Opus 4.6 Now Defaults to Medium Effort with Ultrathink Restored

Opus 4.6 Gets Smarter Defaults in Claude Code

Claude Code v2.1.68, published on March 4, 2026, tightens the reasoning configuration around Opus 4.6 with three tightly related changes that together define how the model thinks out of the box and on demand.

Medium Effort: The New Default for Max and Team

For Max and Team plan subscribers, Opus 4.6 now launches in medium effort mode rather than the previous default. Anthropic describes medium effort as the sweet spot between throughput and reasoning depth — thorough enough for the majority of coding workflows, but faster and cheaper than high effort. The active effort level is now also displayed in the logo and spinner area (e.g., "thinking with medium effort"), making it immediately visible without requiring a /model inspection.

Ultrathink Returns

The "ultrathink" keyword, which instructs Claude Code to apply maximum reasoning intensity for the current turn, has been re-introduced after a brief absence. Typing ultrathink in a prompt triggers high-effort reasoning for that single turn only, leaving the global default unchanged. This gives developers a lightweight override for unusually complex tasks — algorithmic design sessions, deep debugging, or large refactors — without permanently escalating the effort level and its associated cost.

Legacy Opus Versions Retired

Opus 4 and Opus 4.1 have been removed from the Claude Code first-party API. Users who had those model IDs pinned in their configuration are automatically migrated to Opus 4.6 with no additional action required. This consolidation simplifies the model landscape for Opus-class reasoning in Claude Code, leaving Opus 4.6 as the single Opus option.