Frontier AI at a cost: what Anthropic’s Fable 5.1 means for the US-China model race

Anthropic’s powerful new Claude Fable 5.1 model has widened its lead in performance benchmarks over Chinese rivals, even as budget-friendly open-weight models from China continue to gain commercial traction globally.

The American company said on Wednesday that Fable 5.1, along with a restricted-access version called Mythos 5.1, was the world’s most advanced model for software coding and complex knowledge work.

The standard version scored 66 on Artificial Analysis’ Intelligence Index, taking the top spot globally and pulling six points clear of Moonshot AI’s Kimi K3 and Z.ai’s GLM-5.3, both leading Chinese models.

Fable 5.1 also claimed first place on San Francisco-based Vals AI’s index for handling complex, real-world tasks across sectors such as finance, coding and law. Anthropic’s earlier Opus 5 and Fable 5 models trailed closely in second and third place.

The benchmark results prompted industry insiders to weigh in on whether leading labs in the United States were pulling further ahead of Chinese competitors.

Yuchen Jin, a technical staff member at US artificial intelligence platform Databricks, called Fable 5.1’s capability leap “insane”, while some observers noted its performance shattered claims that Chinese open-weight developers had already closed the gap with the frontier.

However, a stark price gap points to a sharp divide between the two countries’ approaches.