC screenshot surfaced which showed 4chan moderator ALTERNATIVE commenting on it.