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[BUG]: GitHub Copilot Responses API routing for GPT-5+ #5866
Description
Problem
When using the github-copilot provider, GPT-5+ models are currently routed through the Chat API. This prevents users from enabling Responses-API-only controls (eg. reasoningEffort, reasoningSummary) for those models, even when they are supported by the model and useful for agent behavior tuning.
This is especially noticeable for github-copilot/gpt-5.* where users expect to be able to configure reasoning parameters similarly to other OpenAI-compatible providers.
Proposed Solution
Add an opt-in provider option to route supported Copilot models through the Responses API:
- New config flag:
provider.github-copilot.options.useResponsesApi: true - Behavior:
- Always route
codex*models throughsdk.responses(modelID)(existing behavior) - If
useResponsesApiis enabled and the model is GPT-5 or later, route throughsdk.responses(modelID) - Otherwise, default to
sdk.chat(modelID)(no behavior change by default)
- Always route
Example config:
{
"provider": {
"github-copilot": {
"options": {
"useResponsesApi": true
}
}
}
}Future (Deprecation)
Once GitHub Copilot / VS Code enables Responses API usage broadly (the VS Code setting is currently labeled Experimental), this option can likely be deprecated and/or defaulted on for supported models to reduce configuration surface area.
References
Current status of supported API route for provider github-copilot:
| Model | API Route |
|---|---|
| gpt-4.1 | chat |
| gpt-4o | chat |
| gpt-5 | responses |
| gpt-5-codex | responses |
| gpt-5-mini | chat |
| gpt-5.1 | responses |
| gpt-5.1-codex | responses |
| gpt-5.1-codex-max | responses |
| gpt-5.1-codex-mini | responses |
| gpt-5.2 | responses |
- VS Code UI (settings) relevant to this feature:
GitHub > Copilot > Chat: Use Responses Api(Experimental)GitHub > Copilot > Chat: Responses Api Reasoning Effort(Experimental)GitHub > Copilot > Chat: Responses Api Reasoning Summary(Experimental)
Screenshot of the VS Code settings panel showing the above Copilot settings.
Environment
- Repo:
sst/opencode(dev) - Platform observed: Windows (but the behavior is provider/model routing specific, not OS-specific)
Activity
github-actions commentedon Dec 20, 2025
This issue might be a duplicate of existing issues. Please check:
Feel free to ignore if none of these address your specific case.
[-]Feature: opt-in GitHub Copilot Responses API routing for GPT-5+[/-][+]Feature: GitHub Copilot Responses API routing for GPT-5+[/+]jbuckmccready commentedon Jan 4, 2026
Is this something Github changed recently? I had reasoningEffort working with GPT 5.2 and now it no longer works (no change to configuration on my end).
christso commentedon Jan 5, 2026
@jbuckmccready This is a change in OpenCode, not GitHub.
Commit f1bb587 (merged December 1st) broke reasoning support for GPT-5.2 and other non-Codex GPT-5 models. The change incorrectly assumed only Codex models support reasoning, so it only routes models with "codex" in the name to the API that supports
reasoningEffort. Everything else goes to a different API that doesn't support it.GPT-5.2 was working with reasoning before this commit. There's a PR to fix it.
@rekram1-node should this be reclassified from feature to a bug? I previously thought it was a feature until I discovered it was working previously.
[-]Feature: GitHub Copilot Responses API routing for GPT-5+[/-][+][BUG]: GitHub Copilot Responses API routing for GPT-5+[/+]SamPeng87 commentedon Jan 13, 2026
I think your PR fix still requires the above parameters to activate the thinking mode. Is my understanding correct?
christso commentedon Jan 16, 2026
@SamPeng87 Yes, your understanding is correct. This PR fixes the error that occurs when reasoning is enabled, but you still need to configure the parameters (reasoningEffort, reasoningSummary, include) in your opencode.json to activate thinking mode.
scratchmex commentedon Jan 20, 2026
We need this option for OpenAI compatible models as well