GPT-5.5 matches Claude Mythos in cybersecurity capabilities as OpenAI plans controlled release

Amid Mythos' hyped cybersecurity prowess, researchers find GPT-5.5 is just as good

Last month, Anthropic made a big deal about the supposedly outsized cybersecurity threat represented by its Mythos Preview model, leading the company to restrict the initial release to "critical industry partners." But new research from the UK's AI Security Institute (AISI) suggests that OpenAI's GPT-5.5, which launched publicly last week, reached "a similar level of performance on our cyber evaluations" as Mythos Preview, which the group evaluated last month. Since 2023, the AISI has run a variety of frontier AI models through 95 different Capture the Flag challenges designed to test capabilities on cybersecurity tasks such as reverse engineering, web exploitation, and cryptography. On the highest-level "Expert" tasks, GPT-5.5 passed an average of 71.4 percent, slightly higher than the 68.6 percent achieved by Mythos Preview (though within the margin of error). In one particularly difficult task that involved building a disassembler to decode a Rust binary, AISI notes that "GPT-5.5 solved the challenge in 10 minutes and 22 seconds with no human assistance at a cost of $1.73" in API calls. GPT-5.5 also matched Mythos Preview in its progress on "The Last Ones" (TLO), an AISI test range set up to simulate a 32-step data extraction attack on a corporate network. GPT-5.5 succeeded in 3 of 10 attempts on TLO, compared to 2 of 10 for Mythos Preview -- no previous model had ever succeeded at the test even once. But GPT-5.5 still fails at AISI's more difficult "Cooling Tower" simulation of an attempted disruption of the control software for a power plant, as every previously tested AI model also has. Is it just "fear-based marketing"? The new results for GPT-5.5 suggest that, when it comes to cybersecurity risk, Mythos Preview was likely not "a breakthrough specific to one model" but rather "a byproduct of more general improvements in long-horizon autonomy, reasoning, and coding," AISI writes. In a recent interview with the Core Memory podcast, OpenAI CEO Sam Altman criticized what he calls "fear-based marketing" in promoting limited releases for certain AI models. While he said he's "sure Mythos is a great model for cybersecurity," he added that "it is clearly incredible marketing to say, 'We have built a bomb. We are about to drop it on your head. We will sell you a bomb shelter for $100 million.'" "There will be a lot more rhetoric about models that are too dangerous to release," Altman continued. "There will also be very dangerous models that will have to be released in different ways." In February, OpenAI rolled out its Trusted Access for Cyber pilot program, letting security researchers and enterprises verify their identities and register their interest in studying OpenAI's frontier models for "legitimate defensive work." Last month, OpenAI said it was using that trusted access list to control the limited launch of GPT-5.4-Cyber, a model variant that it says is "purposely fine-tuned for additional cyber capabilities and with fewer capability restrictions." On Thursday, OpenAI CEO Sam Altman said on social media that the initial release of GPT-5.5-Cyber would similarly be limited "to critical cyber defenders in the next few days."

OpenAI's new security model is for 'critical cyber defenders' only

It's not clear who will get access to the model first, though previous "trusted access" schemes involved vetted professionals and institutions. Details of the model and its capabilities are also unclear; OpenAI has not released any technical details or specifications. The name indicates it is a specialized version of the recently released GPT-5.5, which it called its "smartest and most intuitive to use model yet." The staggered rollout is part of a growing trend in the AI industry of companies branding their top models too dangerous for public release due to their potential for misuse. OpenAI has staggered the release of previous cybersecurity-focused models, in addition to its new purpose-built life sciences model GPT-Rosalind, which is intended to support biology research and drug discovery. This month, Anthropic followed a similar playbook with Claude Mythos, though with much greater fanfare, and it bungled the model's secure release in embarrassing ways.

OpenAI locks GPT-5.5-Cyber behind velvet rope

Altman's crew now doing the same gatekeeping it recently mocked OpenAI is lining up a limited release of its new GPT-5.5-Cyber model to a handpicked circle of "cyber defenders," just weeks after taking a swipe at Anthropic for doing almost exactly the same thing. CEO Sam Altman said in a post on X that the rollout will begin "in the next few days," with access restricted to a group he described as trusted defenders working to secure critical systems. "We will work with the entire ecosystem and the government to figure out trusted access for cyber," he wrote, adding that the goal is to "rapidly help secure companies and infrastructure." GPT-5.5-Cyber is built to spot flaws before anyone else abuses them. OpenAI says it can pentest, find bugs, exploit them, and tear apart malware, but as we have already seen, tools that break systems rarely stay in the right hands for long. OpenAI's announcement comes just weeks after Anthropic rolled out its own cyber-focused model, Claude Mythos, to roughly 50 organizations under tight controls, saying it would never be made publicly available - and Altman was not impressed. As reported by TechCrunch, he took aim at what he framed as exclusivity dressed up as caution during an appearance on the Core Memory podcast. "There are people in the world who, for a long time, have wanted to keep AI in the hands of a smaller group of people," he said. "You can justify that in a lot of different ways." He went further, likening the approach to selling fear. "We have built a bomb, we are about to drop it on your head. We will sell you a bomb shelter for $100 million." Now OpenAI is, if not building the same shelter, at least checking IDs at the door. Independent testing suggests the model is not just marketing fluff. The UK's AI Security Institute said this week that GPT-5.5-Cyber is "one of the strongest models we have tested on our cyber tasks," and noted it is only the second system to complete one of its multi-step attack simulations end to end. It may be pitched as protection, but when the tools can both break and fix systems, the difference often comes down to who gets there first. ®

