Hopefully they backport it to the versions that still have api v3 support. Otherwise the time window for their deprecation of critical functionality and security updates is way too short.
API v3 is still supported in the latest GitLab release (and will also be supported in this month's release, as well as probably the next few since we haven't decided the exact date of deprecation yet), have we communicated this incorrectly somewhere?
We were under the impression that v10 removes it completely. Perhaps this is only in enterprise or maybe we have it wrong? Or maybe it is still included just deprecated but the release notes don't make that clear and no one in my org has checked an actual install or the source.