[FEATURE]: Support for Claude Opus 4.6 Fast Mode

[Tetrahedrite]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

First, thank you for maintaining this project. I really appreciate all your work.

I wanted to bring to your attention that both Anthropic and GitHub Copilot have recently announced experimental support for Fast Mode with the Claude Opus 4.6 model. I would love to see this capability available in OpenCode, but it doesn’t appear that such a feature or commit exists yet, and I haven’t seen any related issue requests.

It would be fantastic if this functionality could be supported.

Thank you!

[github-actions]

This issue might be a duplicate of existing feature requests. Please check:

• [FEATURE]: Add support of Claude Opus 4.6 #12323: [FEATURE]: Add support of Claude Opus 4.6 - General Opus 4.6 model support
• [FEATURE]: Add Claude Opus 4.6 support for GitHub Copilot provider #12504: [FEATURE]: Add Claude Opus 4.6 support for GitHub Copilot provider - Specifically addresses Opus 4.6 for GitHub Copilot
• Support adaptive thinking for Claude Opus 4.6 #12485: Support adaptive thinking for Claude Opus 4.6 - Related Opus 4.6 feature

Fast Mode is a specific capability of Opus 4.6. Once Opus 4.6 support is added (especially for GitHub Copilot), the Fast Mode feature would likely be available as part of that implementation.

[dragonhuntr]

bump on this

[utapyngo]

There is an issue on this at models.dev: anomalyco/models.dev#833

[Tetrahedrite]

@utapyngo Thanks for letting me know. I didn't realize this was an issue with that repository. I'll go ahead and close this.

[utapyngo]

@utapyngo Thanks for letting me know. I didn't realize this was an issue with that repository. I'll go ahead and close this.

Actually I would keep this open since it seems that changes to opencode are also required. I tried adding this to my opencode.json:

  "provider": {
    "github-copilot": {
      "models": {
        "claude-opus-4.6-fast": {
          "id": "claude-opus-4.6-fast",
          "name": "Claude Opus 4.6 (fast mode)",
          "family": "claude-opus",
          "attachment": true,
          "reasoning": true,
          "tool_call": true,
          "temperature": true,
          "release_date": "2026-02-07",
          "limit": {
            "context": 200000,
            "output": 64000
          }
        }
      }
    }

The model appeared in the list but the server keeps responding with "The requested model is not supported".

[Tetrahedrite]

@utapyngo

(Note: I'm writing this from memory without my work environment in front of me, so some details might not be perfectly accurate.)

Yesterday, after briefly doing some LLM-assisted research and analyzing the microsoft/vscode-copilot-chat extension, I discovered that the Copilot domain and /models endpoint used by OpenCode simply do not expose the claude-opus-4.6-fast model at all.

When I requested /models against the domain OpenCode uses (api.githubcopilot.com), the claude-opus-4.6-fast model was not in the list. As a result, all requests fail with the message: "The requested model is not supported."

However, the model selector in VSCode's official Copilot Chat extension clearly includes Opus 4.6 Fast Mode. Digging into the source code based on that, I found that VSCode actually sends requests to a different domain: api.individual.githubcopilot.com. The /models endpoint on this domain does expose the Fast Mode model.

I still need to investigate this further, but I suspect the authentication workflow itself might be different, and it's unclear if GitHub Copilot intended this behavior or not. Just to be sure, I even tried signing out of GitHub Copilot in OpenCode and authenticating again, but the model still didn't appear in the list.

[utapyngo]

However, the model selector in VSCode's official Copilot Chat extension clearly includes Opus 4.6 Fast Mode. Digging into the source code based on that, I found that VSCode actually sends requests to a different domain: api.individual.githubcopilot.com. The /models endpoint on this domain does expose the Fast Mode model.

So we need to reopen this issue.

[Tetrahedrite]

@utapyngo Okay, I just don't want to bother them. But come to think of it, GitHub Copilot is one of the official providers for OpenCode, isn't it? So I think I need to reopen this. They might even be able to request GitHub Copilot to support Fast Mode for OpenCode as well.

[Xynonners]

Would love to see this for GPT 5.4 fast mode as well!