Code map

Since v1.110.0

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

Python

File	Holds
litellm/router.py	Router, the facade. It builds the config, chooses the core and delegates every member
litellm/router_api.py	the entry point views and types, see Entry points, plus ROUTER_INIT_ARGS and apply_changes
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_deprecated.py	DeprecatedRouterMembers, the old member names with a DeprecationWarning
litellm/router_python_host.py	PythonHost, the host inside a Python process: endpoint functions, sleep, dynamic config, callbacks, caches
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/	the stateful strategies, lar1, the sub-routers, the budget limiter and tag routing. The core reaches them through the select and pre-route steps
litellm/router_utils/	helpers the host uses, such as the cooldown cache, the health state cache, pre-call checks and the response headers
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

litellm/router_rust/

Everything the core needs on the Python side.

Path	Holds
core.py	RustCore, the step driver for async and sync calls
steps/	answers to the steps that need live Python objects: selection.py (strategies), prerouting.py (sub-routers, session binding, custom strategies), precall.py (pre-call facts), plugins.py (Router(plugins=[...])), callbacks.py (CustomLogger filters), access.py (caller access facts)
invoke/	one attempt: endpoints.py (the endpoint wrappers), shaping.py (request and response shaping), streaming.py (stream wrappers that report the outcome when a stream ends), slots.py (max_parallel_requests), walk.py (retry and fallback metadata), prompt_management.py, websocket.py
surface/	the Python Router API over the core's state: registry.py, model_list.py, indexes.py, members.py, model_info.py, settings.py, health.py, health_routing.py, retries.py, fallbacks.py, alerting.py, replay.py

litellm/router_attempt.py builds the keyword arguments of one attempt for the deployment the core picked. It does not pick, retry or record anything.

Rust

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

File	Holds
lib.rs	Router, RouterBuilder, and the crate overview
config.rs	RouterConfig, RouterDynamicConfig, Op, RoutingStrategy, retry and allowed fails policies
registry.rs	Registry, Deployment, ChangeSet, deployment_id
build.rs	building deployments from config with the host's secrets, validate, provider and added steps
resolve.rs	name resolution, a port of _common_checks_available_deployment
select.rs	the filter chain and simple-shuffle
access.rs, ptu.rs, health_routing.rs, precall.rs	the access group and window, PTU share, health check and pre-call filters
prerouting.rs, routing_plugins.rs, routing_groups.rs	pre-routing, routing plugin candidates and routing group members
strategy.rs, weights.rs	which strategy a pick uses, and per-request weights
call.rs, call/stream.rs	the call loop with retries, fallbacks and weighted failover, and stream recovery
retry.rs, fallback.rs, mock.rs	retry rules, the fallback lists, and mock_testing_* failures
health.rs	cooldowns, allowed fails, usage, and the cache keys
cache.rs	RouterCache and an in-memory implementation for tests
settings.rs	the frozen Settings view
host.rs	Host, Attempt, RouterRequest, RouterEvent, RoutingContext
lookup.rs, host_index.rs	the indexes and listings the Python surface reads
model_info.rs, group_info.rs	model info and model group info merges
error.rs	ConfigError, Error, AttemptError, FailureKind

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

Tests and checks

Path	What it covers
tests/unit/test_router/core/	the core suite, run against the core 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	checks that only litellm/router_config.py reads litellm.* settings
tests/code_coverage_tests/router_code_coverage.py	checks that every router function has a test
litefuzz translation-diff suite	differential fuzzing of routing behavior, run on every change to the core