From dfd16b0b50e117106d808080f59143556daf9c2f Mon Sep 17 00:00:00 2001
From: mateo-berri <277851410+mateo-berri@users.noreply.github.com>
Date: Mon, 5 Oct 2026 16:37:38 -0700
Subject: [PATCH] fix(chatgpt): leave an empty string input for the backend to
 reject

OpenAI's Responses API answers 400 for input "", so wrapping it into a
one-message list would turn that error into a billed completion on the
Codex backend. Only a non-empty string becomes the user message.
---
 litellm/llms/chatgpt/responses/transformation.py     |  2 +-
 .../test_chatgpt_responses_transformation.py         | 12 ++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/litellm/llms/chatgpt/responses/transformation.py b/litellm/llms/chatgpt/responses/transformation.py
index 8c0261cd1f9..db5e43f65bc 100644
--- a/litellm/llms/chatgpt/responses/transformation.py
+++ b/litellm/llms/chatgpt/responses/transformation.py
@@ -82,7 +82,7 @@ class ChatGPTResponsesAPIConfig(OpenAIResponsesAPIConfig):
             litellm_params,
             headers,
         )
-        if isinstance(input, str):
+        if isinstance(input, str) and input != "":
             request["input"] = [{"role": "user", "content": [{"type": "input_text", "text": input}]}]
         base_instructions: Final = get_chatgpt_default_instructions()
         existing_instructions: Final = request.get("instructions")
diff --git a/tests/unit/llms/chatgpt/responses/test_chatgpt_responses_transformation.py b/tests/unit/llms/chatgpt/responses/test_chatgpt_responses_transformation.py
index f7a8033e2dd..f505ceb8da4 100644
--- a/tests/unit/llms/chatgpt/responses/test_chatgpt_responses_transformation.py
+++ b/tests/unit/llms/chatgpt/responses/test_chatgpt_responses_transformation.py
@@ -226,6 +226,18 @@ class TestChatGPTResponsesAPITransformation:
 
         assert request["input"] == list_input
 
+    def test_chatgpt_leaves_empty_string_input_for_the_backend_to_reject(self) -> None:
+        config: Final = ChatGPTResponsesAPIConfig()
+        request: Final = config.transform_responses_api_request(
+            model="chatgpt/gpt-6.1-sol",
+            input="",
+            response_api_optional_request_params={},
+            litellm_params=GenericLiteLLMParams(),
+            headers={},
+        )
+
+        assert request["input"] == ""
+
     @pytest.mark.parametrize(
         "model_name",
         [