feat(prometheus): add api_provider label to spend metric (#25693)

* feat(prometheus): add api_provider label to spend metric

Add `api_provider` to `litellm_spend_metric` labels so users can
build Grafana dashboards that break down spend by cloud provider
(e.g. bedrock, anthropic, openai, azure, vertex_ai).

The `api_provider` label already exists in UserAPIKeyLabelValues and
is populated from `standard_logging_payload["custom_llm_provider"]`,
but was not included in the spend metric's label list.

* add api_provider to requests metric + add test

Address review feedback:
- Add api_provider to litellm_requests_metric too (same call-site as
  spend metric, keeps label sets in sync)
- Add test_api_provider_in_spend_and_requests_metrics following the
  existing pattern in test_prometheus_labels.py

litellm/types/integrations/prometheus.py

@@ -396,6 +396,7 @@ class PrometheusMetricLabels:
         UserAPIKeyLabelNames.CLIENT_IP.value,
         UserAPIKeyLabelNames.USER_AGENT.value,
         UserAPIKeyLabelNames.MODEL_ID.value,
+        UserAPIKeyLabelNames.API_PROVIDER.value,
     ]
 
     litellm_spend_metric = [
@@ -410,6 +411,7 @@ class PrometheusMetricLabels:
         UserAPIKeyLabelNames.CLIENT_IP.value,
         UserAPIKeyLabelNames.USER_AGENT.value,
         UserAPIKeyLabelNames.MODEL_ID.value,
+        UserAPIKeyLabelNames.API_PROVIDER.value,
     ]
 
     litellm_input_tokens_metric = [

tests/test_litellm/integrations/test_prometheus_labels.py

@@ -69,6 +69,21 @@ def test_model_id_in_required_metrics():
         print(f"✅ {metric_name} contains model_id label")
 
 
+def test_api_provider_in_spend_and_requests_metrics():
+    """
+    Test that api_provider label is present in spend and requests metrics
+    so users can build spend-by-provider and request-count-by-provider dashboards.
+    """
+    api_provider_label = UserAPIKeyLabelNames.API_PROVIDER.value
+
+    for metric_name in ["litellm_spend_metric", "litellm_requests_metric"]:
+        labels = PrometheusMetricLabels.get_labels(metric_name)
+        assert (
+            api_provider_label in labels
+        ), f"Metric {metric_name} should contain api_provider label"
+        print(f"✅ {metric_name} contains api_provider label")
+
+
 def test_user_email_label_exists():
     """Test that the USER_EMAIL label is properly defined"""
     assert UserAPIKeyLabelNames.USER_EMAIL.value == "user_email"