Gemini OpenAI-Compatible API Not Working - Uses Responses API Instead of Chat Completions

[samihalawa]

Gemini OpenAI-Compatible API Not Working - Uses Responses API Instead of Chat Completions

Description

Twenty CRM's OpenAI-compatible AI integration doesn't work with Google's Gemini API because it uses the Responses API (/responses) endpoint, but Gemini only supports the Chat Completions API (/chat/completions).

Steps to Reproduce

1. Configure OPENAI_COMPATIBLE_BASE_URL to https://generativelanguage.googleapis.com/v1beta/openai
2. Set OPENAI_COMPATIBLE_API_KEY to a valid Gemini API key
3. Add gemini-2.0-flash-exp to OPENAI_COMPATIBLE_MODELS
4. Try to use AI chat feature in Twenty CRM
5. Observe 404 Not Found error in container logs

Expected Behavior

Gemini should work as an OpenAI-compatible provider since it supports the /chat/completions endpoint.

Actual Behavior

Twenty makes requests to /responses endpoint which Gemini doesn't support, resulting in 404 errors.

Root Cause

In packages/twenty-server/src/engine/metadata-modules/ai/ai-models/services/ai-model-registry.service.ts:

private registerOpenAICompatibleModels(
  baseUrl: string,
  modelNamesString: string,
): void {
  const provider = createOpenAI({
    baseURL: baseUrl,
    apiKey: apiKey,
  });

  modelNames.forEach((modelId) => {
    this.modelRegistry.set(modelId, {
      modelId,
      provider: ModelProvider.OPENAI_COMPATIBLE,
      model: provider(modelId),  // ← PROBLEM: Uses Responses API
    });
  });
}

Proposed Solution

Use provider.chat(modelId) instead of provider(modelId) for OpenAI-compatible providers:

model: provider.chat(modelId),  // Uses /chat/completions instead of /responses

According to Vercel AI SDK v2.x documentation:

• provider(modelId) → Responses API (/responses)
• provider.chat(modelId) → Chat Completions API (/chat/completions)

Verification

I tested Gemini's /chat/completions endpoint directly and it works:

curl https://generativelanguage.googleapis.com/v1beta/openai/chat/completions \
  -H "Authorization: Bearer $API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model":"gemini-2.0-flash-exp","messages":[{"role":"user","content":"Hi"}]}'

But Twenty's container logs show it's calling /responses:

POST https://generativelanguage.googleapis.com/v1beta/openai/responses
→ 404 Not Found

Environment

• Twenty CRM version: Latest (as of December 2025)
• Vercel AI SDK: @ai-sdk/openai v2.0.30
• AI Provider: Google Gemini (OpenAI-compatible endpoint)

Impact

Users cannot use Gemini as an AI provider, which is a popular and cost-effective option with generous free tier.

Workaround

Use OpenAI, Anthropic, or xAI instead of Gemini until this is fixed.

[BOHEUS]

CC: @FelixMalfait @abdulrahmancodes

[thomtrp]

closing since AI is not released yet. Feel free to open a feature request if Gemini is still not supported @samihalawa!