[BUG] claude-opus-4-6 uses 200K context window instead of 1M

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?

Description

When selecting model claude-opus-4-6 via /model claude-opus-4-6, Claude Code applies a 200K token context window. Per Anthropic's model documentation, Opus 4.6 supports a 1M token context window.

Steps to reproduce

1. Run /model claude-opus-4-6
2. Observe the context window is 200K tokens

Expected behavior

Context window should be 1M tokens for claude-opus-4-6, matching the published model specification.

Actual behavior

Context window is set to 200K tokens.

Environment

• Claude Code version: 2.1.231
• OS: macOS (Darwin 25.3.0)

What Should Happen?

1M Context window

Error Messages/Logs

Steps to Reproduce

<img width="1114" height="49" alt="Image" src="https://github.com/user-attachments/assets/1706b068-4520-4e9f-92df-2a3760655c64" />

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

v2.1.231

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

_No response_