diff --git a/tests/unit/conftest.py b/tests/unit/conftest.py
index 9028b8461b0..c96e3e2c031 100644
--- a/tests/unit/conftest.py
+++ b/tests/unit/conftest.py
@@ -307,6 +307,30 @@ def isolate_router_model_cost_state() -> Iterator[None]:
     litellm.get_model_info.cache_clear()
 
 
+def _provider_model_sets() -> tuple[set[str], ...]:
+    module_globals: Final = tuple(vars(litellm).items())
+    return tuple(models for name, models in module_globals if name.endswith("_models") and isinstance(models, set))
+
+
+@pytest.fixture(autouse=True)
+def isolate_model_catalog() -> Iterator[None]:
+    model_cost: Final = litellm.model_cost
+    model_cost_entries: Final = dict(model_cost)
+    models_by_provider: Final = litellm.models_by_provider
+    models_by_provider_entries: Final = dict(models_by_provider)
+    provider_model_sets: Final = tuple((models, frozenset(models)) for models in _provider_model_sets())
+    yield
+    model_cost.clear()
+    model_cost.update(model_cost_entries)
+    models_by_provider.clear()
+    models_by_provider.update(models_by_provider_entries)
+    for models, entries in provider_model_sets:
+        models.clear()
+        models.update(entries)
+    litellm_utils_module._invalidate_model_cost_lowercase_map()
+    litellm.get_model_info.cache_clear()
+
+
 @pytest.fixture
 def local_model_cost_map(monkeypatch: pytest.MonkeyPatch) -> Iterator[None]:
     monkeypatch.setenv("LITELLM_LOCAL_MODEL_COST_MAP", "True")
diff --git a/tests/unit/test_conftest_isolation.py b/tests/unit/test_conftest_isolation.py
index 63db0eb5bba..92457119a82 100644
--- a/tests/unit/test_conftest_isolation.py
+++ b/tests/unit/test_conftest_isolation.py
@@ -88,6 +88,26 @@ def test_register_model_ledger_entry_was_rolled_back():
     assert CANARY_MODEL not in litellm_utils_module._runtime_registered_model_cost
 
 
+def test_register_model_catalog_writes_are_scoped_to_this_test():
+    litellm.register_model(
+        {
+            CANARY_MODEL: {"litellm_provider": "openai", "mode": "chat", "input_cost_per_token": 0.001},
+            "collection-isolation-ledger": {"input_cost_per_token": 0.5},
+        }
+    )
+    assert CANARY_MODEL in litellm.model_cost
+    assert CANARY_MODEL in litellm.open_ai_chat_completion_models
+    assert CANARY_MODEL in litellm.models_by_provider["openai"]
+    assert litellm.model_cost["collection-isolation-ledger"]["input_cost_per_token"] == 0.5
+
+
+def test_register_model_catalog_writes_were_rolled_back():
+    assert CANARY_MODEL not in litellm.model_cost
+    assert CANARY_MODEL not in litellm.open_ai_chat_completion_models
+    assert CANARY_MODEL not in litellm.models_by_provider["openai"]
+    assert litellm.model_cost["collection-isolation-ledger"]["input_cost_per_token"] == 0.001
+
+
 def test_live_router_membership_is_scoped_to_this_test():
     _CanaryRouterHolder.router = Router(
         model_list=[
diff --git a/tests/unit/test_utils.py b/tests/unit/test_utils.py
index 0be3ae05e97..40eb5c31fda 100644
--- a/tests/unit/test_utils.py
+++ b/tests/unit/test_utils.py
@@ -2358,7 +2358,6 @@ def test_register_model_with_scientific_notation():
     _invalidate_model_cost_lowercase_map()
 
 
-@pytest.mark.usefixtures("isolated_openai_model_sets")
 @pytest.mark.usefixtures("isolated_openai_model_sets")
 @respx.mock
 def test_register_model_url_fetch_uses_single_attempt(monkeypatch):
@@ -4803,8 +4802,7 @@ async def test_builtin_string_callback_registers_when_subclass_already_active(
     assert any(type(cb) is S3Logger for cb in litellm._async_success_callback)
 
 
-@pytest.mark.usefixtures("isolated_openai_model_sets")
-@pytest.mark.usefixtures("isolated_openai_model_sets")
+@pytest.mark.usefixtures("isolated_openai_model_sets", "local_model_cost_map")
 @pytest.mark.parametrize("rate", (0.0, 0.000123))
 @pytest.mark.parametrize("updated_rate", (None, 0.0, 0.000456))
 def test_reapply_runtime_registrations_replays_register_model_overrides(
@@ -4871,8 +4869,7 @@ def test_reapply_runtime_registrations_replays_register_model_overrides(
         _invalidate_model_cost_lowercase_map()
 
 
-@pytest.mark.usefixtures("isolated_openai_model_sets")
-@pytest.mark.usefixtures("isolated_openai_model_sets")
+@pytest.mark.usefixtures("isolated_openai_model_sets", "local_model_cost_map")
 def test_reapply_runtime_registrations_drops_request_scoped_registrations(monkeypatch):
     """
     Per-request custom pricing describes one call, so it must not be re-asserted