Google Antigravity Adds Claude Opus 5.5 and Sonnet 5.5 for Paid Subscribers

What Happened

Antigravity is Google's autonomous coding workspace: it plans, writes and tests code across complex software repositories. The new additions are the thinking variants of Claude Sonnet 5.5 and Claude Opus 5.5. According to outlets that checked the documentation, only paid Google AI Pro and Google AI Ultra subscribers get them — Free, Plus and Enterprise accounts are excluded, and trial Pro subscriptions don't qualify.

The same documentation published a retirement schedule: Claude Sonnet 4.6, Claude Opus 4.6 and GPT-OSS-120B leave Antigravity on November 2, 2026. The docs say the reasoning-model choice persists within a conversation, and switching models while an agent is running won't affect the active turn.

Key Facts

1. New models: Claude Opus 5.5 / Claude Sonnet 5.5 (thinking), listed in Antigravity's official model documentation on Oct 3.
2. Who gets them: Google AI Pro and AI Ultra paid subscribers only; Free, Plus, Enterprise and trial Pro accounts are excluded.
3. Retiring: Claude Sonnet 4.6, Claude Opus 4.6 and GPT-OSS-120B leave on November 2, 2026.
4. Division of labor: Sonnet 5.5 targets faster, cheaper task execution; Opus 5.5 targets deep reasoning and long-horizon agent workflows (per PC-Tablet).

Context

Google is one of Anthropic's early investors. Putting a rival's newest flagships inside Google's own flagship developer tool, alongside Gemini, is a first. This site reported Anthropic's Sonnet 5.5 launch on Sept 28: output runs 30%+ faster than Sonnet 5 at unchanged API prices, typically needing fewer tokens for the same work.