How to use Anthropic Claude Opus 4.5 for Free in OpenCode using Antigravity
OpenCode is an open source alternative to Claude Code which everyone seem to like recently it has tons of features like web support, using other AI APIs (bring your own keys), etc
And on the other side, we’ve Google Antigravity IDE which gives us generious access to models like Claude Opus 4.5, Claude Sonnet 4.5, Gemini 3 Pro, etc.
Thanks to community OpenCode plugin for Antigravity, we can use the LLM that is available in Antigravity for free.
How to get started?
All you need to do is configure include that plugin in opencode config:
~/.config/opencode/opencode.json
And include
{
"$schema": "https://opencode.ai/config.json",
"plugin": ["opencode-antigravity-auth@beta"],
"provider": {
"google": {
"models": {
"antigravity-gemini-3-pro": {
"name": "Gemini 3 Pro (Antigravity)",
"limit": { "context": 1048576, "output": 65535 },
"modalities": { "input": ["text", "image", "pdf"], "output": ["text"] },
"variants": {
"low": { "thinkingLevel": "low" },
"high": { "thinkingLevel": "high" }
}
},
"antigravity-gemini-3-flash": {
"name": "Gemini 3 Flash (Antigravity)",
"limit": { "context": 1048576, "output": 65536 },
"modalities": { "input": ["text", "image", "pdf"], "output": ["text"] },
"variants": {
"minimal": { "thinkingLevel": "minimal" },
"low": { "thinkingLevel": "low" },
"medium": { "thinkingLevel": "medium" },
"high": { "thinkingLevel": "high" }
}
},
"antigravity-claude-sonnet-4-5": {
"name": "Claude Sonnet 4.5 (Antigravity)",
"limit": { "context": 200000, "output": 64000 },
"modalities": { "input": ["text", "image", "pdf"], "output": ["text"] }
},
"antigravity-claude-sonnet-4-5-thinking": {
"name": "Claude Sonnet 4.5 Thinking (Antigravity)",
"limit": { "context": 200000, "output": 64000 },
"modalities": { "input": ["text", "image", "pdf"], "output": ["text"] },
"variants": {
"low": { "thinkingConfig": { "thinkingBudget": 8192 } },
"max": { "thinkingConfig": { "thinkingBudget": 32768 } }
}
},
"antigravity-claude-opus-4-5-thinking": {
"name": "Claude Opus 4.5 Thinking (Antigravity)",
"limit": { "context": 200000, "output": 64000 },
"modalities": { "input": ["text", "image", "pdf"], "output": ["text"] },
"variants": {
"low": { "thinkingConfig": { "thinkingBudget": 8192 } },
"max": { "thinkingConfig": { "thinkingBudget": 32768 } }
}
},
"gemini-2.5-flash": {
"name": "Gemini 2.5 Flash (Gemini CLI)",
"limit": { "context": 1048576, "output": 65536 },
"modalities": { "input": ["text", "image", "pdf"], "output": ["text"] }
},
"gemini-2.5-pro": {
"name": "Gemini 2.5 Pro (Gemini CLI)",
"limit": { "context": 1048576, "output": 65536 },
"modalities": { "input": ["text", "image", "pdf"], "output": ["text"] }
},
"gemini-3-flash-preview": {
"name": "Gemini 3 Flash Preview (Gemini CLI)",
"limit": { "context": 1048576, "output": 65536 },
"modalities": { "input": ["text", "image", "pdf"], "output": ["text"] }
},
"gemini-3-pro-preview": {
"name": "Gemini 3 Pro Preview (Gemini CLI)",
"limit": { "context": 1048576, "output": 65535 },
"modalities": { "input": ["text", "image", "pdf"], "output": ["text"] }
}
}
}
}
}
Once you’ve inlcuded it, now authenticate using the Google
opencode auth login
That’s pretty much it, now you should be able to use those models in OpenCode.
Just make sure you’re on latest version of OpenCode if you face any issue.
Reference
