GitHub Copilot compatibility issue with streaming responses containing empty choices chunks

Description

Description:

When using OpenCode Go as an OpenAI-compatible Chat Completions endpoint with GitHub Copilot in VS Code, some models fail because the streaming response contains multiple chunks with an empty choices array before the actual content chunks.

The same model works correctly with non-streaming requests.

Environment:

• Client: VS Code GitHub Copilot extension
• Provider: OpenCode Go
• Endpoint: https://opencode.ai/zen/go/v1/chat/completions
• Model: muse-spark-1.2-contributor

Issue:

A non-streaming request returns a valid OpenAI Chat Completions response with choices:

{
"object": "chat.completion",
"choices": [
{
"message": {
"role": "assistant",
"content": "Hello!"
}
}
]
}

However, when stream=true is used, the response starts with multiple chunks containing an empty choices array:

data: {"object":"chat.completion.chunk","choices":[]}

before the actual content chunks:

data: {"choices":[{"index":0,"delta":{"content":"Hello!"}}]}

GitHub Copilot fails to parse this streaming response and returns:

Response contained no choices.

Expected behavior:

Streaming responses should follow the OpenAI Chat Completions streaming format and avoid sending empty choices chunks, or ensure compatibility with clients that require valid choices in streaming chunks.

Actual behavior:

OpenCode Go sends several empty choices chunks before the assistant content, causing compatibility issues with GitHub Copilot.

Additional information:

The same endpoint and model work correctly when stream=false is used. This appears to be a streaming response formatting compatibility issue rather than an authentication or model availability issue.

Possible fix:

Filter out empty choices chunks in the streaming adapter or ensure every emitted chunk follows the expected OpenAI-compatible streaming format.

Plugins

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OpenCode version

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Steps to reproduce

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Screenshot and/or share link

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Operating System

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Terminal

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