'PPOConfig' object has no attribute 'api_stack' on Ray 2.20.0

I’m attempting to use the new API stack but am getting an attribute error AttributeError: 'PPOConfig' object has no attribute 'api_stack'. As far as I can tell, I am on Ray 2.20.0 which ought to have the new API stack available.

What am I missing?

The config property api_stack was introduced by [RLlib] AlgorithmConfig cleanup 03: Cleaner names and structuring of API-stack config settings. by sven1977 · Pull Request #44920 · ray-project/ray · GitHub , which is available in ray 2.21.0, but not in the ray 2.20 release.