I don't know the answer to that myself unfortunately. I know the entirety of the runtime itself is OSS and when you do local run/debug of a Function it's the same runtime that Azure uses.

It's not an apples to apples comparison though since OpenWhisk is intended to be self deployed.

I mentioned Functions here just because many folks don't know that most Azure SDKs, runtimes, tooling, etc are OSS by default.