Claude-Mythos

Claude Mythos is Anthropic’s most advanced AI security model, achieving a 73% success rate on expert-level CTF tasks and identifying thousands of zero-day vulnerabilities across every major OS and browser before its April 2026 release. Access is gated through Project Glasswing, a vetted defensive coalition of 12 named partners including Microsoft, Google, and CrowdStrike, plus 40+ critical infrastructure organizations. What Is Claude Mythos Preview? (And Why Anthropic Kept It Secret) Claude Mythos Preview is Anthropic’s frontier cybersecurity model — a purpose-built AI system that autonomously discovers, analyzes, and proves exploitability of software vulnerabilities at a capability level no model had reached before April 2025. Unlike Claude Opus or Sonnet, which are general-purpose assistants, Mythos was trained specifically to perform security research tasks: reading source code across millions of lines, forming hypotheses about vulnerable code paths, writing proof-of-concept exploits, and iterating until a working attack chain is confirmed. The model was kept in restricted preview for over a year before its April 7, 2026 announcement because Anthropic’s internal red teams confirmed it could assist with real-world offensive operations — including completing a 32-step corporate network attack simulation that human experts estimate would take 20 hours, in 3 of 10 controlled attempts. The decision to restrict rather than broadly release the model reflects Anthropic’s Responsible Scaling Policy: Mythos crossed an internal threshold requiring mandatory containment measures before any external access. The result is a model that is simultaneously the most powerful defensive security tool ever deployed at scale and one of the most carefully gated AI releases in the industry’s history. ...

Claude Mythos Preview leads every major coding benchmark in 2026 — 93.9% on SWE-bench Verified — but it’s locked behind Anthropic’s invitation-only Project Glasswing. GPT-5.5 (the model OpenAI shipped instead of GPT-6) scores 88.7% on SWE-bench, costs 4x less, and is available in the API today. For most dev teams, GPT-5.5 is the only frontier option that actually ships. The ‘GPT-6’ Situation: What OpenAI Actually Shipped in April 2026 GPT-5.5 is the model OpenAI launched on April 23, 2026 — the release widely expected to carry the “GPT-6” label. Instead of a major version bump, OpenAI delivered an incremental but significant upgrade codenamed “Spud” internally, positioning it as GPT-5.5 rather than GPT-6. The decision signals OpenAI’s intent to reserve the “6” designation for a substantially larger architectural leap, similar to how GPT-4 marked a clear departure from GPT-3.5. GPT-5.5 ships in three variants — standard, Thinking, and Pro — at pricing of $5/M input and $30/M output for standard, with Pro at $30/$180. The model is available via ChatGPT, Codex CLI, and the OpenAI API from day one. Key capabilities: 60% fewer hallucinations than GPT-5.4, stronger multi-step reasoning in Thinking mode, and a 82.7% score on Terminal-Bench 2.0 that narrowly edges Claude Mythos Preview. For developers evaluating this release, GPT-5.5 is the de facto frontier option available without waitlists or partner agreements — making availability as important as raw benchmark numbers. ...

Claude Mythos achieves 92% on SWE-bench Pro coding tasks — compared to 86% for Claude 3.5 Sonnet at its launch — representing a meaningful step up in autonomous software engineering capability. Early access developers report 40% productivity gains on complex programming tasks, and enterprise adoption is projected to reach 30% among Fortune 500 technology teams by end of 2026. Mythos is in developer preview as of mid-2026, accessible via the Anthropic Console for teams on the API with qualifying usage tiers. The model represents Anthropic’s next-generation architecture beyond Opus 4.7, with improvements in reasoning depth, code correctness, and multi-step agentic task completion. Here is what developers need to know before access broadens. ...