[BUG] Opus 4.6 1M context disappears from model picker, replaced by Opus 4.6 200k; default silently changes to Sonnet

Preflight Checklist

• [x] Searched existing issues (related: #45978)
• [x] Single bug report
• [x] Latest version of Claude Code

What's Wrong?

Date: 2026-04-10
Plan: Claude Max

Today the Claude Code model picker changed in a way that prevents users from selecting Opus 4.6 with 1M context:

1. Default silently switched from "Opus 4.6 (1M context)" to "Sonnet 4.6 (200k)". Sessions that were running on Opus 1M were downgraded mid-session without user action.

1. New entry appeared: "Opus 4.6 200k context" is now listed in /model picker alongside the existing Sonnet/Haiku entries.

1. Opus 4.6 1M context cannot be pinned: even when manually selecting the 1M variant, it disappears from the list on the next /model invocation or model switch. There is no way to keep Opus 1M as a persistent choice.

Steps to Reproduce

1. Start a Claude Code session with Opus 4.6 (1M context) previously set as default.
2. Observe that the default shown is now Sonnet 4.6 (200k).
3. Run /model — note that "Opus 4.6 200k" is listed but "Opus 4.6 1M" is not selectable / disappears after selection.

Expected

• Opus 4.6 with 1M context remains available and persistently selectable.
• Default should not change without user action.

Actual

• Default changed from Opus/1M → Sonnet/200k without user input.
• Opus/1M is not reliably selectable.
• New Opus/200k variant appeared.

Environment

• Platform: macOS (darwin 24.6.0)
• Claude Code CLI
• Plan: Claude Max

<img width="569" height="115" alt="Image" src="https://github.com/user-attachments/assets/802c9621-ca25-4560-8e1c-9dd490afdd64" />