litellm/docs/architecture/router/reference/code-map.md

Code map

Where the router's code lives. Paths are relative to the repo root

flowchart TB
    subgraph py["Python"]
        router["litellm/router.py<br/>Router facade"]
        api["litellm/router_api.py<br/>RouterRegistry, RouterSettings, RouterHealth,<br/>ChangeSet, RoutingContext"]
        corep["litellm/router_core.py<br/>RouterCore, make_core"]
        cfg["litellm/router_config.py<br/>RouterConfig, RouterDynamicConfig"]
        rc["litellm/router_rust_core.py<br/>RustCore step driver"]
        ph["litellm/router_python_host.py<br/>PythonHost"]
        apphost["litellm/router_host.py<br/>RouterHost"]
        plugins["litellm/router_strategy/<br/>Python plugins until ported"]
    end
    subgraph rs["Rust"]
        bridge["litellm-rust/crates/python-bridge/src/router<br/>RouterCoreHandle, RouterCall"]
        core["litellm-rust/crates/router-core<br/>the routing core"]
        gw["gateway<br/>router-core with NativeHost"]
    end
    router --> api & corep & cfg
    corep --> rc
    rc --> ph
    rc --> bridge --> core
    ph -.->|"select bridge"| plugins
    gw --> core

Python

File	Holds
litellm/router.py	Router, the facade. Builds the config, picks the core, delegates every member
litellm/router_api.py	the entry point views and types, see Entry points
litellm/router_core.py	the RouterCore protocol and make_core
litellm/router_config.py	RouterConfig, RouterDynamicConfig, and the only router reads of litellm.* settings
litellm/router_rust_core.py	RustCore, which drives the Rust call loop and answers its steps
litellm/router_python_host.py	PythonHost, the core's host inside a Python process
litellm/router_host.py	RouterHost, what only the application can answer, and litellm/proxy/_router_host.py with the proxy's version
litellm/router_strategy/	Python strategies and sub-routers that run through the select bridge. Each is deleted once its Rust port is the default
litellm/litellm_core_utils/	helpers the router and other modules share, such as wildcard matching, PTU shares and the retry and fallback headers
litellm/types/router.py	Deployment, RoutingGroup, RetryPolicy and the other config types
litellm/proxy/route_llm_request.py	maps a proxy request to a Router endpoint method

Rust

litellm-rust/crates/router-core/src/

File	Holds
lib.rs	Router, RouterBuilder, and the crate overview
config.rs	RouterConfig, RouterDynamicConfig, Op, RoutingStrategy
registry.rs	Registry, Deployment, ChangeSet, name resolution, deployment_id
settings.rs	the frozen Settings view
select.rs	the filter chain and simple-shuffle
call.rs	the call loop, retries and fallbacks
health.rs	cooldowns, allowed fails, usage, and the cache keys
cache.rs	RouterCache and an in-memory implementation
host.rs	Host, Attempt, RouterRequest, RouterEvent, RoutingContext
executor.rs	native routes and NATIVE_RULES
error.rs	ConfigError, Error, AttemptError, FailureKind

litellm-rust/crates/python-bridge/src/router/ exposes the core to Python as RouterCoreHandle and RouterCall, and turns Python's config and dynamic snapshot into the core's types

Tests and checks

Path	What it covers
tests/unit/test_router/core/	the core suite, run against every core builder with a scripted host: selection, retries and cooldowns, fallbacks, registry change sets, endpoints
litellm-rust/crates/router-core unit tests	the Rust modules, with seeded randomness and a test clock
tests/unit/test_router/	router unit tests through the facade, including test_router_entry_points.py
tests/code_coverage_tests/router_surface_check.py	the shrink-only surface allowlist, run in CI
tests/code_coverage_tests/router_litellm_globals_check.py	only litellm/router_config.py reads litellm.* settings
tests/code_coverage_tests/router_code_coverage.py	every router function has a test
litefuzz translation-diff suite	differential fuzzing of one core against another, the parity proof for the swap and for each plugin port