> There's only two different LLM APIs in practice (Anthropic and everyone else), and the differences are cosmetic.

There's more than that (even if most other systems also provide a OpenAI compatible API which may or may not expose either all features of the platform or all features of the OpenAI API), and the differences are not cosmetic, but since LiteLLM itself just presents an OpenAI-compatible API, it can't be providing acccess to other vendor features that don't map cleanly to that API, and I don't think its likely to be using the native API for each and being more complete in its OpenAI-compatible implementation of even the features that map naturally than the first-party OpenAI-compatibility APIs.)