OpenAI's GPT-5.5 Matches Claude Mythos in Cyberattack Capabilities: AI Security Institute - Decrypt

Researchers found a jailbreak that bypassed GPT-5.5's safety guardrails entirely, raising alarms. A U.K. government agency has found that OpenAI's newest artificial intelligence model can autonomously carry out complex cyberattacks -- and that it cracked a reverse-engineering challenge in just over 10 minutes that took a human security expert roughly 12 hours. The AI Security Institute (AISI), a research body within Britain's Department of Science, Innovation and Technology, published findings Thursday showing that GPT-5.5 is among the strongest models it has evaluated for offensive cyber capabilities, putting it roughly on par with Anthropic's vaunted Claude Mythos. The report found GPT-5.5 is the second model to complete AISI's most demanding test -- a 32-step simulated corporate network attack called "The Last Ones" -- doing so autonomously in two out of 10 attempts. The first model to achieve the milestone was Anthropic's Claude Mythos Preview, which completed the simulation in three of 10 tries. The corporate network simulation, built with the cybersecurity firm SpecterOps, requires an agent to chain together reconnaissance, credential theft, lateral movement across multiple Active Directory forests, a supply-chain pivot through a CI/CD pipeline, and ultimately the exfiltration of a protected internal database -- steps that AISI estimates would take a human expert around 20 hours. Perhaps the most striking result involved a fiendishly difficult reverse-engineering puzzle. GPT-5.5 solved the challenge -- which required reconstructing a custom virtual machine's instruction set, writing a disassembler from scratch, and recovering a cryptographic password through constraint solving -- in 10 minutes and 22 seconds, at a cost of $1.73 in API usage. A human expert, using professional tools, required approximately 12 hours. On AISI's battery of advanced cybersecurity tasks, GPT-5.5 achieved an average pass rate of 71.4% on the most difficult "Expert" tier, edging out Mythos Preview at 68.6% percent and significantly surpassing GPT-5.4 at 52.4%. The findings carry pointed implications for the broader trajectory of AI development. AISI concluded that GPT-5.5's performance suggests rapid improvement in cyber capabilities may be part of a general trend rather than an isolated breakthrough -- and warned that if offensive cyber skill is emerging as a byproduct of wider improvements in reasoning, coding, and autonomous task completion, then further advances could arrive in quick succession. The report also flagged significant concerns about the model's safety guardrails. Researchers identified a universal jailbreak that elicited harmful content across all malicious cyber queries tested, including in multi-turn agentic settings. The attack took six hours of expert red-teaming to develop. OpenAI subsequently updated its safeguard stack, though a configuration issue prevented AISI from verifying whether the final version was effective. AISI cautioned that its capability evaluations were conducted in a controlled research environment and do not necessarily reflect what is accessible to an ordinary user, noting that public deployments include additional safeguards and access controls. The report lands against a worrying backdrop for British cybersecurity. The U.K. government's annual Cyber Security Breaches Survey, also published Thursday, found that 43% of businesses suffered a cyber breach or attack in the past 12 months. In response, the government announced £90 million in new funding to boost cyber resilience, and said it is moving forward with the Cyber Security and Resilience Bill to protect essential services. Officials also published guidance urging organizations to prepare for a potential surge in newly discovered software vulnerabilities as AI accelerates the pace at which security flaws can be found and weaponized.

OpenAI expands Trusted Access program with GPT-5.5-Cyber

OpenAI has begun the rollout of GPT-5.5-Cyber, an AI model focused on cybersecurity, aiming to deliver it to "critical cyber defenders" within days. This initiative follows Anthropic's announcement of Claude Mythos Preview, a model found to autonomously discover numerous software vulnerabilities, which was deemed too dangerous for public release. CEO Sam Altman stated, "We're starting rollout of GPT-5.5-Cyber to critical cyber defenders in the next few days." He emphasized collaboration with the government and the broader ecosystem to ensure trusted access and security for companies and infrastructure. The rollout is part of a comprehensive cybersecurity action plan by OpenAI, structured around five key pillars: democratizing access to cyber defense tools, coordinating with government and industry, enhancing safeguards around advanced capabilities, ensuring deployment visibility, and enabling user self-protection. The new model builds on GPT-5.4-Cyber, which was introduced in mid-April as part of OpenAI's Trusted Access for Cyber program, alongside $10 million in API grants for vetted security organizations. In contrast to Anthropic's more limited approach, which restricted Mythos to around 50 organizations in a controlled program, OpenAI plans to distribute GPT-5.5-Cyber more broadly. The model will be made available through the Trusted Access for Cyber (TAC) program to government entities, critical infrastructure operators, security vendors, cloud platforms, and financial institutions. Anthropic's model, Claude Mythos Preview, announced earlier in April, demonstrated advanced capabilities by discovering thousands of new zero-day vulnerabilities. It autonomously created exploits, showcasing improvements in reasoning and coding capabilities, including constructing a full browser exploit and a FreeBSD remote code execution exploit through complex vulnerability chaining. While Anthropic has committed up to $100 million in usage credits and $4 million in donations to open-source security organizations, it has stated that Mythos will not be publicly available. Subsequently, the company released a less capable model, Claude Opus 4.7, whose cybersecurity features are "not as sophisticated" as those of Mythos. OpenAI has yet to publish technical benchmarks comparing GPT-5.5-Cyber to Mythos. The base model received a "High" rating on OpenAI's cybersecurity risk scale, falling below the "Critical" threshold needed for developing zero-day exploits autonomously without human intervention. The effectiveness of the Cyber-specific variant in closing this gap remains uncertain, as leading security professionals express concerns that the ability to find software flaws at scale is increasingly difficult to contain.

