litellm/litellm-rust

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,
        options: RequestOptions {
            api_key: Some(key.to_string()),
            ..Default::default()
        },
    },
    &LiteLlmRequestContext::default(),
)
.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.

Native request boundary

Native HTTP routes and Responses WebSocket connections accept native(request, *, options, context). The request carries only endpoint payload. NativeRequestOptions carries credentials, typed provider configuration, routing, headers, query parameters, and timeout. NativeRequestContext carries call identity, attribution, and typed capability facts separately from the provider payload.

Python builds the frozen request dataclasses in litellm/rust_bridge/request.py and PyO3 extracts their fields before execution. AWS credentials and metadata policy belong in options.bedrock; Vertex project/location belongs in options.vertex.

This boundary preserves existing Python provider preparation, preflight decisions, fallback, and callbacks

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-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: config depends on core, the gateway depends on config and core, and the Python bridge depends on the 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.
  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 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/.