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bug(copilot): gpt-5.x-mini variants incorrectly routed to Responses API #15823
Description
Summary
shouldUseCopilotResponsesApi in packages/opencode/src/provider/provider.ts only excludes models whose ID starts with gpt-5-mini:
function shouldUseCopilotResponsesApi(modelID: string): boolean {
return isGpt5OrLater(modelID) && !modelID.startsWith("gpt-5-mini")
}This means any minor-versioned mini model — gpt-5.1-mini, gpt-5.2-mini, etc. — is incorrectly routed to the Responses API instead of the Chat Completions API, because those IDs don't start with gpt-5-mini.
Impact
| Model ID | Current behaviour | Expected |
|---|---|---|
gpt-5-mini |
✅ Chat API | ✅ Chat API |
gpt-5.1-mini |
❌ Responses API | ✅ Chat API |
gpt-5.2-mini |
❌ Responses API | ✅ Chat API |
gpt-5 |
✅ Responses API | ✅ Responses API |
gpt-5.1 |
✅ Responses API | ✅ Responses API |
Routing a mini model to the Responses API can cause invalid_request_body errors or unexpected behaviour, since mini models are not expected to support the Responses API endpoint.
Expected fix
Broaden the exclusion to any model in the gpt-5 family that contains mini anywhere in the name, to stay forward-compatible with OpenAI's major.minor naming convention.
Activity
github-actions commentedon Mar 3, 2026
This issue might be a duplicate of existing issues. Please check:
gpt-5-mininot being supported via the Responses API — this issue extends that same problem togpt-5.x-mini(minor-versioned) variants that weren't covered by the initial exclusion check.Juhwa-Lee1023 commentedon Mar 3, 2026
Not a duplicate of #4943.
This fork's dev branch has diverged from upstream (sst/opencode) and implements its own shouldUseCopilotResponsesApi function independently. The upstream fix at f1bb5870 took a completely different approach — switching the routing condition from gpt-5 string inclusion to codex inclusion — so it is not applicable here.
The bug in this fork is specific to its own shouldUseCopilotResponsesApi logic: it excludes only models whose ID starts with gpt-5-mini, which misses minor-versioned mini variants like gpt-5.1-codex-mini that already exist in this codebase. PR #15818 fixes exactly that.
github-actions commentedon May 3, 2026
To stay organized issues are automatically closed after 60 days of no activity. If the issue is still relevant please open a new one.