diff --git a/litellm/proxy/common_utils/model_deprecation.py b/litellm/proxy/common_utils/model_deprecation.py
index eab58300848..ae807ea14c7 100644
--- a/litellm/proxy/common_utils/model_deprecation.py
+++ b/litellm/proxy/common_utils/model_deprecation.py
@@ -75,23 +75,11 @@ def _mapping_field(deployment: Mapping[str, object], key: str) -> Mapping[str, o
 def _resolve_deployment_deprecation(
     deployment: Mapping[str, object],
 ) -> _ResolvedDeprecation | None:
-    """Resolve a deployment's deprecation date and successor, preferring its explicit overrides"""
+    """Resolve a deployment's deprecation date and successor, preferring its explicit overrides field by field"""
     model_info: Final = _mapping_field(deployment, "model_info")
     raw_model: Final = _mapping_field(deployment, "litellm_params").get("model")
-    explicit_successor: Final = _successor_model(model_info.get("successor_model"))
-
-    override: Final = _parse_deprecation_date(model_info.get("deprecation_date"))
-    if override is not None:
-        provider: Final = model_info.get("litellm_provider")
-        return _ResolvedDeprecation(
-            deprecation_date=override,
-            litellm_model=raw_model if isinstance(raw_model, str) else None,
-            litellm_provider=provider if isinstance(provider, str) else None,
-            successor_model=explicit_successor,
-        )
-
     unprefixed: Final = raw_model.split("/", 1)[1] if isinstance(raw_model, str) and "/" in raw_model else None
-    resolved: Final = next(
+    from_cost_map: Final = next(
         (
             candidate
             for candidate in (
@@ -103,9 +91,20 @@ def _resolve_deployment_deprecation(
         ),
         None,
     )
-    if resolved is None or explicit_successor is None:
-        return resolved
-    return replace(resolved, successor_model=explicit_successor)
+    successor: Final = _successor_model(model_info.get("successor_model")) or (
+        from_cost_map.successor_model if from_cost_map is not None else None
+    )
+
+    override: Final = _parse_deprecation_date(model_info.get("deprecation_date"))
+    if override is not None:
+        provider: Final = model_info.get("litellm_provider")
+        return _ResolvedDeprecation(
+            deprecation_date=override,
+            litellm_model=raw_model if isinstance(raw_model, str) else None,
+            litellm_provider=provider if isinstance(provider, str) else None,
+            successor_model=successor,
+        )
+    return None if from_cost_map is None else replace(from_cost_map, successor_model=successor)
 
 
 def _classify(days_until: int, warn_within_days: int) -> DeprecationStatus:
diff --git a/tests/test_litellm/proxy/common_utils/test_model_deprecation.py b/tests/test_litellm/proxy/common_utils/test_model_deprecation.py
index 3d97450f3f4..68cd9918faf 100644
--- a/tests/test_litellm/proxy/common_utils/test_model_deprecation.py
+++ b/tests/test_litellm/proxy/common_utils/test_model_deprecation.py
@@ -480,3 +480,24 @@ class TestSuccessorModel:
         assert "migrate to `<https://evil.example|new>`" in message
         assert "<https://evil.example|new>" not in message
         assert message.count("migrate to") == 1
+
+    def test_should_take_the_cost_map_successor_when_the_deployment_overrides_only_the_date(self, monkeypatch):
+        monkeypatch.setattr(
+            litellm,
+            "model_cost",
+            {"old-model": {"deprecation_date": "2030-01-01", "successor_model": "new-model"}},
+        )
+        router = _make_router(
+            [
+                {
+                    "model_name": "old",
+                    "litellm_params": {"model": "old-model"},
+                    "model_info": {"id": "1", "deprecation_date": "2026-06-10"},
+                }
+            ]
+        )
+
+        snapshot = collect_model_deprecations(llm_router=router, warn_within_days=30, today=date(2026, 6, 1))
+
+        assert snapshot.imminent[0].deprecation_date == date(2026, 6, 10)
+        assert snapshot.imminent[0].successor_model == "new-model"