sonnet[1m] and fable[1m] model aliases do not apply 1M context window (only opus[1m] works)

Description

The [1m] model alias suffix (documented at https://code.claude.com/docs/en/model-config) works correctly for Opus, but does not apply the 1M context window for Sonnet or Fable, even though both models support 1M context at the API level (per https://platform.claude.com/docs/en/about-claude/models/overview).

Steps to reproduce

1. Run /model opus[1m]

• Confirmation: "Set model to Opus 4.8 (1M context)" ✅ label present
• Status line reports total context window as 1.0M ✅

1. Run /model sonnet[1m]

• Confirmation: "Set model to Sonnet 5" ❌ no "(1M context)" label
• Status line reports total context window as 200.0k ❌

1. Run /model fable[1m]

• Same result as Sonnet: confirmation drops the "(1M context)" label, status line stays at 200.0k

Expected behavior

sonnet[1m] and fable[1m] should apply a 1,000,000 token context window and report it in the /model confirmation and in the context_window.total_tokens field passed to the status line, consistent with opus[1m].

Actual behavior

Only opus[1m] actually engages the 1M context window. sonnet[1m] and fable[1m] silently fall back to the standard 200k window with no error or warning.

Environment

• Claude Code version: 2.1.201 (confirmed up to date via claude update)
• OS: macOS 26.5.1 (BuildVersion 25F80)
• Plan: Enterprise / Claude for Work
• ~/.claude/settings.json has "model": "sonnet[1m]" explicitly pinned — same result as using /model sonnet[1m] interactively
• No ANTHROPIC_MODEL / CLAUDE_CODE_MODEL env vars set that could override the alias

Additional notes

• This does not appear to be a plan/entitlement gate — the platform docs state 1M context is generally available (GA, no surcharge) and enterprise plans have no separate toggle to enable it.
• Possibly related to prior reports of the Sonnet 1M status-bar/context mismatch, e.g. #61734 and #26428, though those predate the current Sonnet 5 / Fable 5 models and were closed as not planned — this report is specifically about the [1m] alias not taking effect (not just a status-bar display issue) for non-Opus models on the current CLI version.