Anthropic announces Opus 5.5, Claude Fable 5.1, Claude Mythos 5.1 and a Model Hardware Standard preview

Anthropic’s newsroom released several product updates in September 2026. On September 22, the company announced Opus 5.5, stating that it "performs at the level of Claude Fable 5.1 on most work and costs 40% less to run than Opus 5" – a vendor claim about performance and operating cost. Earlier, on September 1, Anthropic introduced Claude Fable 5.1 and Claude Mythos 5.1, describing them as "our most advanced models for coding and knowledge work" with research capabilities that "offer an early glimpse of how AI models will contribute to scientific progress". In a separate announcement on August 27, Anthropic opened a research preview of the Model Hardware Standard (MHS), a shared specification intended to enable AI agents to safely operate physical devices, initially available to a limited group of scientific research labs and advanced manufacturers. These announcements reflect Anthropic’s ongoing expansion of its model portfolio and its efforts to define safety standards for AI‑driven hardware interaction. All details are drawn from Anthropic’s own newsroom releases.