Gemini 4 Carbon vs Opus 5.5: 59 vs 58, but only one is open

Gemini 4 Carbon vs Opus 5.5 is a comparison between a model you can use and one you mostly can't. Google announced Gemini 4 Carbon on October 28, 2026, but access is limited to a subset of cyber defenders. Claude Opus 5.5, released by Anthropic on September 22, is on sale to everyone.

On Artificial Analysis's Intelligence Index, Carbon scores 59 and Opus 5.5 scores 58. That is a one-point gap between models with different settings, and only one of them is open to developers today.

This comparison is based on the products' docs and published results, read on October 29, 2026. We did not run either model.

Gemini 4 Carbon vs Opus 5.5 at a glance

Sources: Google's Carbon announcement, Anthropic's Opus 5.5 announcement and the Claude pricing page, read on October 29, 2026. Prices change, so check the pages before you commit.

Is Gemini 4 Carbon available?

Not to most people. Google says access started the week of October 28 for a subset of cyber defenders, and that it will widen to other trusted partners through the Fairwind Program. It gives no date for developers, businesses or consumers. Our article on whether Gemini 4 Carbon is available tracks what Google has said.

Opus 5.5 has no such gate for general use. Anthropic does restrict some uses: biology research needs its Life Sciences Verification Program, and it says it is expanding its Cyber Verification Program to include Opus 5.5. Flagged cybersecurity tasks are rerouted to Opus 4.8.

Price: the introductory rate has no end date

Google lists Carbon at $2 per million input tokens and $10 per million output tokens as an introductory price, and $4 and $20 afterward. It does not say when the introductory price ends. Opus 5.5 costs $4 and $20 now. Anthropic says that is about 40% less than Opus 5 on typical workloads at default settings.

Since Carbon is not on sale to the public, the listed price is a plan, not something you can buy today. Opus 5.5 also has a fast mode, up to 2.5 times faster, at $8 input and $40 output per million tokens. Google describes no equivalent for Carbon.

Benchmarks: independent and company-reported

Independent: Artificial Analysis ranks Carbon first on its Intelligence Index v5.0 at 59. Opus 5.5 scores 58 at Max effort and 57 at Xhigh. Artificial Analysis's page did not show a price or context window for either model when we read it. The two models were tested at different effort settings, so treat the gap as close to a tie.

Reported by Google for Carbon:

• SEC-bench Pro, which tests finding vulnerabilities: 88.2%
• ExploitGym, which tests exploitation: 54.8%
• CWE-bench, which tests patching: 71.0%
• WebDev Arena: 1768 Elo, up 89 points, ranked fourth

Reported by Anthropic for Opus 5.5, mostly at max effort: Terminal-Bench 4.0 at 66.4%, CursorBench 4.0 at 57.8%, FrontierCode v1.1 at 54.4%, and Humanity's Last Exam with tools at 67.7%. Anthropic also reports an OSWorld 2.1 score of 81.8%.

The two companies picked different benchmarks, so none of these numbers can be set against each other. Carbon's list leans toward security. Opus 5.5's leans toward coding agents and knowledge work. Both are company claims until someone else runs them.

What each model is for

Google pitches Carbon at cybersecurity and long-horizon agent work, saying internal teams saw it run for days. Anthropic pitches Opus 5.5 at long-running coding and knowledge work, with adaptive thinking that cannot be turned off.

If you need a model today, the choice is made for you: Opus 5.5, or Google's Gemini 4 Argon, which Carbon beats 59 to 50 on the same index. If you are a security team, ask Google about Fairwind access.

What we don't know yet

Carbon's context window, output limit, rate limits and public release date are not published. Neither is its availability on any cloud platform. Watch for Google adding Carbon to its Gemini API pricing page, which would be the first sign it can be called without an invitation.