litellm/litellm-rust/README.md

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# LiteLLM Rust
This workspace contains the staged Rust implementation for LiteLLM.
`litellm-core` is the LiteLLM SDK in Rust: one entrypoint per top-level call
that makes the LLM call and hands back a typed response, the same shape as
`litellm.messages()` in Python.
```rust
let response = litellm_core::messages::messages(MessagesRequest {
model: "claude-sonnet-4-5",
body,
api_key: Some(key),
..
})
.await?;
```
Python continues to own configuration, retries, routing policy, logging,
callbacks, spend tracking, and customer plugins until each Rust path has parity
coverage and production evidence.
## Crates
| Crate | Role |
|-------|------|
| litellm-core | The SDK. Per-route entrypoints (`messages::messages()`), types, provider transforms (modules under `providers/`), provider resolution, auth, the provider HTTP call, and the router. |
| litellm-ai-gateway | The axum server (behind the `server` feature) and WebSocket hosts. Translates HTTP/WS to core entrypoints; no provider handlers. |
| litellm-python-interop | Domain-neutral PyO3 foundation for GIL handling and typed Python/Serde conversion. |
| litellm-python-bridge | PyO3 cdylib exposing LiteLLM Rust APIs to the Python SDK. Owns API registration, domain wiring, and Python exception mapping. |
Dependency direction is acyclic: `litellm-python-bridge` depends on the domain layers and `litellm-python-interop`; the interop foundation depends on no LiteLLM domain crate.
## Layout
```text
crates/
core/ The SDK: route modules + provider transforms.
src/messages/ mod.rs (entrypoint), types, transformation, prepare, handler, client
src/providers/anthropic/messages/transformation.rs
ai-gateway/ Axum server + WebSocket hosts; calls core entrypoints.
python-interop/ Domain-neutral PyO3 conversion and GIL primitives.
python-bridge/ PyO3 API adapter for Python LiteLLM.
```
The folder shape follows the Python provider tree:
`core/src/providers/<provider>/<route>/transformation.rs`. The bridge exposes one
function per top-level route, mirroring the core entrypoints.
## Checks
Run these before pushing Rust changes. GitHub Actions runs the same checks for
changes under `litellm-rust/`.
```bash
cargo fmt --check
cargo clippy --workspace --all-targets -- -D warnings
cargo test --workspace
```