diff --git a/litellm/router.py b/litellm/router.py
index 987c231bffb..306fee83f2d 100644
--- a/litellm/router.py
+++ b/litellm/router.py
@@ -9765,7 +9765,12 @@ class Router:
             }
 
         if model_id is not None:
-            litellm.model_cost.pop(model_id, None)
+            # Deployments key into the same cost map as the built-in catalog, so evict only an
+            # entry this registration owns; a deployment id that names a real model keeps the
+            # old merge rather than stripping what every other deployment of it reads.
+            registered: Final = litellm.model_cost.get(model_id)
+            if registered is not None and registered.get("litellm_provider") is None:
+                litellm.model_cost.pop(model_id, None)
             litellm.register_model(
                 model_cost={model_id: model_info},
                 persist_across_reloads=False,
diff --git a/tests/test_litellm/proxy/management_endpoints/test_model_management_endpoints.py b/tests/test_litellm/proxy/management_endpoints/test_model_management_endpoints.py
index f9dbf6b7e25..17d423bbe04 100644
--- a/tests/test_litellm/proxy/management_endpoints/test_model_management_endpoints.py
+++ b/tests/test_litellm/proxy/management_endpoints/test_model_management_endpoints.py
@@ -3470,6 +3470,45 @@ class TestUpdateDBModelNullClearsAnyKey:
         assert info[field] == _PROTECTED_MODEL_INFO_VALUES[field]
         assert info["max_input_tokens"] == 4096
 
+    def test_echoing_the_read_back_blob_preserves_every_stored_key(self):
+        """The Admin UI edit form submits the whole /model/info row back, and that read reports
+        every key the deployment never stored as an explicit null. Those nulls have to stay
+        no-ops: a write drops None before storing, so a null in the echoed blob always names a
+        key the stored row does not carry.
+        """
+        from litellm.proxy.management_endpoints.model_management_endpoints import (
+            update_db_model,
+        )
+
+        db_model = _build_db_model_with_pinned_model_info()
+        echoed = {
+            "id": "dep-pinned-0",
+            "max_input_tokens": 4096,
+            "mode": "chat",
+            "supports_vision": True,
+            "input_cost_per_token": 0.000001,
+            "team_id": "team-keep-me",
+            "base_model": None,
+            "tier": None,
+            "max_output_tokens": None,
+            "supports_function_calling": None,
+            "cache_read_input_token_cost": None,
+        }
+
+        result = update_db_model(
+            db_model=db_model,
+            updated_patch=updateDeployment.model_validate({"model_info": echoed}),
+        )
+
+        info = json.loads(result["model_info"])
+        assert info["max_input_tokens"] == 4096
+        assert info["mode"] == "chat"
+        assert info["supports_vision"] is True
+        assert info["input_cost_per_token"] == 0.000001
+        assert info["team_id"] == "team-keep-me"
+        for never_stored in ("base_model", "tier", "max_output_tokens", "supports_function_calling"):
+            assert never_stored not in info
+
     def test_null_on_pricing_key_still_clears_both_blobs(self):
         from litellm.proxy.management_endpoints.model_management_endpoints import (
             update_db_model,
diff --git a/tests/test_litellm/test_router_model_cost_isolation.py b/tests/test_litellm/test_router_model_cost_isolation.py
index 5cd67a0f9b3..28cd70425e9 100644
--- a/tests/test_litellm/test_router_model_cost_isolation.py
+++ b/tests/test_litellm/test_router_model_cost_isolation.py
@@ -255,6 +255,35 @@ def test_should_drop_a_price_the_deployment_no_longer_carries():
         _restore_model_cost_entries(original)
 
 
+def test_should_not_strip_a_builtin_entry_when_a_deployment_id_collides_with_it():
+    """Deployments are keyed into the same cost map as the built-in catalog, so a deployment
+    whose id happens to name a real model must not evict that model's entry.
+
+    Stripping it would take the pricing and capability flags every other deployment of that
+    model reads, process-wide, until the next price-map reload.
+    """
+    colliding_id = "gpt-4o"
+    original = {colliding_id: litellm.model_cost.get(colliding_id)}
+    builtin_max_tokens = litellm.model_cost[colliding_id]["max_tokens"]
+
+    try:
+        Router._register_deployment_in_model_cost(
+            model_id=colliding_id,
+            model_info={"id": colliding_id, "db_model": True, "mode": "chat"},
+            model="gpt-4o-mini",
+            custom_llm_provider="openai",
+        )
+
+        entry = litellm.model_cost[colliding_id]
+        assert entry["max_tokens"] == builtin_max_tokens, (
+            "registering a deployment under a catalog model's name wiped that model's context window"
+        )
+        assert entry["litellm_provider"] == "openai"
+        assert entry["supports_vision"] is True
+    finally:
+        _restore_model_cost_entries(original)
+
+
 def test_should_preserve_builtin_pricing_regardless_of_deployment_order():
     """
     The built-in pricing should be preserved no matter which deployment