OpenAI Confirms GPT-5.5 Cyber Model's Rollout Is Around the Corner

The new model comes less than a month after GPT-5.4 Cyber's release OpenAI CEO Sam Altman teased the successor to the GPT-5.4 Cyber artificial intelligence (AI) model on Thursday. Dubbed GPT-5.5 Cyber, the model was announced just a fortnight after the San Francisco-based AI giant introduced its first cybersecurity model. Not a lot is known about the model currently, but it is expected to follow the same limited release format as the predecessor. The model is said to be competing with Anthropic's Claude Mythos, and offers similar real-world vulnerability detection prowess. OpenAI Teases GPT-5.5 Cyber In a post on X (formerly known as Twitter), Altman shared that GPT-5.5 Cyber will soon be rolled out to critical cyber defenders. Interestingly, the company is also hosting a GPT-5.5 "party" at its San Francisco headquarters on May 5. The company had asked users to sign up to get a chance to attend it. There's a possibility that OpenAI might preview some of the capabilities of 5.5 Cyber during the event. For now, not a lot is known about the large language model (LLM). Besides teasing the early access rollout, the OpenAI CEO said, "We will work with the entire ecosystem and the government to figure out trusted access for cyber; we want to rapidly help secure companies/infrastructure." The restricted rollout makes sense. When the company released the GPT-5.4 Cyber model, it was designed for cybersecurity functions. It used binary reverse engineering capabilities to analyse compiled software for malware potential, vulnerabilities, and overall security. OpenAI had said that the model does not even require access to the source code of a software to analyse this. Based on this, it appears that the model's functionality is broadly similar to Anthropic's Claude Mythos. To ensure that the cybersecurity LLM would not be misused, the AI giant scaled its Trusted Access for Cyber (TAC) programme, which only lets the model be accessed by verified individuals and firms. Since little is known about the capabilities of the GPT-5.5 Cyber AI model, it cannot be said with certainty that it can outperform Claude Mythos. However, once OpenAI releases the system card and internal evaluations, the comparison between the two will become clearer.

OpenAI Will Arm Critical Cyber Defenders With Frontier Model | PYMNTS.com

By completing this form, you agree to receive marketing communications from PYMNTS and to the sharing of your information with our sponsor, if applicable, in accordance with our Privacy Policy and Terms and Conditions. "We will work with the entire ecosystem and the government to figure out trusted access for cyber; we want to rapidly help secure companies/infrastructure," Altman wrote. OpenAI announced in a Wednesday blog post that the company released an Action Plan that describes how it will build the infrastructure needed to support cybersecurity defenders and will provide trusted actors across society with access to defensive tools. The company's plan includes democratizing cyber defense, coordinating across government and industry, strengthening security around frontier cyber capabilities, preserving visibility and control in deployment, and enabling users to protect themselves. OpenAI said in its post that as AI reshapes cybersecurity, criminals are deploying the same capabilities as defenders. "Building resilience in the Intelligence Age will require both working through democratic institutions and processes, and broadening access to the technologies that can help protect communities, critical systems and our national security," OpenAI said in the post. It was reported April 21 that OpenAI has begun briefing state and federal government officials on the capabilities of its cybersecurity product. The AI startup held an event in Washington, D.C., where it demonstrated a new model to officials from throughout the government and from various national security agencies. The company is taking a dual-track approach, making one version of its model more widely available with robust safeguards, and another more permissive version for cyber defenders through its Trusted Access program. This tactic will let more companies, like local water utilities, access advanced AI tools. OpenAI said April 14 that it plans to expand access to the Trusted Access for Cyber (TAC) program, which it introduced in February, to give cybersecurity professionals access to frontier models. The company said it is scaling up TAC to thousands of verified individuals and hundreds of teams responsible for defending critical software. "In preparation for increasingly more capable models from OpenAI over the next few months, we are fine-tuning our models specifically to enable defensive cybersecurity use cases, starting today with a variant of GPT-5.4 trained to be cyber-permissive: GPT-5.4-Cyber," OpenAI said in an April 14 blog post.