The PEP page is really good at explaining the status of the proposal, a summary of the discussion to date, and then links to the actual detailed discussion (in Discourse) about it:
I see this was accepted (I think?); is the implementation available in a released python version? I don't see an "as of" version on the pep page, nor do lite google searches reveal any official python docs of the feature.
It's not a python the language feature, it's for packaging. So no language version is relevant. It's just there for any tool that wants to use it. uv, an IDE, or anything else that manages virtual environments would be the ones who implement it independent of python versions.
This is a specification for Python packaging, which is tooling separate from Python releases (for better or worse, IMHO worse but the BDFL disagrees). There's a box below the Table of Contents of the PEP that points here:
https://peps.python.org/pep-0723/