diff --git a/litellm/litellm_core_utils/exception_mapping_utils.py b/litellm/litellm_core_utils/exception_mapping_utils.py
index dc245d42862..67a4270e879 100644
--- a/litellm/litellm_core_utils/exception_mapping_utils.py
+++ b/litellm/litellm_core_utils/exception_mapping_utils.py
@@ -68,6 +68,14 @@ class ExceptionCheckers:
         if "service tier capacity exceeded" in _error_str_lower:
             return True
 
+        #######################################
+        # Anthropic returns spend/usage-limit exhaustion typed as an
+        # invalid_request_error (HTTP 400), e.g. "You have reached your specified
+        # API usage limits." It is a usage limit and should map to 429. (#37599)
+        #######################################
+        if "api usage limit" in _error_str_lower:
+            return True
+
         return False
 
     @staticmethod
@@ -536,6 +544,17 @@ def _map_anthropic_exception(
             model=model,
             llm_provider="anthropic",
         )
+    # Anthropic returns usage/spend-limit exhaustion typed as invalid_request_error (400),
+    # but per the exception-mapping docs it should surface as a RateLimitError (429). Check
+    # before the generic 400 branches below, which would otherwise map it to BadRequestError.
+    if ExceptionCheckers.is_error_str_rate_limit(
+        error_str, getattr(original_exception, "status_code", None)
+    ):
+        raise RateLimitError(
+            message=f"AnthropicError - {error_str}",
+            model=model,
+            llm_provider="anthropic",
+        )
     if "Client error '400 Bad Request'" in error_str:
         raise BadRequestError(
             message=f"AnthropicError - {error_str}",
diff --git a/tests/test_litellm/litellm_core_utils/test_exception_mapping_utils.py b/tests/test_litellm/litellm_core_utils/test_exception_mapping_utils.py
index 895044c8ad5..f68c72cc4b7 100644
--- a/tests/test_litellm/litellm_core_utils/test_exception_mapping_utils.py
+++ b/tests/test_litellm/litellm_core_utils/test_exception_mapping_utils.py
@@ -164,6 +164,43 @@ class TestExceptionCheckers:
             is True
         )
 
+    def test_anthropic_usage_limit_is_treated_as_rate_limit(self):
+        """Anthropic reports spend/usage-limit exhaustion as an invalid_request_error
+        (HTTP 400), but it is a usage limit and should map to 429, not 400 (#37599).
+        """
+        error_str = (
+            "litellm.BadRequestError: AnthropicException - "
+            '{"type":"error","error":{"type":"invalid_request_error",'
+            '"message":"You have reached your specified API usage limits. '
+            'You will regain access on 2026-09-01 at 00:00 UTC."}}'
+        )
+        assert ExceptionCheckers.is_error_str_rate_limit(error_str, status_code=400) is True
+
+    def test_anthropic_usage_limit_maps_to_rate_limit_error_end_to_end(self):
+        """Production path: an Anthropic usage-limit error is typed invalid_request_error
+        (HTTP 400). Driving it through exception_type must surface a RateLimitError (429),
+        not a BadRequestError (#37599) — the helper alone is not on the Anthropic mapper.
+        """
+        message = (
+            "AnthropicException - "
+            '{"type":"error","error":{"type":"invalid_request_error",'
+            '"message":"You have reached your specified API usage limits. '
+            'You will regain access on 2026-09-01 at 00:00 UTC."},'
+            '"request_id":"req_011CeDfeyYs7N6neZrLwFxPJ"}'
+        )
+        original_exception = httpx.HTTPStatusError(
+            message=message,
+            request=httpx.Request("POST", "https://api.anthropic.com/v1/messages"),
+            response=httpx.Response(400),
+        )
+
+        with pytest.raises(litellm.RateLimitError):
+            exception_type(
+                model="claude-haiku-4-5-20251001",
+                original_exception=original_exception,
+                custom_llm_provider="anthropic",
+            )
+
     def test_is_azure_content_policy_violation_error_with_policy_violation_text(self):
         """Test detection of Azure content policy violation with explicit policy violation text"""