PydanticAI support

[deepc0py]

Any chance you’ll support PydanticAI sometime soon?

[stevenh]

I'm having a look at this for a project, will post once I have something in a decent state.

[tylerslaton]

Hey @stevenh does this mean you're working on a PydanticAI integration with AG-UI? If so we'd love to connect you with some resources on our end.

[NathanTarbert]

Just a quick note, I'm in contact with Pydantic currently.

@stevenh, please let us know how far you've gotten.

[stevenh]

Yes I've made some good progress, the biggest issue so far has been tool support, had to jump through quite a few hoops to allow the pydantic agent to call a tool defined by AG-UI.

The main issue has been having to track state across multiple calls to allow AG-UI process and send the result to a pydantic agent. I'm not sure if this is a bug in copilotkit but currently tool events must be sent on their own and the stream closed to allow the tool to actually be called. This is different to how other events are processed, which happens as soon as they are streamed.

As of 10mins ago I have support for all standard assistant and user messages as well as tools.

[stevenh]

If someone could help reviewing and merging my pending PR's that would help 😃

[stevenh]

More good progress, I have all features now working via our Pydantic AI adapter.

It has full test coverage, so in a pretty good place. I'm going to get an internal review done before getting a repo up for the package and a PR to add the integration example.

[stevenh]

Here's some recording of each feature in action, to wet the appetite 😄

Screen.sharing.-.2025-06-16.12_55_43.PM.mp4

Screen.sharing.-.2025-06-16.12_54_42.PM.mp4

Screen.sharing.-.2025-06-16.12_53_51.PM.mp4

Screen.sharing.-.2025-06-16.12_52_44.PM.mp4

Screen.sharing.-.2025-06-16.12_50_51.PM.mp4

Screen.sharing.-.2025-06-16.11_56_30.AM.mp4

[tylerslaton]

This is incredible @stevenh! We're going to give this a review soon but bravo.

[tylerslaton]

Would there be any chance that you could put up the PR for the actual Pydantic AI support as well? Mainly just to sanity check the implementation.

[stevenh]

Absolutely, doing some docs and will get it up ASAP. Would love an expert review ☺️

[NathanTarbert]

Amazing work @stevenh!

[stevenh]

Quick update, passed internal review, so extracting now to get more 👀 on.

I picked up the MCP metadata feature last night, so depending on how long that takes to get over the line, it might be worth waiting for pydantic/pydantic-ai#2000 as that will allow for a simpler flow.

[DouweM]

@stevenh Douwe from Pydantic AI here, we're very eager to see the AG-UI integration you built! Keep filing issues and PRs -- I'll review that one shortly.

[stevenh]

Quick update for folks, there's been some conversations happening between teams, which has resulted in a slight change in direction. The plan is now to provide an out of the box AG-UI as part of PydanticAI.

This is great news as it means it can be tighter integration meaning much easier to setup.

Thanks to the support from @DouweM I'm looking to adjust what I had to provide this more integrated solution. I managed to get the base of that done today, but we'd like to eliminate the state management if possible which will require a little more effort.

Depending on any issues that might arise, I should have something for people to look at in the next few days.