Claude Fable 5.2 builds a working operating system with 1,000 agents in eight days

Anthropic’s newest Claude models have taken on engineering challenges that typically demand extensive human expertise and months of work. Claude Fable 5.2 and Claude Mythos 5.2 have demonstrated significant improvements across software development, robotics, mathematics, and theoretical physics. During internal testing, Fable 5.2 coordinated more than 1,000 agents to build a working operating system. The model also helped researchers tackle two previously unresolved problems involving black holes. In another experiment, it completed a computer-verifiable formalization of Fermat’s Last Theorem in just 30 hours. These results suggest the models can handle increasingly complex technical assignments. Anthropic says both versions share the same underlying architecture. However, Mythos targets vetted cybersecurity and biomedical research organizations. Working operating system One of the more striking experiments involved building an operating system from scratch. An Anthropic engineer gave Fable 5.2 a basic prompt and an empty project folder. The model coordinated more than 1,000 subagents over eight days. They wrote code, tested components, and reviewed their work throughout the process. The resulting operating system could boot on a laptop. It included its own kernel, hardware drivers, and permanent file storage. It also featured a graphical interface, login screen, installer, and built-in Claude functionality. Introducing Claude Fable 5.2 and Claude Mythos 5.2, designed to tackle the most daunting technical challenges.They’re capable collaborators on ambitious projects in many fields, and show improvements in areas like coding, reasoning, and vision. pic.twitter.com/jP0AutLxXb— Claude (@claudeai) November 9, 2026 Software engineering wasn’t the only area where Fable 5.2 demonstrated its capabilities. Anthropic also tasked it with designing three electronic devices. These included a home voice-assistant hub, a USB speakerphone, and a handheld virtual pet. The model selected components from US distributors and designed circuit boards. It also created 3D-printed enclosures and wrote the required software. All three devices worked without electrical modifications. Their circuit boards reached manufacturing readiness in less than a day. Anthropic also reported a striking result from an internal software migration. A team of agents moved a critical production service from Python to Rust. The resulting service now starts approximately 26 times faster. Stronger robotics and security Fable 5.2 also demonstrated substantial improvements in controlling physical robots. On the RoboDojo benchmark, it achieved a 64.9 percent success rate. That represents a significant jump from Fable 5.1’s 27.6 percent score. It also outperformed GPT-6 Astra, which recorded 29.8 percent on the same evaluation. Opus 5.5 reached 39.4 percent. The benchmark tests how models control a simulated two-arm robot using camera images. Demonstrations included solving puzzle cubes, opening bottle caps, and drawing pictures. Cybersecurity results offered another notable performance gain. Anthropic’s specialized Mythos 5.2 model achieved an 89.6% score on its CVE Rediscovery evaluation. That represents a 10.2 percent improvement over Opus 5.5. It also marks an 11.3 percentage-point increase over Mythos 5.1, which scored 78.3 percent. A separate security company found that other tested frontier models missed one in six confirmed vulnerabilities identified by Mythos 5.2. Faster performance, fewer blocks Anthropic says Fable 5.2 and Mythos 5.2 generate outputs up to 30 percent faster than their predecessors. Their standard pricing also starts at $8 per million input tokens and $40 per million output tokens. An optional fast mode increases token generation speeds by up to 2.5 times. However, it doubles the standard pricing. The company also reports improvements to its safety classifiers. Fable 5.2 produces approximately 55 percent fewer unnecessary blocks than Fable 5.1. Cybersecurity-related blocks fell by 60 percent, while biology-related blocks declined by 40 percent. These changes should make the models less restrictive during legitimate work. Mythos 5.2, however, remains available only to vetted organizations pursuing approved cybersecurity and biomedical research. Get the latest in engineering, tech, space & science - delivered daily to your inbox.Aamir is a seasoned tech journalist with experience at Exhibit Magazine, Republic World, and PR Newswire. With a deep love for all things tech and science, he has spent years decoding the latest innovations and exploring how they shape industries, lifestyles, and the future of humanity.