A screenshot posted by @bidyut_io shows a Gemini model string, gemini-4-carbon-preview, highlighted in what looks like a list of model identifiers, directly below gemini-4-flash-preview. Google's Gemini API documentation lists only one Gemini 4 model, Gemini 4 Argon (gemini-4-argon), and neither Carbon nor a Gemini 4 Flash appears there. Google has not announced either name.

The technical receipt

The cropped image shows four lines, each ending in a colon, as in a config or JSON-style mapping:

  • "gemini-3.5-flash-lite":

  • "gemini-3.8-flash":

  • "gemini-4-flash-preview":

  • "gemini-4-carbon-preview": (highlighted in blue)

Cropped list of Gemini model strings with gemini-4-carbon-preview highlighted below gemini-4-flash-preview
Cropped list of Gemini model strings with gemini-4-carbon-preview highlighted below gemini-4-flash-preview

Image credit: @bidyut_io on X

The post names only Carbon, but the line directly above it is a second string, gemini-4-flash-preview.

The two older strings are shipped models. Google's models page lists "Gemini 3.8 Flash | gemini-3.8-flash" and "Gemini 3.5 Flash-Lite | gemini-3.5-flash-lite". The screenshot's list therefore mixes shipped identifiers with unlisted ones, and the image does not show which system the list comes from.

What Google's pages list

Google's models page shows a single Gemini 4 entry: "Gemini 4 Argon | gemini-4-argon", described as a flagship reasoning model "with a unified 1M context window and long decodes up to 1M tokens". The release notes record its general availability on October 13, 2026, and contain no entry for Carbon. For context, Argon's pricing page lists standard input at "$2.00 through November 30, 2026. $4.00 starting December 1, 2026" and output at "$10.00 through November 30, 2026. $20.00 starting December 1, 2026" per 1M tokens. Nothing is published for Carbon, so there is no like-for-like comparison to make. We have covered Argon's announcement and its ARC-AGI-3 results.

The poster's added claims

@bidyut_io calls the string "the latest internal Gemini 4 checkpoint", says a report shows it at Opus 5.5 level on coding tasks, and adds that "Argon was Barium-B. Carbon is next." The post shows no report, benchmark or link behind the coding claim, and Google's pages do not confirm the codename history or the "next" framing. Our read: the screenshot shows the string exists somewhere, which fits a model in testing, but it does not show what Carbon is, how it relates to Argon, or who can call it.

Sources