Anthropic's next Mythos-class model will debut with an HLE Accuracy below 60 percent. That outcome will leave Mythos behind the current HLE leaders, where Claude Opus 5 led at 64.7 percent on BenchLM.ai as of August 31, 2026 and Claude Mythos 5 sat at 64.5 percent on the same board. Claude Fable 5.…