fix(anthropic): derive the count-tokens URL from the deployment api_base

litellm/llms/anthropic/count_tokens/handler.py

@@ -41,7 +41,7 @@ class AnthropicCountTokensHandler(AnthropicCountTokensConfig):
             model: The model identifier (e.g., "claude-3-5-sonnet-20241022")
             messages: The messages to count tokens for
             api_key: The Anthropic API key
-            api_base: Optional custom API base URL
+            api_base: Optional deployment api_base the count-tokens path is appended to
             timeout: Optional timeout for the request (defaults to litellm.request_timeout)
 
         Returns:
@@ -67,7 +67,7 @@ class AnthropicCountTokensHandler(AnthropicCountTokensConfig):
             verbose_logger.debug("Transformed request: %s", request_body)
 
             # Get endpoint URL
-            endpoint_url: Final = api_base or self.get_anthropic_count_tokens_endpoint()
+            endpoint_url: Final = self.get_anthropic_count_tokens_endpoint(api_base)
 
             verbose_logger.debug("Making request to: %s", endpoint_url)
 

litellm/llms/anthropic/count_tokens/transformation.py

@@ -7,6 +7,7 @@ This module handles the transformation of requests to Anthropic's CountTokens AP
 from typing import Any, Final
 
 from litellm.constants import ANTHROPIC_TOKEN_COUNTING_BETA_VERSION
+from litellm.llms.anthropic.wif import anthropic_base_without_chat_suffix
 
 
 class AnthropicCountTokensConfig:
@@ -19,14 +20,21 @@ class AnthropicCountTokensConfig:
     - Response: {"input_tokens": <number>}
     """
 
-    def get_anthropic_count_tokens_endpoint(self) -> str:
+    def get_anthropic_count_tokens_endpoint(self, api_base: str | None = None) -> str:
         """
         Get the Anthropic CountTokens API endpoint.
 
+        Args:
+            api_base: The deployment's api_base, which names the chat surface (a host, or a
+                base already carrying ``/v1`` or ``/v1/messages``); the count-tokens path is
+                appended to it, so it is never the full count-tokens URL
+
         Returns:
             The endpoint URL for the CountTokens API
         """
-        return "https://api.anthropic.com/v1/messages/count_tokens"
+        if api_base is None:
+            return "https://api.anthropic.com/v1/messages/count_tokens"
+        return anthropic_base_without_chat_suffix(api_base) + "/v1/messages/count_tokens"
 
     def transform_request_to_count_tokens(
         self,

tests/test_litellm/llms/anthropic/test_anthropic_count_tokens_transformation.py

@@ -1,3 +1,9 @@
+import httpx
+import pytest
+import respx
+
+import litellm
+from litellm.llms.anthropic.count_tokens.handler import AnthropicCountTokensHandler
 from litellm.llms.anthropic.count_tokens.transformation import (
     AnthropicCountTokensConfig,
 )
@@ -87,3 +93,47 @@ def test_transform_no_system_no_tools():
 
     assert "system" not in result
     assert "tools" not in result
+
+
+@pytest.mark.parametrize(
+    ("api_base", "expected"),
+    [
+        (None, "https://api.anthropic.com/v1/messages/count_tokens"),
+        ("https://gateway.example", "https://gateway.example/v1/messages/count_tokens"),
+        ("https://gateway.example/", "https://gateway.example/v1/messages/count_tokens"),
+        ("https://gateway.example/v1", "https://gateway.example/v1/messages/count_tokens"),
+        ("https://gateway.example/anthropic/v1/messages", "https://gateway.example/anthropic/v1/messages/count_tokens"),
+    ],
+)
+def test_endpoint_appends_count_tokens_path_to_deployment_api_base(api_base, expected):
+    assert AnthropicCountTokensConfig().get_anthropic_count_tokens_endpoint(api_base) == expected
+
+
+@pytest.fixture
+def httpx_transport_clients(monkeypatch):
+    monkeypatch.setattr(litellm, "disable_aiohttp_transport", True)
+    client_cache = getattr(litellm, "in_memory_llm_clients_cache", None)
+    if client_cache is not None:
+        client_cache.flush_cache()
+    yield
+    if client_cache is not None:
+        client_cache.flush_cache()
+
+
+@pytest.mark.asyncio
+async def test_handler_posts_to_count_tokens_path_under_deployment_api_base(httpx_transport_clients):
+    """A deployment api_base names the chat host, so a handler that posts to it verbatim lands on
+    the host root, gets a 404, and the official count silently degrades to the local tokenizer."""
+    with respx.mock:
+        route = respx.post("https://gateway.example/v1/messages/count_tokens").mock(
+            return_value=httpx.Response(200, json={"input_tokens": 7})
+        )
+        result = await AnthropicCountTokensHandler().handle_count_tokens_request(
+            model="claude-sonnet-4-5",
+            messages=[{"role": "user", "content": "hi"}],
+            api_key="sk-ant-api03-test-key",
+            api_base="https://gateway.example",
+        )
+
+    assert route.called
+    assert result == {"input_tokens": 7}