Google Staff Test New Gemini 4 'Carbon', Say It Feels Like Opus 5.5

Google employees are testing a new internal version of Gemini 4 codenamed Carbon, which one employee said “feels like Opus 5.5” for coding.

The model is a checkpoint following the upcoming public release of Argon and has been made available on Google’s internal coding platform, Jetski. Documents seen by Business Insider indicate Google has also tested a version named Barium.

Early versions of Argon were reportedly felt to be behind Claude Opus 5 on some coding tasks. Internal feedback suggests Carbon may close this gap, but Google has not guaranteed a public release.

These assessments are based on subjective employee impressions and unverified screenshots, not independent benchmarks; Google declined to comment.