OpenAI's GPT-5.5 is here, and it's no potato: narrowly beats Anthropic's Claude Mythos Preview on Terminal-Bench 2.0

After months of rumors and reports that OpenAI was developing a new, more powerful AI large language model for use in ChatGPT and through its application programming interface (API), allegedly codenamed "Spud" internally, the company has today unveiled its latest offering under the more formal name GPT-5.5.

And to likely no one's surprise, it's hardly a "potato" in the disparaging sense of the word: GPT-5.5 retakes the lead for OpenAI in generally available LLMs, coming ahead of rivals Anthropic's and Google's latest public offerings, and even beating the private Anthropic Claude Mythos Preview model narrowly on one benchmark (essentially a statistical tie).

"It’s definitely our strongest model yet on coding, both measured by benchmarks and based on the feedback that we’ve gotten from trusted partners, as well as our own experience," explained Amelia "Mia" Glaese, VP of Research at OpenAI, in a video call with journalists ahead of the launch earlier today.

OpenAI positions GPT-5.5 as a fundamental redesign of how intelligence interacts with a computer's operating system and professional software stacks.

"What is really special about this model is how much more it can do with less guidance," said OpenAI co-founder and president Greg Brockman on the same call. "It’s way more intuitive to use. It can look at an unclear problem and figure out what needs to happen next."

Brockman proceeded to emphasize the areas in which users can expect to see gains from using GPT-5.5 compared to OpenAI's prior state-of-the-art model, GPT-5.4, which remains available (for now) to users and enterprises at half the API cost of its new successor.

"It’s extremely good at coding," Brockman said of GPT-5.5. "It’s also great at broader computer work, computer use, scientific research—these kinds of applications that are very intelligent bottlenecks."

OpenAI CEO and-cofounder Sam Altman also weighed in on the launch and the company's philosophy in a post on X, writing, in part: "We want our users to have access to the best technology and for everyone to have equal opportunity."

The model is available in two variants: GPT-5.5 and GPT-5.5 Pro, distinguished by the latter offering enhanced precision and specialized logic for handling the most rigorous cognitive demands.

While the standard version serves as the versatile flagship for general intelligence tasks, the Pro model is architected specifically for high-stakes environments such as legal research, data science, and advanced business analytics where accuracy is paramount. This premium tier provides noticeably more comprehensive and better-structured responses, supported by specialized latency optimizations that ensure high-quality performance during complex, multi-step workflows.

Unfortunately for third-party software developers, API access is not yet available for either GPT-5.5 nor GPT-5.5 Pro and will be coming "very soon," according to the company's announcement blog post.

"API deployments require different safeguards and we are working closely with partners and customers on the safety and security requirements for serving it at scale," OpenAI writes.

For the time being, GPT-5.5 is available only to paying subscribers of the ChatGPT Plus ($20 monthly), Pro ($100-$200 monthly), Business, and Enterprise users, with GPT-5.5 Pro access starting at the Pro tier and upwards.

A focus on agency

At the core of GPT-5.5 is a focus on "agentic" performance—specifically in coding, computer use, and scientific research.

Unlike its predecessors, which often required granular, step-by-step prompting to avoid "hallucinating" a path forward, GPT-5.5 is designed to handle messy, multi-part tasks autonomously.

It excels at researching online, debugging complex codebases, and moving between documents and spreadsheets without human intervention.

One of the most significant technical leaps is the model's efficiency. While larger models typically suffer from increased latency, GPT-5.5 matches the per-token latency of the previous GPT-5.4 while delivering a higher level of intelligence.

This was achieved through a deep hardware-software co-design. OpenAI served GPT-5.5 on NVIDIA GB200 and GB300 NVL72 systems, utilizing custom heuristic algorithms—written by the AI itself—to partition and balance work across GPU cores.

This optimization reportedly increased token generation speeds by over 20%. For high-stakes reasoning, the "GPT-5.5 Thinking" mode in ChatGPT provides smarter, more concise answers by allowing the model more internal "compute time" to verify its own assumptions before responding.

This capability is particularly visible in the model’s performance on "Expert-SWE," an internal OpenAI benchmark for long-horizon coding tasks with a median human completion time of 20 hours. GPT-5.5 notably outperformed GPT-5.4 on this metric while using significantly fewer tokens.

Benchmarks show OpenAI has retaken the lead

The market for leading U.S.-made frontier models has become an increasingly tight race between OpenAI, Anthropic, and Google.

Literally a week ago to the date, OpenAI rival Anthropic released Opus 4.7, its most powerful generally available model, to the public, taking over the leaderboard in terms of the number of third-party benchmark tests in which it has the lead.

Yet today, GPT-5.5 has surpassed it and even Anthropic's heavily restricted, more powerful model Claude Mythos Preview, albeit only on one benchmark, Terminal-Bench 2.0, which tests "a model's ability to navigate and complete tasks in a sandboxed terminal environment."

GPT-5.5 achieved 82.7% accuracy on Terminal-Bench 2.0, easily surpassing Opus 4.7 (69.4%) and narrowly beating the Mythos Preview (82.0%).

However, in multidisciplinary reasoning without tools, the landscape is more competitive. On Humanity's Last Exam without tools, GPT-5.5 Pro scored 43.1%, trailing behind Opus 4.7 (46.9%) and Mythos Preview (56.8%).

This suggests that while OpenAI is winning on "computer use" and "agency," other models may still hold an edge in pure, zero-shot academic knowledge.