That is true, Bazel itself is still evolving, and there have been breaking changes between versions. Sometimes the required version number is placed in a .bazel

That is true, Bazel itself is still evolving, and there have been breaking changes between versions. Sometimes the required version number is placed in a .bazelversion file, which makes Bazelisk your top-level dependency. I'd expect Tensorflow to have some non-hermetic build actions, but if choosing a specific Bazel version was the only thing that was required to build it, that's awesome!