The situation:
With Docker Engine 29.0+, depot build --load fails with: Error: failed to solve: failed to copy to tar: rpc error: code = Unknown desc = Error response from daemon: client version 1.43 is too old. Minimum supported API version is 1.44, please upgrade your client to a newer version. Docker deprecated API versions <= 1.43, and the depot CLI embedded an older Docker client. Only --load was affected.
What actually fixes it (verified in the thread):
Two options: upgrade the depot CLI to v2.101.6 or later, which works around the Docker API mismatch, or set DOCKER_API_VERSION=1.52 to force a compatible API negotiation. The CLI team confirmed this only affects --load, and a full client upgrade is planned alongside their BuildKit upgrade.