GitHub Copilot grok-4.5 fails: not accessible via /chat/completions #42759

Description

Selecting grok-4.5 through the GitHub Copilot provider fails immediately with:

GitHub Copilot only serves grok-4.5 on /responses. OpenCode still routes grok-* to /chat/completions. Same class of bug as #2758 (gpt-5-codex). The Copilot plugin currently sends only GPT-5+ models to Responses; grok-4.5 falls through to chat completions.

The same Copilot account can use Grok 4.5 in VS Code.

Plugins

None.

OpenCode version

1.16.2

Steps to reproduce

1. /connect → GitHub Copilot
2. /model → github-copilot/grok-4.5
3. Send any prompt

Screenshot and/or share link

N/A. Error text: model "grok-4.5" is not accessible via the /chat/completions endpoint

Operating System

Windows 10

Terminal

OpenCode desktop