Gemini 4 Carbon Explained: What Google Is Testing

Illustration of Google's internal Gemini 4 Carbon AI model checkpoint being tested in a glass chamber, 2026

An internal Gemini 4 checkpoint called Carbon is being tested by Google staff — and one engineer’s ‘feels like Opus 5.5’ verdict is the most talked-about unreleased-model claim of the week. We separate what’s confirmed from what’s hype.