Claude Mythos Preview

Anthropic says Claude has assessed conversations for potential misuse after responding since June. It reports detecting 94% of high-priority cases flagged by a stronger classifier at a 1% false-positive rate.

Anthropic reports that GLM-5.3 produced working browser exploits in 50 of 410 controlled attempts. In a separate binary-exploitation test, it achieved control-flow hijacks in 4% of trials.

Anthropic published internal metrics showing Claude wrote 80% of merged code, with 8x engineer output and 52x training-code speedups in Mythos Preview. The post matters because it gives a rare lab-side look at AI-assisted engineering gains, while still saying research judgment remains a bottleneck and recursive self-improvement is unproven.

Anthropic widened Project Glasswing from roughly 50 to about 200 vetted organizations, expanding access to Claude Mythos Preview for defensive security work. The program keeps Mythos restricted while Anthropic argues AI-assisted exploit discovery is accelerating.

Anthropic staff and outside observers said a Mythos-powered Claude Code setup solved Erdős problem #90 in an internet-blocked test. The result is still based on harnessed runs and social-thread disclosures, so watch for fuller verification before treating it as settled.

Watchers spotted claude-mythos-1-preview references in Claude, Claude Code, and Claude Security, with one screenshot also showing adaptive thinking. That matters because Anthropic appears to be testing a coding- and security-focused access path before any wider rollout.

METR said an early Claude Mythos Preview snapshot reached at least a 16-hour 50% time horizon, with only five tasks in-suite at that range. The result matters because Mythos is beyond METR's stable measurement band, so cross-model comparisons are less reliable.

Mozilla says Claude Mythos Preview helped it fix more Firefox security bugs in April than in the previous 15 months combined. Teams building large codebases should watch this as a strong production example of frontier models accelerating defensive vulnerability work.

Anthropic introduced Natural Language Autoencoders, a two-model method that translates Claude activations into text explanations and reconstructs them back. The system exposed hidden rhyme planning and evaluation awareness in Claude, but Anthropic says the explanations are useful rather than guaranteed faithful.

Posts summarizing WSJ reporting say Anthropic’s push to widen Mythos preview access by about 70 organizations was opposed over national-security and compute-capacity concerns. The change matters because access to Anthropic’s top cyber model may stay tightly rationed for defenders, vendors, and evaluators.

Multiple summaries of the UK AISI report say GPT-5.5 roughly matches Claude Mythos Preview on long-horizon cyber tasks, including 2 of 10 end-to-end TLO completions. That matters because the model is broadly usable today, shifting cyber-workflow choices toward availability and mitigations rather than gated access alone.

Anthropic's Mythos system card says the model completed the AI Security Institute's 32-step corporate attack range in about 20 human hours. The benchmark matters as a cyber capability signal, but the range is easier than a real defended enterprise network.

UK regulators put Claude Mythos on formal briefing agendas while US officials also pushed banks to evaluate it. Watch the independent critiques of Anthropic's exploit method, low-level access behavior, and small-model comparisons before treating the release as production-ready.