Question: How does opencode work with Claude Code OAuth tokens when AI SDK fails? #417

Hi! I'm trying to understand how opencode successfully uses Claude Code OAuth tokens with the Anthropic API, as I'm getting restrictions when trying to replicate the same approach.

I've been studying opencode's implementation to understand how it integrates with Claude Code OAuth. Based on my analysis of the codebase, opencode uses:

• @ai-sdk/anthropic package
• Standard https://api.anthropic.com/v1/messages endpoint
• Custom fetch function with Bearer ${accessToken} authorization
• anthropic-beta: oauth-2025-04-20 header
• Removes x-api-key header

This is exactly implemented in /packages/opencode/src/provider/provider.ts lines 42-71.

When I try to replicate this exact approach using Claude Code OAuth tokens, I get this error:

{
    "type": "error",
    "error": {
        "type": "invalid_request_error",
        "message": "system: This credential is only authorized for use with Claude Code and cannot be used for other API requests."
    }
}

So I have a few questions:

1. How does opencode bypass this restriction? The error suggests Claude Code OAuth tokens are restricted to "Claude Code" only, but opencode successfully uses them.
2. Is there a special endpoint or configuration? Does opencode use a different API endpoint, special headers, or application registration that allows it to work?
3. Application whitelisting? Is opencode specifically whitelisted by Anthropic to use Claude Code OAuth tokens?
4. Token scopes or format? Are there specific OAuth scopes or token formats that opencode requests that differ from standard Claude Code tokens?

So far I've tried

• Used identical headers and fetch configuration as opencode
• Tried console.anthropic.com endpoint instead of api.anthropic.com
• Verified token format matches opencode's auth.json structure
• Used same AI SDK version and configuration

I expected to be able to use Claude Code OAuth tokens with the AI SDK following opencode's implementation pattern, since opencode clearly demonstrates this is possible.

Environment Details

• Node.js v22.17.0
• @ai-sdk/anthropic v1.2.12
• ai SDK (latest)

Any insights into how opencode's Anthropic integration works would be greatly appreciated! The codebase shows it's using standard AI SDK patterns, but there must be something special about how it's configured or registered with Anthropic.

Thanks in advance guys, and great job on the product. I've loved using it.