[Bugfix] Add Responses cache_write_tokens for API compat and CC parity (#57222)

Signed-off-by: Yifan Zong <yzong@redhat.com>
Co-authored-by: Flora Feng <4florafeng@gmail.com>

tests/entrypoints/openai/responses/test_serving_responses.py

@@ -18,6 +18,9 @@ from openai.types.responses import (
     ResponseTextConfig,
     ResponseTextDeltaEvent,
 )
+from openai.types.responses import (
+    ResponseUsage as OpenAIResponseUsage,
+)
 from openai.types.responses.response_format_text_json_schema_config import (
     ResponseFormatTextJSONSchemaConfig,
 )
@@ -975,6 +978,7 @@ async def test_reasoning_tokens_counted_for_text_reasoning_model(monkeypatch):
         outputs=[completion],
         finished=True,
         num_cached_tokens=0,
+        num_cache_creation_tokens=3,
     )
     context.append_output(req_output)
 
@@ -995,6 +999,9 @@ async def test_reasoning_tokens_counted_for_text_reasoning_model(monkeypatch):
     )
 
     assert response.usage.output_tokens_details.reasoning_tokens == 1
+    assert response.usage.input_tokens_details.cache_write_tokens == 3
+
+    OpenAIResponseUsage.model_validate(response.usage.model_dump(mode="json"))
 
 
 class TestExtractAllowedToolsFromMcpRequests:

tests/entrypoints/unit_tests/test_context.py

@@ -682,6 +682,7 @@ def create_simple_context_output(
     prompt="Test prompt",
     prompt_token_ids=None,
     num_cached_tokens=0,
+    num_cache_creation_tokens=None,
     logprobs=None,
     finished=True,
 ):
@@ -707,6 +708,7 @@ def create_simple_context_output(
         ],
         finished=finished,
         num_cached_tokens=num_cached_tokens,
+        num_cache_creation_tokens=num_cache_creation_tokens,
     )
 
 
@@ -827,6 +829,7 @@ def test_simple_context_token_counting():
             token_ids=[10, 11],
             prompt_token_ids=[1, 2, 3, 4, 5],
             num_cached_tokens=2,
+            num_cache_creation_tokens=3,
         )
     )
     context.append_output(
@@ -835,12 +838,14 @@ def test_simple_context_token_counting():
             token_ids=[12],
             prompt_token_ids=[1, 2, 3, 4, 5],
             num_cached_tokens=2,
+            num_cache_creation_tokens=3,
         )
     )
 
     assert context.num_prompt_tokens == 5
     assert context.num_output_tokens == 3  # 2 + 1
     assert context.num_cached_tokens == 2
+    assert context.num_cache_creation_tokens == 3
 
 
 def test_simple_context_final_output():

vllm/entrypoints/openai/responses/context.py

@@ -189,6 +189,7 @@ class SimpleContext(ConversationContext):
         self.num_prompt_tokens = 0
         self.num_output_tokens = 0
         self.num_cached_tokens = 0
+        self.num_cache_creation_tokens = 0
         # todo num_reasoning_tokens is not implemented yet.
         self.num_reasoning_tokens = 0
         # not implemented yet for SimpleContext
@@ -204,6 +205,8 @@ class SimpleContext(ConversationContext):
             raise ValueError("SimpleContext only supports RequestOutput.")
         self.num_prompt_tokens = len(output.prompt_token_ids or [])
         self.num_cached_tokens = output.num_cached_tokens or 0
+        if output.num_cache_creation_tokens is not None:
+            self.num_cache_creation_tokens = output.num_cache_creation_tokens
         self.num_output_tokens += len(output.outputs[0].token_ids or [])
         if output.kv_transfer_params is not None:
             self.kv_transfer_params = output.kv_transfer_params

vllm/entrypoints/openai/responses/protocol.py

@@ -80,6 +80,7 @@ _INT64_MAX = 2**63 - 1
 
 class InputTokensDetails(OpenAIBaseModel):
     cached_tokens: int
+    cache_write_tokens: int
     input_tokens_per_turn: list[int] = Field(default_factory=list)
     cached_tokens_per_turn: list[int] = Field(default_factory=list)
 

vllm/entrypoints/openai/responses/serving.py

@@ -837,6 +837,7 @@ class OpenAIServingResponses(GenerateBaseServing):
             output_tokens=num_generated_tokens,
             total_tokens=num_prompt_tokens + num_generated_tokens,
             input_tokens_details=InputTokensDetails(
+                cache_write_tokens=getattr(context, "num_cache_creation_tokens", 0),
                 cached_tokens=num_cached_tokens,
                 input_tokens_per_turn=[
                     turn.input_tokens for turn in context.all_turn_metrics