litellm/litellm-rust/README.md

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.

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-config	Config-loading boundary. Returns resolved deployments and optionally delegates loading to Python.
litellm-gateway-inference	Framework-independent inference services and integrations shared by server and Python hosts.
litellm-gateway-server	Root Axum binary and composition crate. Owns routes, auth, state, startup, and HTTP-only dependencies.
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: config and the gateway runtime depend on core; the gateway server depends on gateway, config, and core; and the Python bridge depends only on reusable domain layers and Python interop.

Layout

crates/
  core/           The SDK: route modules + provider transforms.
    src/messages/   mod.rs (entrypoint), types, transformation, prepare, handler, client
    src/providers/anthropic/messages/transformation.rs
  config/         Config loading and resolved deployments.
  gateway-inference/ Framework-independent inference runtime and integrations.
  gateway-server/    Root Axum binary and route composition host.
  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 the commands under "Checks" in CLAUDE.md before pushing Rust changes. That list is the single source of truth and matches what GitHub Actions runs for changes under litellm-rust/.