/model command does not show 1M context variants and resets opus[1m] to standard opus

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

The /model interactive picker does not display 1M context variants (e.g., opus[1m]). It only shows three options:

1. Default (recommended) — Sonnet 4.6
2. Opus — Opus 4.6
3. Haiku — Haiku 4.5

When a user has "model": "opus[1m]" configured in settings.json and uses /model to confirm or reselect the model, the setting is overwritten to plain "opus" (200K context), silently downgrading from 1M to 200K context.

This is related to but distinct from #36799 (which covers the setting reverting on session start). This issue specifically affects the /model slash command UI.

Steps to Reproduce

1. Set "model": "opus[1m]" in ~/.claude/settings.json
2. Start a new Claude Code session — status bar correctly shows Opus 4.6 (1M context)
3. Run /model
4. Observe: no 1M variants are listed — only Opus 4.6 (without [1m])
5. Select "Opus" or press Esc → the setting is overwritten to "opus", losing the 1M context

Expected Behavior

• The /model picker should include 1M context variants (e.g., Opus 4.6 (1M context)) as selectable options, at least for Max/Team/Enterprise plans where 1M is included
• Selecting Opus from the picker when opus[1m] is already configured should preserve the [1m] suffix
• At minimum, pressing Esc or selecting the already-active model should not downgrade the setting

What Should Happen?

The /model interactive picker should either:

1. Show separate 1M context options for eligible plans, or
2. Preserve the [1m] suffix when the user selects the same base model that's already configured

Claude Model

Opus

Is this a regression?

Not applicable (1M context is a recent GA feature)

Claude Code Version

2.1.87

Platform

Anthropic API

Operating System

macOS (Darwin 25.4.0)

Terminal/Shell

zsh

Plan

Max ($200)

Additional Information

Screenshot of the /model picker — no 1M option available:

The status bar correctly shows Opus 4.6 (1M context) when settings.json is manually configured, confirming the model itself works — only the picker UI is missing the option.