In the wake of Anthropic’s announcement of its latest artificial intelligence model, Mythos, on April 7, the company has stood by an unusual decision: refusing to release it to the public. Not since OpenAI temporarily withheld its GPT-2 model in 2019 has a major developer deemed a system too dangerous for the public. More than a week later, that choice is still reverberating through finance and regulatory circles. “The fallout—for economies, public safety, and national security—could be severe,” Anthropic said on its website. But while officials scramble to gauge the implications of the model’s unprecedented hacking capabilities, cybersecurity experts are divided over whether Mythos marks a major break from what came before or an expected step down an already troubling path. Anthropic did not respond to a request for comment from Scientific American. On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. A 245-page technical document released alongside the announcement outlines what the company presents as a major leap in capability. The model operates like a senior software engineer, demonstrating an ability to spot subtle bugs and self-correct mistakes. It also scored 31 percentage points higher than Anthropic’s previous cutting-edge model, Opus 4.6, on the USAMO 2026 Mathematical Olympiad, a grueling, two-day proof-based competition. But that same coding prowess makes Mythos a formidable offensive weapon, and Anthropic says it can outstrip all but the most skilled humans at identifying and exploiting software vulnerabilities. In tests, it found critical faults in every widely used operating system and web browser. Of those vulernabilities, 99 percent have not yet been patched. And Anthropic has disclosed only a fraction of what it says it