diff --git a/litellm/litellm_core_utils/logging_callback_manager.py b/litellm/litellm_core_utils/logging_callback_manager.py
index 56c6436eae6..bc5dfdc9a10 100644
--- a/litellm/litellm_core_utils/logging_callback_manager.py
+++ b/litellm/litellm_core_utils/logging_callback_manager.py
@@ -2,6 +2,7 @@ import threading
 from collections.abc import Callable, Iterable, Iterator, Mapping
 from types import MethodType
 from typing import TYPE_CHECKING, Final
+from weakref import WeakSet
 
 import litellm
 from litellm._logging import verbose_logger
@@ -19,6 +20,14 @@ else:
 _generic_api_logger_cache: Final[dict[str, GenericAPILogger]] = {}
 _callback_lists_lock: Final = threading.RLock()
 
+# CustomLoggers registered with `dedupe_by_identity=True` (router strategy
+# selectors) keep identity-based membership when another code path re-adds them
+# to a different list. `function_setup` copies `litellm.callbacks` into the
+# success/failure event lists, and the class-key dedup there would otherwise
+# drop a second live instance again, leaving the newest Router's cache empty
+# (issue #44575). Weakly held so a discarded logger does not leak.
+_identity_deduped_loggers: Final[WeakSet[CustomLogger]] = WeakSet()
+
 
 def _instance_attributes(target: object) -> Mapping[str, object]:
     return vars(target)
@@ -45,16 +54,35 @@ class LoggingCallbackManager:
         except Exception:
             return False
 
-    def add_litellm_input_callback(self, callback: CustomLogger | str | Callable[..., object]):
+    def add_litellm_input_callback(
+        self,
+        callback: CustomLogger | str | Callable[..., object],
+        dedupe_by_identity: bool = False,
+    ):
         """
         Add a input callback to litellm.input_callback.
         Auto-routes async callbacks to litellm._async_input_callback.
+
+        Args:
+            callback: the callback to add.
+            dedupe_by_identity: if True, CustomLogger instances are deduped by
+                object identity instead of the class-level key. Required for
+                per-instance stateful loggers (router strategy selectors) where
+                two live instances of the same class must coexist.
         """
         with _callback_lists_lock:
             if not isinstance(callback, str) and self._is_async_callable(callback):
-                self._safe_add_callback_to_list(callback=callback, parent_list=litellm._async_input_callback)
+                self._safe_add_callback_to_list(
+                    callback=callback,
+                    parent_list=litellm._async_input_callback,
+                    dedupe_by_identity=dedupe_by_identity,
+                )
             else:
-                self._safe_add_callback_to_list(callback=callback, parent_list=litellm.input_callback)
+                self._safe_add_callback_to_list(
+                    callback=callback,
+                    parent_list=litellm.input_callback,
+                    dedupe_by_identity=dedupe_by_identity,
+                )
 
     def add_litellm_service_callback(self, callback: CustomLogger | str | Callable[..., object]):
         """
@@ -63,16 +91,28 @@ class LoggingCallbackManager:
         with _callback_lists_lock:
             self._safe_add_callback_to_list(callback=callback, parent_list=litellm.service_callback)
 
-    def add_litellm_callback(self, callback: CustomLogger | str | Callable[..., object]):
+    def add_litellm_callback(
+        self,
+        callback: CustomLogger | str | Callable[..., object],
+        dedupe_by_identity: bool = False,
+    ):
         """
         Add a callback to litellm.callbacks
 
         Ensures no duplicates are added.
+
+        Args:
+            callback: the callback to add.
+            dedupe_by_identity: if True, CustomLogger instances are deduped by
+                object identity instead of the class-level key. Required for
+                per-instance stateful loggers (router strategy selectors) where
+                two live instances of the same class must coexist.
         """
         with _callback_lists_lock:
             self._safe_add_callback_to_list(
                 callback=callback,
                 parent_list=litellm.callbacks,
+                dedupe_by_identity=dedupe_by_identity,
             )
 
     def add_litellm_success_callback(self, callback: CustomLogger | str | Callable[..., object]):
@@ -268,11 +308,17 @@ class LoggingCallbackManager:
         self,
         callback: CustomLogger | Callable[..., object] | str,
         parent_list: list[CustomLogger | Callable[..., object] | str],
+        dedupe_by_identity: bool = False,
     ):
         """
         Safe add a callback to a list, if the callback is already in the list, do not add it again.
 
