From 3a4bf5c0d310b2066e76f5d8ccb1a04a1164ad8e Mon Sep 17 00:00:00 2001
From: umut-polat <52835619+umut-polat@users.noreply.github.com>
Date: Fri, 27 Feb 2026 17:34:58 +0000
Subject: [PATCH 1/2] Add missing @classmethod to ResponsesRequest model
 validators

The four model validators on ResponsesRequest (validate_background,
validate_prompt, check_cache_salt_support, function_call_parsing) were
missing the @classmethod decorator. All other model validators in the
codebase (completion, chat_completion protocols) use @classmethod
with @model_validator(mode='before') for consistency.

Signed-off-by: umut-polat <52835619+umut-polat@users.noreply.github.com>
---
 vllm/entrypoints/openai/responses/protocol.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/vllm/entrypoints/openai/responses/protocol.py b/vllm/entrypoints/openai/responses/protocol.py
index b0ffd0314792..ed60cf49b2f5 100644
--- a/vllm/entrypoints/openai/responses/protocol.py
+++ b/vllm/entrypoints/openai/responses/protocol.py
@@ -378,6 +378,7 @@ def is_include_output_logprobs(self) -> bool:
         )
 
     @model_validator(mode="before")
+    @classmethod
     def validate_background(cls, data):
         if not data.get("background"):
             return data
@@ -386,6 +387,7 @@ def validate_background(cls, data):
         return data
 
     @model_validator(mode="before")
+    @classmethod
     def validate_prompt(cls, data):
         if data.get("prompt") is not None:
             raise VLLMValidationError(
@@ -394,6 +396,7 @@ def validate_prompt(cls, data):
         return data
 
     @model_validator(mode="before")
+    @classmethod
     def check_cache_salt_support(cls, data):
         if data.get("cache_salt") is not None and (
             not isinstance(data["cache_salt"], str) or not data["cache_salt"]
@@ -404,6 +407,7 @@ def check_cache_salt_support(cls, data):
         return data
 
     @model_validator(mode="before")
+    @classmethod
     def function_call_parsing(cls, data):
         """Parse function_call dictionaries into ResponseFunctionToolCall objects.
         This ensures Pydantic can properly resolve union types in the input field.

From 0437db9d1679002185c5a6cb695e1970edbee869 Mon Sep 17 00:00:00 2001
From: umut-polat <52835619+umut-polat@users.noreply.github.com>
Date: Fri, 27 Feb 2026 17:37:10 +0000
Subject: [PATCH 2/2] Use VLLMValidationError in ResponsesRequest validators

Replace bare ValueError with VLLMValidationError in three places in
ResponsesRequest for consistency with the completion and chat_completion
protocols. VLLMValidationError includes the parameter name, giving
clients more actionable 400 responses.

Signed-off-by: umut-polat <52835619+umut-polat@users.noreply.github.com>
---
 vllm/entrypoints/openai/responses/protocol.py | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/vllm/entrypoints/openai/responses/protocol.py b/vllm/entrypoints/openai/responses/protocol.py
index ed60cf49b2f5..1ec88ccc3aa6 100644
--- a/vllm/entrypoints/openai/responses/protocol.py
+++ b/vllm/entrypoints/openai/responses/protocol.py
@@ -328,8 +328,9 @@ def to_sampling_params(
         # Also check text.format for OpenAI-style json_schema
         if self.text is not None and self.text.format is not None:
             if structured_outputs is not None:
-                raise ValueError(
-                    "Cannot specify both structured_outputs and text.format"
+                raise VLLMValidationError(
+                    "Cannot specify both structured_outputs and text.format",
+                    parameter="structured_outputs",
                 )
             response_format = self.text.format
             if (
@@ -383,7 +384,10 @@ def validate_background(cls, data):
         if not data.get("background"):
             return data
         if not data.get("store", True):
-            raise ValueError("background can only be used when `store` is true")
+            raise VLLMValidationError(
+                "background can only be used when `store` is true",
+                parameter="background",
+            )
         return data
 
     @model_validator(mode="before")
@@ -401,8 +405,9 @@ def check_cache_salt_support(cls, data):
         if data.get("cache_salt") is not None and (
             not isinstance(data["cache_salt"], str) or not data["cache_salt"]
         ):
-            raise ValueError(
-                "Parameter 'cache_salt' must be a non-empty string if provided."
+            raise VLLMValidationError(
+                "Parameter 'cache_salt' must be a non-empty string if provided.",
+                parameter="cache_salt",
             )
         return data