Claude Opus 5.5 and Claude Sonnet 5.5 are now available in Google Antigravity

Claude Opus 5.5 and Claude Sonnet 5.5 available in Antigravity | Google Cloud Blog

AI & Machine Learning

Claude Opus 5.5 and Claude Sonnet 5.5 are now available in Google Antigravity

October 21, 2026

##### Marialaura Garcia

Product Marketing Manager, Google Cloud

##### Rich Hyndman

Developer Relations, Google Antigravity

Whether you are iterating on a quick bug fix or planning a complex migration, different tasks call for different models.

In keeping with Google Cloud's commitment to an open ecosystem and to give developers the right model for every job, Claude Opus 5.5 and Claude Sonnet 5.5 are now available in Google Antigravity for Google Cloud customers. Claude Opus 5.5 is built for complex work while Claude Sonnet 5.5 is a faster, lower-cost complement.

Once enabled by an administrator, developers can select Claude Opus 5.5 and Sonnet 5.5 directly from the model picker. Administrators can also select Google’s Gemini models, including Gemini 3.8 Flash and Gemini 4 Argon. The models apply across Antigravity 2.0, Antigravity CLI and our recently released Antigravity IDE extensions for VS Code, JetBrains IntelliJ, and Visual Studio. This lets you choose the right model for the job, under a unified enterprise billing and security boundary.

In this post, we’ll share two engineering patterns for building in Antigravity using these models. To view the entire list of models supported in Antigravity across subscriptions, see our documentation here .

Multi-model engineering patterns in Antigravity

Having multiple model families available inside the same agent harness unlocks practical multi-model workflows that improve code quality while controlling latency and cost.

Pattern 1: Cross-model verification ("LLM-as-a-Judge") in loop and graph workflows

When building agentic loops or multi-step graph workflows, using the same model to both write code and review its own output can reinforce model-specific blind spots. Pairing two distinct model families, one as the implementer and another as the validator (judge), provides independent verification before moving to the next stage of a workflow.

In Antigravity, you can run this pattern either interactively or via automated subagents:

• Plan and implement with Model A: Start in planning mode using Claude Opus 5.5 or Gemini 4 Argon to design and implement a multi-file change.

• Validate with Model B: Before committing or advancing the loop, switch models, or invoke a one-shot /model check in the CLI, to have a different model family critique the implementation against your test suite and requirements.

Pattern 2: Pairing reasoning models with Flash subagents

Complex engineering tasks often combine a few high-reasoning decisions with dozens of high-volume, mechanical lookups (searching files, grepping logs, checking lint output, or classifying test failures). Running every lookup on a frontier model can increase both latency and spend.

Antigravity's Subagent customization system ( .agents/agents/*.md ) lets you assign specific model tiers ( inherit , flash , or pro ) to specialized subagents. When your primary session is running a more powerful model.

Subagents configured with model: inherit use your active session model for deep reasoning subtasks.

Subagents configured with model: flash offload high-speed search, classification, and triage work to Gemini Flash models.

For example, you can define a fast log-triage subagent in .agents/agents/test-triager.md :

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--- name: test-triager description: Runs unit tests, classifies failures, and returns a concise summary of failing assertions. model: flash tools: - read - edit --- Run the requested test targets, classify any failures by root cause (compilation error, assertion failure, or timeout), and return a structured summary to the parent agent.

And a cross-model code reviewer subagent in .agents/agents/gemini-judge.md :

--- name:cross-model-judge description: Independent LLM-as-a-judge verifier that audits diffs and edge cases using Gemini Pro. model: pro tools: - read --- Review the current workspace diff against the user's requirements. Check for regressions, missing edge-case tests, and security issues. Output a pass/fail verdict with specific line references.

With this setup, you can delegate rapid test-and-classify loops to test-triager and trigger cross-model-judge to validate the final diff, combining the strengths of each model in a single workflow.

Getting started

Claude Opus 5.5 and Claude Sonnet 5.5 are available now for Google Cloud customers using Antigravity:

• Administrators (Gemini for business): Third-party partner models do not draw from the pooled Gemini Enterprise Standard and Plus edition monthly token quota. Instead, usage is billed on a pay-as-you-go basis through your existing Google Cloud Billing account, so overages must be enabled. Visit “Gemini Enterprise” > “Settings” > “AI developer tools” in the Google Cloud Console to configure overage billing, spend limits and authorize partner models for your organization. See Configure AI developer tools settings for step-by-step instructions.

• Administrators (Gemini platform): You can also enable partner models if you are using Antigravity through the API in Gemini platform. Enable Claude models in Model Garden and complete the standard Anthropic terms.

• Developers: Update to the latest version of Antigravity 2.0, the Antigravity CLI, or the Antigravity IDE extensions, and open the model picker (or run /model ) to select the right model for your task. To learn more about enterprise governance and multi-agent configuration, visit the Google Antigravity Enterprise documentation . You can switch the active model between turns in the same conversation thread while preserving workspace state, open artifacts, and terminal context.

Note: Lightweight first-party Gemini models continue to run in the background to handle high-frequency client-side coordination, such as context management and summaries. They consume first-party tokens and can incur charges.

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