Pydantic-AI is lovely - I've been working on a forever, fun project to build a coding agent CLI for a year plus now. IMO it does make constructing any given agent very easy, though the lower level APIs are a little painful to use but they seem to be aware of that.
https://github.com/caesarnine/rune-code
Part of the reason I switched to it initially wasn't so much it's niceties versus just being disgusted at how poor the documentation/experience of using LiteLLM was and I thought the folks who make Pydantic would do a better job of the "universal" interface.
I had the opposite experience. I liked the niceties of Pydantic AI, but had trouble with it that I found difficult to deal with. For example, some of the models wouldn't stream, but the OpenAI models did. It took months to resolve, and well before that I switched to LiteLLM and just hand-rolled the agentic logic stuff. LiteLLM's docs were simple and everything worked as expected. The agentic code is simple enough that I'm not sure what the value-add for some of these libraries is besides adding complexity and the opportunity for more bugs. I'm sure for more complex use cases they can be useful, but for most of the applications I've seen, a simple translation layer like LiteLLM or maybe OpenRouter is more than enough.
I'm not sure how long ago you tried streaming with Pydantic AI, but as of right now we (I'm a maintainer) support streaming against the OpenAI, Claude, Bedrock, Gemini, Groq, HuggingFace, and Mistral APIs, as well as all OpenAI Chat Completions-compatible APIs like DeepSeek, Grok, Perplexity, Ollama and vLLM, and cloud gateways like OpenRouter, Together AI, Fireworks AI, Azure AI Foundry, Vercel, Heroku, GitHub and Cerebras.