Composer 2.5 error "This model does not support custom API keys"

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Hey, thanks for the report. This isn’t a bug, it’s the current by design behavior.

Composer (1, 1.5, 2, 2.5) are Cursor’s own models, and they don’t work with BYOK keys. When OpenAI API Key / Override OpenAI Base URL is enabled, the key gets attached to all requests, including Composer, so you’ll see the error “This model does not support custom API keys”. On Auto, this doesn’t happen because the key isn’t attached to those requests.

Workaround:

  • Turn off the OpenAI API Key toggle with Cmd+Shift+0 while using Composer. This won’t remove your key or URL, so you won’t need to re-enter them.
  • Or use Auto.

What you described in Expected Behavior, per-model routing so the key is automatically removed for Cursor models, is a known QoL improvement. It’s on our radar, but there’s no ETA yet.