         Ensures no duplicates are added for `str`, `Callable`, and `CustomLogger` callbacks.
+
+        Args:
+            dedupe_by_identity: forwarded to `_add_custom_logger_to_list` — dedupe
+                ``CustomLogger`` instances by object identity instead of the
+                class-level key.
         """
         # Check max callbacks limit first
         if not self._check_callback_list_size(parent_list):
@@ -289,6 +335,7 @@ class LoggingCallbackManager:
             self._add_custom_logger_to_list(
                 custom_logger=callback,
                 parent_list=parent_list,
+                dedupe_by_identity=dedupe_by_identity,
             )
 
         elif callable(callback):
@@ -314,10 +361,36 @@ class LoggingCallbackManager:
         self,
         custom_logger: CustomLogger,
         parent_list: list[CustomLogger | Callable[..., object] | str],
+        dedupe_by_identity: bool = False,
     ):
         """
         Add a custom logger to a list, if another instance of the same custom logger exists in the list, do not add it again.
+
+        Args:
+            dedupe_by_identity: if True, dedupe by object identity instead of
+                the class-level key. Required for per-instance stateful loggers
+                (router strategy selectors) where two live instances of the same
+                class must coexist.
         """
+        # Per-instance loggers are deduped by identity: their class-level key
+        # does not distinguish two live instances, and silently dropping the
+        # second one leaves the newest Router with an unregistered callback
+        # (see issue #44575). Once a logger is registered by identity, every
+        # later list it is promoted into (e.g. `function_setup` copying
+        # `litellm.callbacks` into the success/failure event lists) must keep
+        # that mode, or the second instance is dropped again there.
+        if dedupe_by_identity or any(existing is custom_logger for existing in _identity_deduped_loggers):
+            _identity_deduped_loggers.add(custom_logger)
+            if not any(existing is custom_logger for existing in parent_list):
+                parent_list.append(custom_logger)
+            else:
+                verbose_logger.debug(
+                    "Custom logger instance %s already exists in %s, not adding again..",
+                    custom_logger,
+                    parent_list,
+                )
+            return
+
         # Check if an instance of the same class already exists in the list
         custom_logger_key: Final = self._get_custom_logger_key(custom_logger)
         custom_logger_type_name: Final = type(custom_logger).__name__
diff --git a/litellm/router_python_core.py b/litellm/router_python_core.py
index 30b05456987..68bcb586074 100644
--- a/litellm/router_python_core.py
+++ b/litellm/router_python_core.py
@@ -2275,13 +2275,20 @@ class PythonCore(DeprecatedRouterMembers):
         return selector
 
     def _register_router_selector(self, selector: CustomLogger) -> None:
+        # Strategy selectors are per-instance stateful callbacks (each holds
+        # its own Router cache), so they must be deduped by identity: the
+        # class-level key treats a second Router's selector as a duplicate of
+        # the first one and silently drops it, leaving the new Router's
+        # latency/usage cache permanently empty (issue #44575). Least-busy
+        # never hit this by luck — its instances differ in a scalar attribute,
+        # so their keys never collided.
         if isinstance(selector, LeastBusyLoggingHandler):
             if isinstance(self._host.callback_list("input_callback"), list):
-                self._host.callbacks.add_litellm_input_callback(selector)
+                self._host.callbacks.add_litellm_input_callback(selector, dedupe_by_identity=True)
             else:
                 self._host.set_callback_list("input_callback", [selector])
         if isinstance(self._host.callback_list("callbacks"), list):
-            self._host.callbacks.add_litellm_callback(selector)
+            self._host.callbacks.add_litellm_callback(selector, dedupe_by_identity=True)
 
     def _callback_selectors(self) -> tuple[RouterStrategySelector, ...]:
         return tuple(
diff --git a/tests/unit/litellm_core_utils/test_logging_callback_manager.py b/tests/unit/litellm_core_utils/test_logging_callback_manager.py
index 25a52137d65..5d26072f1ab 100644
--- a/tests/unit/litellm_core_utils/test_logging_callback_manager.py
+++ b/tests/unit/litellm_core_utils/test_logging_callback_manager.py
@@ -344,3 +344,44 @@ def test_duplicate_multiple_loggers_test():
 
