Custom OpenAI provider 404 with empty URL (opencode.ai zen/go/v1)

[anmolxlight]

Bug Description

When using a custom OpenAI-type provider pointing to opencode.ai, requests fail with:

Note the empty URL — goose appears to be making a request to a relative/blank path.

Steps to Reproduce

1. Configure goose with a custom provider for opencode.ai using base_url
2. Run
   ( O)> ● new session · custom_opencode minimax-m2.5
   __) 20260413_42 · /home/ubuntu
   L L goose is ready
   ╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌ 0% 0/128k

● session closed · 20260413_42
3. Send any message
4. Error:

Expected Behavior

Requests should go to (verified working via curl with the same API key).

Provider Config

{
  "name": "custom_opencode",
  "engine": "openai",
  "base_url": "https://opencode.ai/zen/go/v1",
  "api_key_env": "CUSTOM_OPENCODE_API_KEY",
  "models": [
    {"name": "minimax-m2.5", "context_limit": 128000}
  ]
}

Investigation Findings

• with the same base_url + API key to returns 200
• The 404 error message has an empty URL — goose is constructing a request to a relative path with no host
• goose session starts successfully; error only occurs when sending a message
• The empty URL in the error suggests a routing bug in how goose constructs provider requests for custom OpenAI-type engines

Version

goose 1.30.0

[aravind4219]

Found the bug:

Goose takes that URL ("https://opencode.ai/zen/go/v1") and splits it into two parts:
-> Where to connect: https://opencode.ai
-> Which path to call: zen/go/v1

Now, when you send a message, goose needs to call the chat endpoint. In the OpenAI world, that endpoint is always at /chat/completions. So the full correct URL should be: https://opencode.ai/zen/go/v1/chat/completions

But goose had a blind spot. It knew that if the path was just v1, it should add /chat/completions. What it didn't account for was paths like zen/go/v1 , where v1 has something before it. So it thought zen/go/v1 was already a complete, final path and sent the request directly to:

https://opencode.ai/zen/go/v1 which is wrong, nothing is here

The server got a request at a path that doesn't exist and returned a 404 error. The "empty URL" you saw in the error message was just a misleading way of displaying that failed path , it wasn't truly empty, just wrong.