[BUG] Model selection shows Opus 4.6 but chat reports 4.5

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

When I run /model, the checkmark is on Opus 4.6. But when I (vscode UI) chat with the model and ask what model it is, it says it's Claude-Opus-4.5. The UI and the actual model being used don't match.

What Should Happen?

When /model shows Opus 4.6 selected, the (vscode UI) chat should use Opus 4.6.

Error Messages/Logs

$ claude config get model
Welcome to Opus 4.6

Model self-reports: "You are powered by the model named Opus 4. The exact model ID is Claude-Opus-4.5."

Steps to Reproduce

1. Open Claude Code in VSCode
2. Run /model and select Opus 4.6
3. Start a new session
4. Run /model again - checkmark shows Opus 4.6 ✓
5. Ask in (vscode UI) chat: "what model are you?"
6. Model responds: "Claude Opus 4, model ID: Claude-Opus-4.5"

Claude Model

None

Is this a regression?

I don't know

Last Working Version

Unknown

Claude Code Version

claude --version 2.1.42 (Claude Code)

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

VS Code integrated terminal

Additional Information

OS Version: Linux 6.xxx-generic
IDE: VSCode native extension

Both UI (/model) and CLI (claude config get model) confirm
Opus 4.6 is selected, but the model's system context shows
Claude-Opus-4.5. The configuration isn't being applied to
the actual API call.