From 6c27754455b384a267bae21923a4f50a28d9d6f6 Mon Sep 17 00:00:00 2001
From: mateo-berri <277851410+mateo-berri@users.noreply.github.com>
Date: Fri, 4 Sep 2026 09:26:51 -0700
Subject: [PATCH] fix(anthropic): bill an uncostable partial pass-through
 stream at zero cost instead of dropping its usage

---
 .../anthropic_passthrough_logging_handler.py  | 22 ++++++++++++++-----
 ...t_anthropic_passthrough_logging_handler.py | 13 +++++++++++
 2 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/litellm/proxy/pass_through_endpoints/llm_provider_handlers/anthropic_passthrough_logging_handler.py b/litellm/proxy/pass_through_endpoints/llm_provider_handlers/anthropic_passthrough_logging_handler.py
index dae52bab956..30b75a7b482 100644
--- a/litellm/proxy/pass_through_endpoints/llm_provider_handlers/anthropic_passthrough_logging_handler.py
+++ b/litellm/proxy/pass_through_endpoints/llm_provider_handlers/anthropic_passthrough_logging_handler.py
@@ -240,18 +240,28 @@ class AnthropicPassthroughLoggingHandler:
         usage: Final = cast(Usage | None, getattr(partial_response, "usage", None))
         if partial_response is None or usage is None:
             return
+        litellm_logging_obj.record_partial_usage_for_failure(
+            usage=usage,
+            response_cost=AnthropicPassthroughLoggingHandler._cost_partial_stream_or_zero(
+                partial_response=partial_response, model=model, logging_obj=litellm_logging_obj
+            ),
+        )
+
+    @staticmethod
+    def _cost_partial_stream_or_zero(
+        partial_response: ModelResponse | TextCompletionResponse, model: str, logging_obj: LiteLLMLoggingObj
+    ) -> float:
         try:
-            response_cost: Final = AnthropicPassthroughLoggingHandler._compute_response_cost(
+            return AnthropicPassthroughLoggingHandler._compute_response_cost(
                 litellm_model_response=partial_response,
-                model=AnthropicPassthroughLoggingHandler._resolve_costing_model(model, litellm_logging_obj),
-                logging_obj=litellm_logging_obj,
+                model=AnthropicPassthroughLoggingHandler._resolve_costing_model(model, logging_obj),
+                logging_obj=logging_obj,
             )
-        except Exception as e:  # noqa: BLE001  # an uncostable partial stream must still log as a failure
+        except Exception as e:  # noqa: BLE001  # an uncostable partial stream still bills its tokens, at zero cost
             verbose_proxy_logger.warning(
                 "Anthropic passthrough: could not cost the partial usage of a failed stream (model=%s): %s", model, e
             )
-            return
-        litellm_logging_obj.record_partial_usage_for_failure(usage=usage, response_cost=response_cost)
+            return 0.0
 
     @staticmethod
     def _compute_response_cost(
diff --git a/tests/test_litellm/proxy/pass_through_endpoints/llm_provider_handlers/test_anthropic_passthrough_logging_handler.py b/tests/test_litellm/proxy/pass_through_endpoints/llm_provider_handlers/test_anthropic_passthrough_logging_handler.py
index 480da1d040e..d721be62efe 100644
--- a/tests/test_litellm/proxy/pass_through_endpoints/llm_provider_handlers/test_anthropic_passthrough_logging_handler.py
+++ b/tests/test_litellm/proxy/pass_through_endpoints/llm_provider_handlers/test_anthropic_passthrough_logging_handler.py
@@ -2505,6 +2505,19 @@ class TestRecordPartialUsageForFailure:
         assert usage.prompt_tokens == 52
         assert logging_obj.model_call_details["response_cost"] > 0
 
+    def test_stashes_partial_usage_at_zero_cost_when_model_is_unpriced(self):
+        logging_obj = self._make_logging_obj()
+
+        AnthropicPassthroughLoggingHandler.record_partial_usage_for_failure(
+            litellm_logging_obj=logging_obj,
+            request_body={"model": "claude-unpriced-test-model", "stream": True},
+            all_chunks=self._interrupted_chunks(),
+        )
+
+        usage = logging_obj.model_call_details["combined_usage_object"]
+        assert usage.prompt_tokens == 52
+        assert logging_obj.model_call_details["response_cost"] == 0.0
+
     def test_leaves_logging_obj_untouched_when_nothing_streamed(self):
         logging_obj = self._make_logging_obj()