Pip’s policy is that you should always upgrade to the latest version. I think it’s fine if an older version breaks for newer Python. But I’m less sure that silently installing the wrong package is acceptable. People do use older versions of pip, and loud breakages aren’t the same as silent errors. But we (pip) don’t have a specific policy on this.
I don’t personally have a strong opinion on this, but I do think that if we want people to try out the free-threaded builds, having to debug ABI compatibility issues like this is likely to be rather off-putting for them.