Session title generation fails for Claude models via Antigravity provider (OpenCode)

[edxeth]

Is it a request payload issue?

• No, it's another issue.

Describe the bug
OpenCode session title generation fails when using Claude models through the Antigravity provider. Sessions show "New session - 2026-02-02T13:00:43.469Z" instead of descriptive titles like "Friendly greeting".

This affects only Claude models routed through CLIProxyAPI. Gemini and OpenAI models through the same proxy generate titles correctly.

Root Cause Analysis:
After investigating both OpenCode and CLIProxyAPI codebases, the issue appears related to:

1. Recent refactor (commit ac802a4) that removed selectInstructions and OpenCode User-Agent handling
2. Streaming response translation for small/simple requests - the title agent sends a minimal streaming request that may not be properly translated back to Claude format
3. The gzip fix in code_handlers.go:176-195 attempted to address this but doesn't fully resolve it

OpenCode's title generation flow:

1. packages/opencode/src/session/summary.ts:summarizeMessage() triggers the "title" agent
2. Uses LLM.stream() with a small model (defaults to Claude Haiku or similar)
3. Request goes through CLIProxyAPI → Antigravity backend → response translation
4. The translated response either returns empty or malformed, causing title generation to silently fail

CLI Type
Antigravity (Claude Code compatible)

Model Name

• gemini-claude-opus-4-5-thinking
• gemini-claude-sonnet-4-5-thinking
• gemini-claude-sonnet-4-5

(Any Claude model routed through Antigravity provider)

LLM Client
OpenCode v1.1.48

Request Information
The title generation request is a simple streaming request to /v1/messages with:

• Small payload (just a text summarization prompt)
• stream: true
• Uses the "title" agent system prompt

The request originates from OpenCode's Vercel AI SDK integration hitting http://localhost:8317/v1/messages.

Expected behavior
Session titles should be generated and displayed (e.g., "Friendly greeting", "TypeScript math utility functions") instead of "New session - {timestamp}".

OS Type

• OS: Ubuntu 24.04.3 LTS (WSL2)
• Architecture: x64

Additional context
Workaround: Setting "small_model": "google/gemini-3-flash-preview" in OpenCode's opencode.json bypasses the issue by routing title generation requests directly to Google instead of through CLIProxyAPI.

Relevant CLIProxyAPI files to investigate:

• sdk/api/handlers/claude/code_handlers.go - handleStreamingResponse() and handleNonStreamingResponse()
• internal/runtime/executor/claude_executor.go - ExecuteStream()
• internal/translator/claude/gemini/claude_gemini_response.go - streaming response translation

The issue likely started after recent refactors to the translator layer. The fact that the gzip fix specifically mentions "title generation" suggests awareness of this issue area.

[xitex]

incorrect model names i think try claude-opus-4-5-thinking
here is example:
claude-sonnet-4-5-thinking": { "name": "claude-sonnet-4-5-thinking", "family": "unknown", "reasoning": true, "tool_call": true, "attachment": true, "modalities": { "input": ["text", "image", "pdf"], "output": ["text"] }, "cost": { "input": 0, "output": 0 }, "limit": { "context": 200000, "output": 64000 }, "interleaved": { "field": "reasoning_content" }, "provider": { "npm": "@ai-sdk/anthropic" } },

[edxeth]

@xitex the model name is correctly set.

[ardzz]

@xitex may i see your models opencode config? or where i can get the models template?