Google Tests Internal Gemini 4 'Carbon' Model on Coding Platform Jetski

Google has not released a Gemini 4 model named Carbon, but internal testing of a checkpoint with that codename is in progress on the company's internal coding platform, Jetski, Business Insider reported on October 9, 2026. The testing is limited to Google engineers and has not been accompanied by a public model ID, benchmark results, pricing information, or an official announcement.

One unnamed employee said the Carbon checkpoint "feels like Opus 5.5" in coding tasks, while also noting that further testing is required. The comment reflects a subjective impression rather than a quantified performance metric.

The Gemini 4 Argon version, which reached general availability on October 13, 2026, remains the only publicly accessible model in the Gemini 4 line. Argon is available through the Gemini API, Google AI Studio, and Google Cloud, and its performance has shown mixed results across different benchmarks.

Industry analysts note that internal testing on platforms like Jetski is common practice, allowing engineers to evaluate pre-release models on real coding work before a public launch. However, the existence of a checkpoint does not guarantee that a model will be released, nor that it will retain the same codename.

Developers are advised to continue using the available Argon model and to monitor official Google communications for any updates regarding new Gemini 4 checkpoints or releases.