Claude Opus 4.6 is no longer available. Please switch to Claude Opus 5.5

Google Antigravity
1

After using up my OPUS 5.5 quota on my main Pro account, I switched to a free account to use OPUS 4.6.
I got the message: “Claude Opus 4.6 is no longer available. Please switch to Claude Opus 5.5.”
Does anyone know how to fix this?

2

Hi @Randy3,

Thanks for reaching out! That message happens because your window or active chat thread is still holding onto cached model routing from your Pro account after you switched to your Free account.

Per Choose a model | Google Antigravity Docs, Claude Opus 5.5 (thinking) is only for paid Pro/Ultra plans, while Claude Opus 4.6 (thinking) is still available on Free accounts until November 2, 2026.

To fix this on your Free account:

  1. Open the Command Palette (Ctrl+Shift+P / Cmd+Shift+P) and run Antigravity: Reset Onboarding to clear the cached Pro session and sign in cleanly with your Free account.
  2. Start a New Chat (Ctrl+N / Cmd+N) rather than continuing the Opus 5.5 thread, then select Claude Opus 4.6 (thinking), Claude Sonnet 4.6 (thinking), or Gemini 3.8 Flash.

Also, if you want to stay on your main Pro account without waiting for the 5-hour quota refresh (Plans | Google Antigravity Docs), you can switch to Claude Sonnet 5.5 (thinking) or Gemini 3.8 Flash, or turn on AI Credit Overages → Always in Settings (Plans | Google Antigravity Docs).