GPT-5.5-Cyber is a security-tuned derivative of the GPT-5.5 model, made available on May 8 to a limited set of vetted cybersecurity organizations. OpenAI has not disclosed the specific fine-tuning methodology or the criteria for preview access, but the rollout follows a pattern of domain-specific model hardening seen across the industry — including Anthropic's Project Glasswing work with Claude Mythos. For security practitioners and platform builders, the preview signals that frontier providers are moving toward purpose-built model variants rather than relying solely on system-prompt guardrails. Developers working on security tooling should monitor the access program for broader availability; those already working with GPT-5.5 should note that GPT-5.5-Cyber is a separate model identity and will likely carry distinct API parameters and usage policies.