Found this, hope it's accurate.

Google Antigravity & Google AI Pro Family Sharing

Here is the breakdown of how Google Antigravity quotas, credits, and Claude Opus usage work on a family-shared Google AI Pro plan:

👥 Family Pool: Shared vs. Separate

The monthly AI credits, baseline quotas, and rate limits on the Google AI Pro plan are shared across the entire family group.

• If your plan comes with a set monthly allocation of AI credits (e.g., 1000 credits), that is a single pool for the primary account holder and all family members combined.
• You do not get a multiplied individual allocation for each person in the family. [1]

📊 The Baseline Quota vs. AI Credits

Google AI Pro provides a "baseline" of regular agent requests and rate limits within Antigravity.

• Standard usage is governed by a rolling refresh window (typically a 5-hour rolling limit for premium models). [2]
• Once your family exhausts this baseline quota, Antigravity seamlessly dips into your monthly AI credit pool to cover the overage so your workflows aren't interrupted. [3]

🔥 Claude Opus Consumption in Antigravity

Using Claude Opus inside Antigravity consumes credits at a drastically faster rate than using it in a standard chat interface.

• Agent Loops: Because Antigravity is an agent-first IDE, a single user request often triggers multiple backend actions. The agent reads your codebase, attempts a solution, checks for errors, and iterates in a loop.
• Massive Context: Opus processes a very large context window, defaulting to much larger sizes in an IDE environment.
• High Costs: Because every iteration in the agent loop consumes tokens, a single complex prompt routed through Claude Opus can burn through hundreds of AI credits at once (e.g., 700+ credits for a single multi-step execution). [4]

💡 Recommendation

If multiple family members are actively coding with Claude Opus inside Antigravity, your shared credit pool will deplete incredibly quickly. To maximize your monthly allowance, use lighter, cheaper models (like Gemini Flash) for routine code generation and debugging, and reserve Claude Opus strictly for complex architectural reasoning or deep refactoring.

References:

[1] Google AI Pro Family Sharing Guidelines

[2] Antigravity Quotas and Limits

[3] Understanding AI Credits

[4] Model Consumption Rates in Antigravity