A quick look at the migration guide (https://docs.pydantic.dev/dev-v2/migration/) and the bump-pydantic script suggests that supporting v2 and v1 at the same time is a bit of a non-starter.

I propose we do the following:

• Pin all the rubin-env <6 to pydantic < 2.
• Change daf_butler et al to first try to import from pydantic.v1 (which is still available in v2) before importing from pydantic. This will let us work with v1 and v2 in the short term.
• Allow v7 to use pydantic but because we learn from our mistakes pin it to <3.
• At some later date after v7 is released we migrate the models over to v2.

Andy Salnikov I've tested this with pydantic v2 and ci_middleware builds fine so it looks like it will be good enough.

I checked daf_butler PR, but I see there are also branches in ctrl_mpexec and ci_middleware without corresponding PRs. Do you want to make PRs for those and have me look at them?

pipe_base branches do not even register in JIRA, maybe we need to clean all outdated branches?

I do clean outdated branches in pipe_base and I'm at a bit of a loss as to why it never shows up. Sorry about the missing PRs – I forgot I hadn't made them yet.

Tim Jenness, do you want to make a PR for ci_middleware or should I mark the ticket as reviewed?

Looks good.