They're very commonly used in CI. There are dedicated GitHub actions for pre-commit and prek, but most commonly people just invoke something like `prek run --all-files` or `pre-commit run --all-files` in their typical lint CI jobs.

The prek documentation has a list of many large projects (such as CPython and FastAPI, to name a few) who use it; each link is a PR of how they integrated it into CI if you want to see more: https://prek.j178.dev/#who-is-using-prek