300 developers' work being crammed together into a weekly release without having their contributions pass CI first sounds absolutely hellish for whatever poor bastard has to track down who broke the build.

There's tooling like bors that will rollup commits together and run CI on them before merging to master. If it fails then the commits will be retried individually.

I suppose so, but that cuts down on the number of CI runs when merging to master because the vast majority of commits being merged to master don't fail the build.

In a typical bors workflow, that holds, because you do a CI run before attempting to merge, so commits don't break the build except in the rare case that two commits that are individually okay combine in a way that breaks.

If you get rid of the individual run before merging, your combined runs will hardly ever pass, so it won't cut down on the number of runs.

Yes, I suppose I could be taking the anecdote too literally. It's much more likely they are only running all test on push to main / against pull requests / on code review.