UK AI Safety Institute Evaluates GPT-5.5's Cybersecurity Capabilities
UK AISI finds GPT-5.5 matches Claude Mythos in cybersecurity skills, but is already publicly available.
The UK AI Safety Institute (AISI) has evaluated OpenAI's GPT-5.5 and found its cybersecurity vulnerability discovery capabilities comparable to Anthropic's Claude Mythos. The critical distinction is that GPT-5.5 is already publicly available, raising urgent questions about AI governance, capability thresholds, and the balance between offensive and defensive use of AI in cybersecurity.
Overview
The UK AI Safety Institute (AISI) recently published its assessment of the cybersecurity capabilities of OpenAI's latest model, GPT-5.5. The institute had previously conducted a similar evaluation of Anthropic's Claude Mythos. The results show that GPT-5.5's ability to discover security vulnerabilities is comparable to Claude Mythos — but there's a critical difference: GPT-5.5 is already available to the public.
Assessment Background
AISI's Role and Mission
The UK AI Safety Institute is one of the first government bodies in the world to conduct systematic safety evaluations of frontier AI models. Its core mission is to assess potential risks and capability boundaries before AI models are widely deployed, with a particular focus on high-risk domains such as cybersecurity and biosecurity.
Why AI's Cybersecurity Capabilities Matter
As large language models rapidly grow more capable, AI's double-edged nature in cybersecurity has become increasingly apparent. On one hand, AI can help defenders discover and patch vulnerabilities faster. On the other hand, attackers could leverage AI to automate the discovery and exploitation of security flaws. Evaluating frontier models' offensive cyber capabilities is therefore essential for developing sound AI governance policies.
Assessment Results
GPT-5.5 Matches Claude Mythos in Capability
AISI's evaluation shows that GPT-5.5's performance in discovering security vulnerabilities is on par with Anthropic's Claude Mythos. This suggests that today's most advanced large language models are converging in their cybersecurity capabilities, with top-tier models from different vendors exhibiting similar capability ceilings.
The Key Difference: Availability
However, there is one important distinction between the two. Claude Mythos had not yet been publicly released at the time of its evaluation, whereas GPT-5.5 is already available to the public. This difference carries significant policy implications — a model with substantial cybersecurity capabilities is already being widely used in the real world, making the development of risk assessments and protective measures all the more urgent.
Deeper Implications
Rapid Evolution of AI Cybersecurity Capabilities
From GPT-4 to GPT-5.5, AI models have made notable strides in understanding code logic, recognizing security patterns, and identifying potential vulnerabilities. These improvements extend beyond simple code review to include comprehension of potential attack surfaces within complex system architectures.
Implications for AI Governance
This assessment highlights several key issues:
- Timing of Evaluations: The importance of conducting safety assessments before public release goes without saying, but when a model is already publicly available, the manner and timing of publishing evaluation results require even greater care
- Capability Thresholds: The industry needs to establish clearer standards that define at what level of AI cybersecurity capability additional safety measures are required
- International Collaboration: Cybersecurity threats are global in nature, making information sharing and coordinated assessments among national AI safety bodies increasingly important
Balancing Defense and Offense
It's worth noting that the same capabilities can be used for both attack and defense. GPT-5.5's ability to discover vulnerabilities means security researchers can leverage it to accelerate vulnerability discovery and remediation, thereby improving overall cybersecurity. The key lies in ensuring that these capabilities are predominantly used by defenders.
Conclusion
AISI's evaluation of GPT-5.5 provides an important reference point: publicly available AI models have already achieved a significant level of capability in discovering cybersecurity vulnerabilities. This represents both an opportunity and a challenge, requiring the entire industry to build more robust safety evaluation frameworks and risk management mechanisms while continuing to advance AI capabilities.
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