Vercel AI gateway not working

[Strift]

What happened?

I'm unable to connect to the Vercel AI Gateway using a custom endpoint. Any guidance would be appreciated.

Describe the bug
I am trying to configure LibreChat to use the Vercel AI Gateway as a custom endpoint, as documented here.

I have added the required configuration to my librechat.yaml file and set the corresponding API key in my .env file.

When using fetch: true, all models appear in the model selection dropdown. However, I receive a 405 error when attempting to send a message (see error below).

My librechat.yaml configuration

endpoints:
  custom:
    - name: "Vercel"
      apiKey: "${VERCEL_AI_GATEWAY_API_KEY}"
      baseURL: "https://ai-gateway.vercel.sh/v1"
      titleConvo: false
      models:
        default:
          - "openai/gpt-5-mini"
          - "google/gemini-2.5-flash"
          - "deepseek/deepseek-v3.1"
          - "anthropic/claude-3-haiku"
        fetch: true

Environment

I'm using the latest version as of today, v0.8.0-rc4, running in Docker via docker compose.

Version Information

git rev-parse HEAD gave:

68c9f66

Steps to Reproduce

1. Create a librechat.yaml file with the configuration below.
2. Add VERCEL_AI_GATEWAY_API_KEY="<your-key>" to the .env file.
3. Restart the LibreChat application (docker-compose down && docker-compose up -d).
4. Open the web UI and select a model in the Vercel dropdown
5. Send "hi"

What browsers are you seeing the problem on?

Chrome

Relevant log output

The UI displays: 
> Something went wrong. Here's the specific error message we encountered: An error occurred while processing the request: 405 status code (no body)

**Logs**

2025-09-20T05:10:37.149Z debug: [BaseClient] userMessage
{
  messageId: "b953fb81-aab5-47de-952a-7c047a7cfada",
  parentMessageId: "00000000-0000-0000-0000-000000000000",
  conversationId: "ff11482b-eaba-43c0-abb2-f4aac41aa314",
  sender: "User",
  text: "hi",
  isCreatedByUser: true,
  tokenCount: 5,
}
2025-09-20T05:10:37.199Z debug: [saveConvo] api/app/clients/BaseClient.js - saveMessageToDatabase #saveConvo
2025-09-20T05:10:38.026Z debug: Memory Agent processed memory successfully
["{\"type\":\"text\",\"text\":\"Hello! How can I assist you today?\"}"]
2025-09-20T05:10:38.027Z error: [api/server/controllers/agents/client.js #sendCompletion] Operation aborted 405 status code (no body)
2025-09-20T05:10:38.027Z error: [api/server/controllers/agents/client.js #sendCompletion] Unhandled error type 405 status code (no body)

Screenshots

No response

Code of Conduct

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[danny-avila]

Seems to be working well for me:

Same exact config

[danny-avila]

@Strift which model are you using?

[Strift]

It seems it was due to the extra parameters that the UI was including. I removed them, and now it is working.

Apologies for the false report. That being said, the error messages could be more helpful with custom endpoints. (Maybe I'm not looking at the right place?)

[danny-avila]

I agree it could be more helpful but in this case, this is what Vercel is providing us