`400 Unsupported parameter: 'messages'.` error on OpenAI Compatible Azure deployment of GPT-5

[jmmfcoutinho]

App Version

3.25.10

API Provider

OpenAI Compatible

Model Used

gpt-5

Roo Code Task Links (Optional)

No response

🔁 Steps to Reproduce

VSCode on Windows with WSL.
gpt-5 (not chat) deployment on Azure.

BASE URL: https://.openai.azure.com/openai/responses?api-version=2025-04-01-preview
MODEL: gpt-5
USE AZURE: Yes
SET API VERSION: Yes --> 2025-04-01-preview
ENABLE REASONING EFFORT: Yes --> High
USE CUSTOM TEMPERATURE: Yes --> 1

I just sent a simple "hi" message and got this error:

400 Unsupported parameter: 'messages'. In the Responses API, this parameter has moved to 'input'. Try again with the new parameter. See the API documentation for more information: https://platform.openai.com/docs/api-reference/responses/create.

gpt-5 (non-chat), the one where you can set the reasoning effort and other parameters, uses the responses API. It seems that the request sent through Roo is using chat completions parameters (that's my guess, but I have no clue)

💥 Outcome Summary

Expected API request to work, but got an error that implies wrong parameters are being sent to the responses API used by the GPT-5 (non-chat) model.

📄 Relevant Logs or Errors (Optional)

[roomote]

Hi! I'm here to help out the maintainers and am going to see if I can fix this issue.

It looks like the problem is that Roo Code is using the traditional chat completions API parameters (with "messages") when it should be using the new responses API format (with "input") for GPT-5 non-chat models on Azure. I'll investigate the codebase and work on a fix to properly support the responses API endpoint.

Thanks for the detailed bug report with the specific error message - that's very helpful!

[SannidhyaSah]

@roomote-agent can you create a pr to fix this issue ?

[roomote]

Hi @SannidhyaSah! I'm on it. I'll create a PR to fix the Azure GPT-5 responses API compatibility issue. The problem is that Roo Code is sending "messages" parameter when it should be sending "input" for the GPT-5 non-chat model that uses the responses API endpoint.

I'll investigate the codebase and implement the necessary changes to properly support the Azure GPT-5 responses API format.

[roomote]

Hi @SannidhyaSah!

I've created PR #6893 to fix the GPT-5 Azure responses API issue: #6893

The fix detects when GPT-5 models are being used with Azure and automatically switches to use the responses API with the correct "input" parameter format instead of the chat completions "messages" parameter.

The PR includes:

• Detection for GPT-5 models when using Azure OpenAI
• Support for the responses API endpoint and parameters
• Proper handling of GPT-5 specific features (reasoning effort, verbosity, etc.)
• Comprehensive test coverage

CI checks are currently running. Once they pass and the PR is reviewed, this should resolve the issue you were experiencing.

[arnabbiswas1]

I have been able to use it with the following BASE URL:

https://<>.openai.azure.com/openai/deployments/gpt-5/chat/completions?api-version=2025-01-01-preview

"gpt-5" is the deployment name. But I am finding it extremely slow.

API Provider: OpenAI Compatible
BASE URL: https://<>.openai.azure.com/openai/deployments/gpt-5/chat/completions?api-version=2025-01-01-preview
Model: gpt-5 (This is the deployment name)
Use Azure: Selected
Enable Reasoning Effort: Selected
Model Reasoning Effort: Low
Output Verbosity: Low

Question:

• Am I missing something that can explain the slowness?
• How to change the reasoning to minimal?

[isoamyl50]

• Am I missing something that can explain the slowness?

I got slow responses too, even for response with error and called using multiple clients (not just Roo code). I think that the slowness comes from the API.

You can verify this by manually sending the API request using cURL or postman and time it.

• How to change the reasoning to minimal?

Roomote is currently working on improving GPT-5 support. Check out PR #6893 for more detail. You can add a comment there to add more context to Roomote about the new reasoning level for GPT-5.