How to Use Claude Opus in Antigravity for Free

If you're using Antigravity for agentic coding and automation, you probably already know how ridiculously powerful it is. But a lot of people don't realize you can actually hook it up to Claude Opus without necessarily paying massive API costs, provided you use the right setup.

Why Claude Opus?

Opus is currently one of Anthropic's most capable models, especially for deep reasoning, architectural planning, and complex coding tasks. Having it drive your Antigravity workflows means better code generation and fewer frustrating logic errors down the line.

The Setup Process

By default, Antigravity lets you pick from a variety of models out of the box. To get Opus running smoothly:

1. Accessing the Model Selection

Open up your Antigravity user settings or configuration dashboard. There's a dedicated dropdown for 'Model Selection'. This is where the magic happens. You'll want to swap from the default Gemini or GPT models over to the Anthropic suite.

2. API Keys and Workarounds

Usually, Opus requires a paid Anthropic API key. However, if you are participating in specific developer betas, hackathons, or using cloud provider credits (like AWS Bedrock or GCP Vertex AI which sometimes offer generous free startup tiers for Anthropic models), you can route those credentials straight into Antigravity.

Alternatively, some open-source router layers allow you to pool free tier limits, but honestly, the most reliable way is utilizing cloud provider startup credits. Grab your access token, drop it into the Antigravity config, and select the Opus variant.

Getting the Most out of It

Opus is a heavy model, so it can be slightly slower than Sonnet or Haiku. To keep your workflow snappy, use Opus specifically for architecture planning or debugging gnarly errors, and switch back to a faster model for simple boilerplate tasks. This maximizes efficiency while minimizing costs.