[BUG] Pattern of undisclosed 1M context billing changes affecting Max plan users — cross-issue summary

Summary

This issue documents a systemic pattern across multiple open reports where Max plan subscribers are being charged extra usage — or denied access entirely — for 1M context that is documented as included with their subscription. This is not an isolated bug; it is a recurring, multi-version billing problem.

Affected Issues (all open)

| Issue | Description |
|-------|-------------|
| #28927 | Silent billing change in v2.1.51 — JSONL data proves identical workload billed differently post-update |
| #34773 | Sonnet 4.6 1M missing from /model picker entirely on Max 20x |
| #39841 | Opus 1M blocked unless extra usage enabled; tengu_hawthorn_window stays at 200K regardless |
| #43276 | Max plan hitting 429 'Extra usage required' at only 17K tokens |

Root Cause (identified in #39841)

The GrowthBook feature flag tengu_hawthorn_window is not being correctly flipped from 200000 to 1000000 for Max plan users. The context window never actually changes server-side even when the model picker accepts the 1M model — meaning users are either blocked, incorrectly billed, or silently given 200K despite selecting 1M.

My Environment

• Plan: Claude Max
• Claude Code: v2.1.133 (latest as of May 7, 2026)
• OS: macOS
• Observed: Sonnet 4.6 has no 1M option in /model; Opus 4.6 1M shows but behavior is inconsistent with documented entitlements

What the docs say

From model-config docs:

On Max, Team, and Enterprise plans, Opus is automatically upgraded to 1M context with no additional configuration. Included with subscription.

Pattern of problems

1. v2.1.51: 1M context silently moved to extra-usage billing with no changelog entry (#28927)
2. v2.1.85+: /model opus[1m] blocked entirely when extra usage is disabled (#39841)
3. v2.1.133: Sonnet 4.6 1M missing from picker on Max 20x plan (#34773)
4. v2.1.91: 429 errors at minimal context usage on Max plan (#43276)

Requests

1. Fix tengu_hawthorn_window entitlement mapping for Max plan accounts
2. Ensure Sonnet 4.6 1M appears in /model for all Max plan tiers
3. Retroactively credit Extra Usage charges incurred due to the v2.1.51 silent billing change
4. Add explicit in-app notification before any billing behavior change
5. Align documentation with actual billing behavior — currently contradictory