litellm-router-core implements the router core in Rust: a versioned registry with Python's
deployment ids, selection with native simple-shuffle, the retry, fallback and cooldown loop with
Python's cache keys, and per-attempt executors with a native seam for Messages to Anthropic. The
python bridge exposes it as RouterCoreHandle, whose call loop is step driven so Rust never awaits
Python. RustCore drives that loop for completions, messages, embeddings and responses and serves
everything else from a PythonCore built from the same config. A new router rule in the route
catalog opts in with LITELLM_RUST, and any config the Rust core cannot serve gets PythonCore at
construction
The call loop follows Python's fallback walk (per-target depth, a level raising its own error,
lookup by the current and requested group, "*" after specific chains), stamps retries the way an
exhausted retry loop does, and leaves health writes to the Python attempt, which records them.
RustCore builds its handle from the constructor arguments and the applied changesets and rebuilds
it when either version moves. The core unit suite runs on RustCore too
* refactor(router): move litellm/router.py to litellm/router_python_core.py
A pure rename with no content change, so git and review tools track the router body as a move.
The next commit turns it into PythonCore and adds the Router facade back at litellm/router.py
* refactor(router): extract PythonCore behind RouterCore and pass the router its config
The routing logic moves unchanged from litellm/router.py into PythonCore in
litellm/router_python_core.py. Router becomes a facade that builds a RouterConfig, picks a
RouterCore with make_core and delegates every member to it. The core no longer reads or writes
litellm.* directly: process settings come from RouterDynamicConfig, and inference calls, sleeps,
callback lists and the global cache go through PythonHost. A CI check bans litellm.* in the router
modules, and the proxy's construction sites build the config outside the router
Settings are static: the constructor arguments and changeset values are copied when the router is
built or the change applied, and a write to a setting attribute becomes apply(ChangeSet(assign=...)).
A Router subclass's core class also subclasses the facade, so an override's super(Sub, self) works,
and an instance-level patch of a core method is kept on the facade so nested patches unwind.
tests/unit/test_router/core tests the core in isolation: ScriptedHost serves every host operation
(scripted inference answers, recorded sleeps, settings, callbacks, cache), and make_core runs each
test once per core in CORE_BUILDERS
Code outside the router now reaches it only through the entry points
(registry, settings, health, select, apply, observe, register_plugin, retire)
or the endpoint methods; the outside-member allowlist shrinks from 139 to 45.
litellm/router.py no longer imports litellm.proxy: it asks the installed
RouterHost (litellm/router_host.py) for vertex pass-through credentials,
member auto-router authorization and auto-router prompt compression, and the
proxy installs its host on import. Call sites where a model name can be
missing keep the old answer instead of reaching an entry point with None.
Router gains eight entry points (registry, settings, health, select, apply/aapply,
observe, register_plugin, retire) in litellm/router_api.py. The 123 public members
outside code used become DeprecatedRouterMembers (litellm/router_deprecated.py):
same signatures and results, a DeprecationWarning naming the replacement and a use
counter for callers outside the router. Router internals move to _core_ names;
subclass overrides of old members are still called by the router.
Add rustdoc overviews for a new litellm-router-core crate and for
litellm-model-catalog, a module docstring on litellm/router.py, and a
shrink-only allowlist of the Router members and router_utils modules used
outside the router, checked in CI by router_surface_check.py.
Move the router-free helpers out of litellm/router_utils: batch_utils to
litellm_core_utils, and the auto-router naming contract, tuning baseline
and baseline request next to the auto-router plugin. No behaviour change.
