Originally published on NextFuture

As of May 2026, Anthropic's Mythos and OpenAI's GPT-5.5-Cyber sit behind allowlists that most engineering teams will never clear. Meanwhile, Llama Guard 3, CodeLlama Guard, and Cisco AI Defense have been in production for months—no NDAs, no federal vetting, no undisclosed pricing. We tested both stacks against four real defensive tasks: phishing detection, code audit, threat triage, and log forensics. Here is what the gap actually looks like. For the broader context on how these models came to exist, see Inside the AI Cyber Arms Race (May 2026) .

TL;DR: which one wins

Verdict dimensionClosed Frontier (Mythos / GPT-5.5-Cyber)Open Defensive Stack (Llama Guard 3 + CodeLlama Guard)

AccessAllowlist only (~40 orgs, May 2026)Public API + self-hostable today Best taskAdversarial simulation, advanced threat-intel synthesisPhishing detection, code audit, content filtering PriceUndisclosed (federal/enterprise contracts)$0–$0.60/1M tokens; free if self-hosted VerdictWorth pursuing…