Gemini 4 Carbon edges out Claude Opus 5.5 on AI index

A one-point lead in intelligence

The latest head-to-head matchup between Google and Anthropic reveals a very tight race at the frontier of AI capabilities. According to a report by shattered.io, Gemini 4 Carbon scored 59 on the Artificial Analysis Intelligence Index v5. This puts it just one point ahead of Anthropic's Claude Opus 5.5, which received a score of 58.

The Intelligence Index evaluates models across nine different tests divided into four categories. These include knowledge work, coding, science, and general capability. While the one-point gap is the headline, analysts suggest it may be within the margin of error for a first run of this specific index version.

The results show that Google's new model excels in specific areas like the HLE-Diamond and Terminal-Bench-Science tests. However, the competition remains incredibly close, with OpenAI's GPT-6 Astra sitting just two points behind these leaders at 57. This indicates that the gap between the top three models is narrowing significantly.

Coding vs. Long-context reasoning

Despite the slight lead in the overall index, the two models show distinct strengths depending on the user's specific needs. Claude Opus 5.5 continues to be the preferred choice for software development and coding agents. It scored 62 on the Coding Agent Index, beating Carbon's score of 59.

In contrast, Gemini 4 Carbon demonstrates significant advantages in handling large amounts of data and complex security tasks. It leads by approximately 30 points in long-input reasoning and shows a 20-point advantage in exploitation work. These capabilities make it particularly suited for auditing massive codebases or analyzing lengthy legal documents.

Users must weigh these trade-offs based on their daily workflows. If a team is primarily building pull requests and office documents, Opus 5.5 is the current winner. If a user is performing deep security research or needs to process a 900-page contract set, Carbon is the more capable tool.

Access and availability hurdles

A major distinction between the two models is who can actually use them right now. Anthropic has made Opus 5.5 widely available through its API and major cloud providers like Amazon Web Services and Microsoft Azure. This makes it the practical choice for most businesses looking to integrate high-end AI today.

Google's situation is more complicated because Carbon is currently restricted. While it was announced on October 28, 2026, it is only available to selected cyber defenders and trusted partners through the Fairwind Program. This means most general users cannot yet access the model that technically holds the highest index score.

For those who cannot access Carbon, Google offers Gemini 4 Argon as the generally available flagship. Argon reached developers on October 13 and serves as the current production model for the Gemini app. While Carbon is the announced successor, Argon remains the primary option for standard enterprise and consumer use.

Cost efficiency and performance

Pricing dynamics also vary significantly when looking at the actual cost per completed task. A benchmark by SemiAnalysis showed that Carbon costs roughly $16.29 per task on the GDPx test. This is considerably cheaper than the $51.41 required to complete a similar task using Claude Opus 5.5.

These price differences are largely driven by how many tokens each model consumes during a job. Because Carbon is more efficient in certain automated workflows, it provides a better performance-per-dollar ratio for specific tasks. However, Anthropic notes that Opus 5.5 can be tuned to run at medium effort to help users manage costs.

Standard sticker prices for both models are set at $4 per million input tokens and $20 per million output tokens starting in late 2026. Despite these similar base prices, the underlying architecture and caching economics mean that the final bill for a user will depend heavily on the complexity of the prompts provided.

Safety and hallucination rates

The two labs also report different results regarding how often their models make mistakes or succumb to manipulation. On the AA-Omniscience test, which rewards accuracy, Carbon scored 54 compared to 48 for Opus 5.5. However, the hallucination rate tells a different story, with Carbon guessing more often when it lacks information.

Google claims that Carbon reached a 0.0% success rate against all evaluated attacks on the Gray Swan benchmark. Anthropic similarly claims that Opus 5.5 ties for the lowest prompt injection success rate of any model tested on that same platform. Because these tests were run independently, the results are not directly comparable.

Both companies are also focusing on reward hacking, which is when an AI finds a way to