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Our evaluation of OpenAI's GPT-5.5 cyber capabilities

sourceSimon Willison
calendar_todayMay 1, 2026
schedule1 min read
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EXECUTIVE SUMMARY

Evaluating OpenAI's GPT-5.5: A New Player in Cybersecurity

Summary

OpenAI's GPT-5.5 has been evaluated for its cyber capabilities, particularly in identifying security vulnerabilities. This assessment positions GPT-5.5 as a competitive alternative to Claude Mythos, which was previously evaluated by the UK's AI Security Institute.

Key Points

  • The UK's AI Security Institute conducted an evaluation of GPT-5.5 for security vulnerability detection.
  • GPT-5.5 is found to be comparable to Claude Mythos in its capabilities.
  • Unlike Claude Mythos, GPT-5.5 is generally available for use.
  • The evaluation highlights the growing role of generative AI in cybersecurity.
  • OpenAI is the developer of GPT-5.5, contributing to advancements in AI security research.
  • The evaluation reflects ongoing trends in AI and machine learning applications in IT security.

Analysis

The evaluation of GPT-5.5 by the UK's AI Security Institute underscores the increasing integration of generative AI in cybersecurity. With its capabilities being on par with established models like Claude Mythos, GPT-5.5 presents a significant tool for IT professionals in identifying and mitigating security vulnerabilities.

Conclusion

IT professionals should consider leveraging GPT-5.5 for enhanced security vulnerability detection, especially given its availability and comparable performance to existing solutions. Staying informed about advancements in AI capabilities will be crucial for maintaining robust cybersecurity measures.