WebSearch and subagents fail with 'Extra usage required for 1M context' on Max plan

Description

When using Claude Code with Opus 4.6 (1M context) on the Max plan, both WebSearch tool and background subagents fail with the following error:

API Error: Extra usage is required for 1M context · run /extra-usage to enable, or /model to switch to standard context

Expected Behavior

Max plan should fully support 1M context features (WebSearch, subagent spawning) without requiring additional "extra usage" toggles.

Steps to Reproduce

1. Use Claude Code with Opus 4.6 (1M context) on the Max plan
2. Attempt to use WebSearch tool
3. Or spawn a background agent via the Agent tool

Both fail with the same error message.

Environment

• Model: Opus 4.6 (1M context) — claude-opus-4-6[1m]
• Plan: Max
• Platform: macOS (Darwin 25.4.0, Apple Silicon)
• Claude Code: CLI

Additional Context

The error message suggests running /extra-usage to enable or /model to switch to standard context. However, this seems unexpected for Max plan users who should have 1M context included.