GitHub Copilot GPT-6 models do not send selected reasoning effort #51850

Description

When using GPT-6 models through the GitHub Copilot provider, OpenCode does not include the selected reasoning effort in the outgoing /responses request.

OpenCode correctly records the selected variant, for example:

{
  "providerID": "github-copilot",
  "id": "gpt-6-luna",
  "variant": "max"
}

but the outgoing request does not contain a reasoning field:

{
  "model": "gpt-6-luna",
  "include": ["reasoning.encrypted_content"],
  "stream": true
}

The same happens with gpt-6-sol.

In comparison, gpt-5.6-luna with max correctly sends:

{
  "model": "gpt-5.6-luna",
  "reasoning": {
    "effort": "max",
    "summary": "auto"
  },
  "include": ["reasoning.encrypted_content"],
  "stream": true
}

Plugins

OpenCode version

2.0.18

Steps to reproduce

No response

Screenshot and/or share link

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Operating System

No response

Terminal

No response