[BUG] Skill `model:` frontmatter triggers 429 "Extra usage required" on 2.1.76 when session uses opus[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?

On Claude Code 2.1.76, invoking any skill with model: sonnet in frontmatter from an opus[1m] (1M context) session immediately fails with:

API Error: Rate limit reached

This happens on a fresh session with zero prior API calls. It does not happen on 2.1.75.

What Should Happen?

When opus[1m] is used, the skill using sonnet (sonnet[1m] more specifically) should be invoked without any issue.

Error Messages/Logs

Run `claude --debug`, invoke the skill, check `~/.claude/debug/*.txt`:


[ERROR] API error (attempt 1/11): 429 429 {
  "type": "error",
  "error": {
    "type": "rate_limit_error",
    "message": "Extra usage is required for long context requests."
  }
}


The error is not a rate limit — it's an access restriction. The API rejects `sonnet[1m]` because the account doesn't have "extra usage" enabled for sonnet long-context.

Steps to Reproduce

1. Claude Code 2.1.76, Max plan, opus[1m] as session model (default)
2. Create a skill:

---
name: test-sonnet
description: Test sonnet model switch
model: sonnet
user-invocable: true
---
Say hello.

1. Invoke /test-sonnet → immediate 429

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.75

Claude Code Version

2.1.76

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

Root cause: Pl6 (SkillModelOverride) in 2.1.76

The 2.1.76 changelog states: "Fixed spurious 'Context limit reached' when invoking a skill with model: frontmatter on a 1M-context session."

This was fixed by adding Pl6, which auto-promotes skill models to [1m] when the session is on a 1M model.

File: cli.js (minified single-file bundle)

| Function | Offset | Purpose |
|----------|--------|---------|
| Pl6 | 10717414 | SkillModelOverride — appends [1m] to skill model |
| Cf | 10718894 | Checks if a model string contains [1m] (/\[1m\]/i.test(A)) |
| gr8 | 10718950 | Checks if model supports 1M context (true for sonnet-4, opus-4-6) |
| Pn8 | 10719150 | Auto-enables 1M for plain sonnet when coral_reef_sonnet flag is set |
| HLA | 1023779 | Reads coral_reef_sonnet from server-side clientDataCache |
| contextModifier | 8358160 | Where Pl6 wraps the skill model assignment in the Skill tool |

// contextModifier in Skill tool (offset ~8358160)

// 2.1.75 — direct assignment, no promotion
if(D) N={...N, options:{...N.options, mainLoopModel:D}};

// 2.1.76 — wrapped with Pl6 auto-promotion
if(D) V={...V, options:{...V.options, mainLoopModel:Pl6(D, N.options.mainLoopModel)}};

Pl6 (offset 10717414):

function Pl6(A, q) {
  if (Cf(A) || !Cf(q)) return A;      // skip if skill model already has [1m] OR session model doesn't have [1m]
  if (gr8(H5(A))) return A + "[1m]";   // promote if model supports 1m
  return A;
}

When session is opus[1m] and skill has model: sonnet:

• Cf("sonnet") → false (no [1m] suffix)
• Cf("opus[1m]") → true (session has [1m])
• gr8("sonnet") → true (sonnet supports 1m)
• Result: "sonnet" + "[1m]" → "sonnet[1m]"

The API receives sonnet[1m] and rejects it with 429.

The gap

The 1M context GA announcement states: "Claude Opus 4.6 and Sonnet 4.6 now include the full 1M context window at standard pricing." But for Claude Code, sonnet[1m] is gated behind the coral_reef_sonnet feature flag and requires "extra usage" billing — contradicting the announcement that it's included at standard pricing.

Either sonnet[1m] should be made available to Max plan users to match the announcement, or Pl6 should check account entitlement (HLA()) before promoting sonnet to sonnet[1m].

Version comparison

| Version | Skill contextModifier | Behavior |
|---------|----------------------|----------|
| 2.1.70–2.1.75 | mainLoopModel:D | Skill runs as plain sonnet (200K). Auto-compaction if >200K. |
| 2.1.76 | mainLoopModel:Pl6(D,...) | Sonnet promoted to sonnet[1m]. Rejected if account lacks entitlement. |

Workarounds

• Stay on 2.1.75 — skill model switching works correctly without auto-promotion. Caveat: if a sonnet skill (200K) is invoked from an opus[1m] session with >200K context, auto-compaction fires or "Context limit reached" occurs (the original bug that 2.1.76 tried to fix).
• Use opus for all skills — remove model: sonnet from skill frontmatter so everything runs on the session model. Trades speed/cost for reliability.