Allow disabling Responses API for OpenAI-compatible servers with gpt-5-like model aliases

[Atompapst]

Before submitting your bug report

• I've tried finding an answer on the Continue docs site
• I'm not able to find an open issue that reports the same bug
• I've seen the troubleshooting guide on the Continue Docs

Relevant environment info

- OS: Linux CachyOS
- Continue version: 2.0
- IDE version: Rider 2026.1.4
- Model: openai
- config:
  
name: Local Config
version: 1.0.0
schema: v1

models:
  - name: gpt-5.5
    provider: openai
    model: gpt-5.5
    apiBase: https://chatgpt.myCompany.de/api/
    apiKey: xxxx
    useLegacyCompletionsEndpoint: false
 

Description

Problem

When using the openai provider with a custom OpenAI-compatible API and a model named gpt-5.5, Continue automatically uses the Responses API endpoint:

POST /responses

This fails because the backend only supports OpenAI-compatiblnAI provider forces /responses for custom gpt-5-like model names on OpenAI-compatible APIse Chat Completions:

POST /chat/completions

The model name is a custom/internal alias and does not imply that the backend supports the OpenAI Responses API.

Evidence

This fails:

curl -i https://chatgpt.myCompany.de/api/responses
-H "Authorization: Bearer xxx"
-H "Content-Type: application/json"
-d '{"model":"gpt-5.5","input":"Hallo"}'

Result:

HTTP 405 Method Not Allowed

This works:

curl -i https://chatgpt.myCompany.de/api/chat/completions
-H "Authorization: Bearer xxx"
-H "Content-Type: application/json"
-d '{
"model": "gpt-5.5",
"messages": [{"role": "user", "content": "Hallo"}]
}'

Result:

HTTP 200 OK

continue/core/llm/llms/OpenAI.ts

Lines 221 to 223 in d0a3c0b

	public isOSeriesOrGpt5PlusModel(model?: string): boolean {
	return !!model && (!!model.match(/^o[0-9]+/) || !!model.match(/gpt-[5-9]/));
	}

Expected behavior

There should be a config option to disable the Responses API for OpenAI-compatible backends, e.g.

useResponsesApi: false

or Continue should only use /responses automatically for the official OpenAI API, not for arbitrary apiBase values.

useLegacyCompletionsEndpoint: false does not solve this, because the issue is not /completions vs /chat/completions, but /responses vs /chat/completions.

To reproduce

No response

Log output