GitHub Copilot: Claude models newer than opus-4.7 never show thinking (adaptive display omitted)

[afriemann]

Description

GitHub Copilot Claude models newer than opus-4.7 (e.g. claude-sonnet-5, claude-opus-4.8) never show thinking/reasoning content in the UI, even with thinking enabled — the reasoning part is emitted but its text is empty.

Root cause: packages/opencode/src/plugin/github-copilot/models.ts only sets thinking.display: "summarized" for models matching the literal string opus-4.7, when building the adaptive-thinking variant for Copilot's /v1/messages endpoint. Anthropic omits thinking content by default for any adaptive-only Claude model newer than that (major version >4, or 4.7+), so the override never gets applied to sonnet-5, opus-4.8, or any future model in that range.

Related: #36120 reports the same symptom for opus-4.8 specifically; this is the general root cause behind it.

OpenCode version

1.18.25 (also reproduces on current dev)

Steps to reproduce

1. Configure the github-copilot provider with a modern Claude model, e.g. claude-sonnet-5 or claude-opus-4.8
2. Start a session with a high/max reasoning variant
3. Ask a question that would trigger reasoning
4. Thinking never appears in the UI, even with the thinking display toggled on

Confirmed via a live A/B test: same prompt against the current code returns a reasoning part with text: "" (empty); with thinking.display forced to "summarized" it returns real reasoning content.

Screenshot and/or share link

N/A — confirmed via raw JSON event output (--format json), not a rendering-only issue.

[github-actions]

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

• claude opus 4.8 thru github copilot doesn't show thinking #36120: Same symptom (thinking not shown for Claude via GitHub Copilot) — this issue claims to identify the general root cause behind that report.