The UK's AI Security Institute has evaluated OpenAI's GPT-5.5 for vulnerability detection. Comparable to Claude Mythos, this model is already accessible, marking a significant advance in AI tools dedicated to cybersecurity.
A Major Breakthrough for GPT-5.5 in Vulnerability Detection
On April 30, 2026, the UK's AI Security Institute (AISI) published an in-depth evaluation of OpenAI's GPT-5.5 performance in the field of cybersecurity. This analysis follows a previous study by the same institute focused on Claude Mythos, an AI developed by Anthropic, renowned for its advanced cybersecurity capabilities. According to AISI, GPT-5.5 demonstrates performance comparable to Claude Mythos in identifying vulnerabilities, but with a key advantage: its immediate accessibility to the general public.
This general availability of GPT-5.5 represents a significant milestone, contrasting with the more exclusive and limited nature of Mythos to date. This fact raises important implications for IT security professionals and researchers, who can now leverage a powerful model without waiting for restricted openings or reserved access.
Concrete Capabilities and Comparison with Claude Mythos
In practice, GPT-5.5 proves capable of analyzing code and identifying potential flaws as effectively as Claude Mythos, according to criteria defined by AISI. This evaluation is based on a series of tests simulating realistic security scenarios, where the AI must detect vulnerabilities in diverse software environments. GPT-5.5’s comparable performance suggests a high technological maturity, notably in contextual and technical understanding of flaws.
Unlike Mythos, whose use remains limited to certain partners and use cases, GPT-5.5 is already integrated into accessible platforms, which could democratize AI usage in cybersecurity. This availability facilitates direct integration into audit workflows, pentesting, and cybersecurity training.
It is important to note that the evaluation was conducted by a recognized institute, using a rigorous methodology, lending high credibility to the conclusions. This allows GPT-5.5 to be considered not only as a support tool but as a potential leading player in securing digital systems.
Under the Hood: Technical Innovations and Architecture
Although precise technical details of the GPT-5.5 model remain confidential, it is established that it relies on a transformer-type architecture, optimized for large-scale natural language processing. OpenAI has continued to refine its training, notably by incorporating cybersecurity-specific data, which explains its enhanced performance in this sector.
This sector specialization is a strong trend in AI model development, which tends to adapt to the precise needs of professional users. GPT-5.5 thus appears to benefit from targeted training combined with a general capacity for textual understanding, enabling it to excel in code analysis and vulnerability detection.
Moreover, the model’s robustness in generating precise diagnostics without producing excessive false positives is a key asset for its adoption in sensitive environments. This operational efficiency reflects a technical maturity that surpasses previous GPT versions.
Access and Usage Modalities for Professionals
Unlike Claude Mythos, whose availability remains controlled, GPT-5.5 is accessible via OpenAI’s APIs, open to a wide range of users. Companies, researchers, and cybersecurity experts can thus integrate this model directly into their internal tools or audit platforms.
This openness facilitates the rapid deployment of automated flaw analysis solutions, helping accelerate detection and correction cycles. The real-time accessibility of GPT-5.5 also allows for its use in operational contexts, such as continuous monitoring of critical infrastructures.
Market Impact and Competition
This evaluation positions GPT-5.5 as a direct competitor to Claude Mythos, previously considered a standard for cybersecurity-specialized AIs. The immediate availability of GPT-5.5 could reshuffle the cards in this segment, strengthening OpenAI’s presence in a strategic domain.
For European and French stakeholders, this development underscores the importance of monitoring and rapidly integrating these technologies to avoid falling behind. The openness of GPT-5.5 facilitates adoption and could accelerate the digital transformation of security processes, offering a competitive advantage to organizations able to leverage these advanced tools.
Our Perspective: A Promising but Watchful Step
The confirmation by AISI of GPT-5.5’s cybersecurity capabilities marks a notable advance in the democratization of powerful AI tools dedicated to IT security. However, while performance is comparable to Mythos, it is important to keep in mind that real effectiveness will depend on operational integration and specific use cases.
Furthermore, general availability raises questions of responsibility and ethical use, notably regarding the management of detected vulnerabilities and risks related to malicious use. Nevertheless, this step opens new perspectives for AI-assisted cybersecurity, which deserves increased attention from French and European professionals.