     assert langfuse_count == 1, "Should have exactly one LangfusePromptManagement instance"
     assert otel_count == 1, "Should have exactly one OpenTelemetry instance"
+
+
+def test_add_custom_logger_default_mode_dedupes_same_class_instances():
+    """
+    Default mode keeps one instance per CustomLogger class: the class-level
+    key treats a second instance of the same class as a duplicate.
+    """
+    manager = LoggingCallbackManager()
+
+    class TestLogger(CustomLogger):
+        pass
+
+    first, second = TestLogger(), TestLogger()
+
+    manager.add_litellm_callback(first)
+    manager.add_litellm_callback(second)
+
+    assert sum(1 for c in litellm.callbacks if c is first) == 1
+    assert all(c is not second for c in litellm.callbacks)
+
+
+def test_add_custom_logger_dedupe_by_identity_allows_two_instances():
+    """
+    `dedupe_by_identity=True` is required for per-instance stateful loggers
+    (router strategy selectors): two live instances of the same class must
+    coexist, while re-adding the same instance stays a no-op.
+    """
+    manager = LoggingCallbackManager()
+
+    class TestLogger(CustomLogger):
+        pass
+
+    first, second = TestLogger(), TestLogger()
+
+    manager.add_litellm_callback(first, dedupe_by_identity=True)
+    manager.add_litellm_callback(second, dedupe_by_identity=True)
+    assert sum(1 for c in litellm.callbacks if c is first) == 1
+    assert sum(1 for c in litellm.callbacks if c is second) == 1
+
+    manager.add_litellm_callback(first, dedupe_by_identity=True)
+    assert sum(1 for c in litellm.callbacks if c is first) == 1
diff --git a/tests/unit/router_strategy/test_router_routing_groups.py b/tests/unit/router_strategy/test_router_routing_groups.py
index 5eeb46c3518..deb604f3f1f 100644
--- a/tests/unit/router_strategy/test_router_routing_groups.py
+++ b/tests/unit/router_strategy/test_router_routing_groups.py
@@ -2255,3 +2255,84 @@ async def test_update_settings_changed_routing_strategy_args_flushes_replaced_se
                 await t
             except asyncio.CancelledError:
                 pass
+
+
+def _reset_global_callback_lists(monkeypatch) -> None:
+    """Every global callback list, so a Router built here does not see selectors
+    promoted by an earlier test (monkeypatch would not restore those)."""
+    for name in (
+        "callbacks",
+        "input_callback",
+        "success_callback",
+        "failure_callback",
+        "_async_success_callback",
+        "_async_failure_callback",
+    ):
+        monkeypatch.setattr(litellm, name, [])
+
+
+def test_two_routers_same_latency_strategy_both_register_selectors(monkeypatch):
+    """
+    Two Routers with `latency-based-routing` in one process must both see their
+    default selector registered: the latency handler's class-level dedup key is
+    identical for every instance (no scalar instance attributes), so key-based
+    dedup silently dropped the second Router's selector and its latency cache
+    never got populated (issue #44575).
+    """
+    _reset_global_callback_lists(monkeypatch)
+
+    first = _build_router(routing_strategy="latency-based-routing")
+    second = _build_router(routing_strategy="latency-based-routing")
+
+    first_selector = first.lowestlatency_logger
+    second_selector = second.lowestlatency_logger
+    assert first_selector is not None and second_selector is not None
+    assert first_selector is not second_selector
+    assert any(c is first_selector for c in litellm.callbacks)
+    assert any(c is second_selector for c in litellm.callbacks), (
+        "second Router's latency selector was dropped by the callback dedup"
+    )
+
+
+def test_second_latency_router_receives_events_through_the_normal_logging_path(monkeypatch):
+    """
+    Registering both selectors in `litellm.callbacks` is not enough: the normal
+    request path (`function_setup`) copies those callbacks into the success and
+    failure event lists, and that copy used to dedupe by class key and drop the
+    second Router's selector again. Drive `function_setup` and the success
+    dispatch here instead of calling the selectors directly (issue #44575).
+    """
+    _reset_global_callback_lists(monkeypatch)
+
+    first = _build_router(routing_strategy="latency-based-routing")
+    second = _build_router(routing_strategy="latency-based-routing")
+    second_selector = second.lowestlatency_logger
+
+    start_time = datetime.datetime(2026, 1, 1)
+    logging_obj, _ = function_setup(
+        "completion",
+        Rules(),
+        start_time,
+        litellm_call_id=str(uuid.uuid4()),
+        messages=[{"role": "user", "content": "hi"}],
+        model="filtered-model",
+        metadata={"model_group": "filtered-model"},
+        model_info={"id": "deploy-1"},
+    )
+
+    # The promotion into the event lists is where the second instance used to be
+    # dropped, which the `litellm.callbacks` assertion above cannot see.
+    assert any(cb is second_selector for cb in litellm.success_callback), (
+        "function_setup dropped the second Router's selector from the success event list"
+    )
+    assert any(cb is second_selector for cb in litellm.failure_callback)
+    assert any(cb is second_selector for cb in litellm._async_success_callback)
+
+    logging_obj.success_handler(
+        result=None,
+        start_time=start_time,
+        end_time=start_time + datetime.timedelta(seconds=0.5),
+    )
+
+    assert first.cache.get_cache("filtered-model_map") is not None
+    assert second.cache.get_cache("filtered-model_map") is not None