fix(cost): keep off_peak_pricing scoped to its deployment

register_model inserted the first deployment's off_peak_pricing dict by
reference into the shared backend cost-map entry, and later deployments
sharing that backend merged their schedules into the same object,
corrupting the first deployment's schedule and polluting the built-in
entry. Nested dicts now merge copy-on-write, and off_peak_pricing stays
off the shared backend keys.

litellm/types/utils.py

@@ -3506,17 +3506,22 @@ class CustomPricingLiteLLMParams(MirroredPricingParams):
         return {k: v for k, v in model_info.items() if k not in cls.model_fields}
 
 
-SHARED_BACKEND_MODEL_INFO_FIELDS: Final[frozenset[str]] = frozenset(
-    ModelInfoBase.__required_keys__ | ModelInfoBase.__optional_keys__
-) - frozenset(CustomPricingLiteLLMParams.model_fields)
+DEPLOYMENT_SCOPED_PRICING_FIELDS: Final[frozenset[str]] = frozenset({"off_peak_pricing"})
+
+SHARED_BACKEND_MODEL_INFO_FIELDS: Final[frozenset[str]] = (
+    frozenset(ModelInfoBase.__required_keys__ | ModelInfoBase.__optional_keys__)
+    - frozenset(CustomPricingLiteLLMParams.model_fields)
+    - DEPLOYMENT_SCOPED_PRICING_FIELDS
+)
 
 
 def shared_backend_model_info(model_info: dict[str, Any]) -> dict[str, Any]:
     """Return only the fields safe to register under a shared ``{provider}/{model}``
     key in ``litellm.model_cost``: cost-map schema fields (``ModelInfoBase``) minus
-    per-deployment pricing overrides. Per-deployment metadata (``id``,
-    ``access_via_team_ids``, arbitrary custom keys) never belongs on the shared key;
-    it stays under the deployment's unique model id.
+    per-deployment pricing overrides and deployment-scoped pricing blocks such as
+    ``off_peak_pricing``. Per-deployment metadata (``id``, ``access_via_team_ids``,
+    arbitrary custom keys) never belongs on the shared key; it stays under the
+    deployment's unique model id.
     """
     return {k: v for k, v in model_info.items() if k in SHARED_BACKEND_MODEL_INFO_FIELDS}
 

litellm/utils.py

@@ -2851,10 +2851,9 @@ def _update_dictionary(existing_dict: dict, new_dict: dict) -> dict:
             elif isinstance(v, dict):
                 existing_nested_dict = existing_dict.get(k)
                 if isinstance(existing_nested_dict, dict):
-                    existing_nested_dict.update(v)
-                    existing_dict[k] = existing_nested_dict
+                    existing_dict[k] = {**existing_nested_dict, **v}  # mutable-ok: copy-on-write merge
                 else:
-                    existing_dict[k] = v
+                    existing_dict[k] = dict(v)  # mutable-ok: detached copy, never the caller's dict by reference
             else:
                 existing_dict[k] = v
 

tests/test_litellm/test_register_model_custom_pricing.py

@@ -793,3 +793,101 @@ def test_embedding_direct_sdk_custom_pricing_still_registers_shared_key():
     finally:
         litellm.model_cost.pop(model_key, None)
         _invalidate_model_cost_lowercase_map()
+
+
+def test_update_dictionary_merges_nested_dicts_without_aliasing():
+    """A nested dict must be merged copy-on-write: the pre-existing nested dict
+    object stays untouched, and the caller's incoming nested dict is never
+    inserted by reference into the merged result.
+    """
+    from litellm.utils import _update_dictionary
+
+    existing_nested = {"hours_utc": "01:00-02:00"}
+    existing = {"off_peak_pricing": existing_nested}
+    incoming_nested = {"windows": [{"hours_utc": "16:00-19:00", "weekdays": [2]}]}
+    incoming = {"off_peak_pricing": incoming_nested}
+
+    merged = _update_dictionary(existing, incoming)
+
+    assert merged["off_peak_pricing"] == {
+        "hours_utc": "01:00-02:00",
+        "windows": [{"hours_utc": "16:00-19:00", "weekdays": [2]}],
+    }
+    assert existing_nested == {"hours_utc": "01:00-02:00"}
+    assert merged["off_peak_pricing"] is not incoming_nested
+
+    fresh = _update_dictionary({}, incoming)
+    assert fresh["off_peak_pricing"] == incoming_nested
+    assert fresh["off_peak_pricing"] is not incoming_nested
+
+
+def test_router_deployments_sharing_backend_keep_their_own_off_peak_pricing():
+    """Two deployments of the same backend model with different
+    ``off_peak_pricing`` blocks must each keep their own schedule under their
+    unique model id, and neither block may leak onto the shared backend keys.
+
+    Before the fix, ``register_model`` inserted the first deployment's block by
+    reference into the built-in ``gpt-4o-mini`` entry, and the second
+    deployment's registration merged its keys into that same object, corrupting
+    the first deployment's schedule and polluting the built-in entry.
+    """
+    from litellm import Router
+
+    active_block = {
+        "windows": [{"hours_utc": "16:00-19:00", "weekdays": [2]}],
+        "input_cost_per_token": 5e-07,
+        "output_cost_per_token": 1e-06,
+    }
+    inactive_block = {
+        "hours_utc": "05:00-06:00",
+        "input_cost_per_token": 5e-07,
+        "output_cost_per_token": 1e-06,
+    }
+    shared_keys = ["gpt-4o-mini", "openai/gpt-4o-mini"]
+    deployment_ids = ["offpeak-alias-dep-1", "offpeak-alias-dep-2"]
+    original_entries = _snapshot_model_cost_entries(shared_keys)
+
+    router = Router(
+        model_list=[
+            {
+                "model_name": "offpeak-active-weekday",
+                "litellm_params": {
+                    "model": "openai/gpt-4o-mini",
+                    "api_key": "fake-key-for-registration",
+                },
+                "model_info": {
+                    "id": deployment_ids[0],
+                    "input_cost_per_token": 1e-06,
+                    "output_cost_per_token": 2e-06,
+                    "off_peak_pricing": dict(active_block),
+                },
+            },
+            {
+                "model_name": "offpeak-inactive-hours",
+                "litellm_params": {
+                    "model": "openai/gpt-4o-mini",
+                    "api_key": "fake-key-for-registration",
+                },
+                "model_info": {
+                    "id": deployment_ids[1],
+                    "input_cost_per_token": 1e-06,
+                    "output_cost_per_token": 2e-06,
+                    "off_peak_pricing": dict(inactive_block),
+                },
+            },
+        ]
+    )
+
+    try:
+        registered_first = litellm.model_cost[deployment_ids[0]]["off_peak_pricing"]
+        registered_second = litellm.model_cost[deployment_ids[1]]["off_peak_pricing"]
+        assert registered_first == active_block
+        assert registered_second == inactive_block
+        for shared_key in shared_keys:
+            shared_entry = litellm.model_cost.get(shared_key) or {}
+            assert not shared_entry.get("off_peak_pricing")
+    finally:
+        for deployment_id in deployment_ids:
+            litellm.model_cost.pop(deployment_id, None)
+        _restore_model_cost_entries(original_entries)
+        del router