Claude Fable 5 Cracks String Theory Problem Overnight, Anthropic and OpenAI Engage in Credit War

Recently, Anthropic's flagship model Claude Fable 5 has demonstrated remarkable capabilities across multiple domains, sparking a new round of competition in the AI industry.

Scientific Breakthrough: Fable 5 Solves String Theory Problem

Yuji Tachikawa, a mathematical physicist at the University of Tokyo, shared on social media that he used Claude Fable 5 to help solve a string theory research problem that had stumped him for half a year. Fable 5 not only identified calculation errors but also proposed new approaches and proactively used SymPy to write code to verify predictions. Tachikawa commented, "It seems to truly understand string theory and also has intuition." This case was reported by Nature and is considered a milestone in AI-assisted scientific research.

Additionally, Stanford geneticist Euan Ashley used Claude to interpret his own genome, completing the task in 30 minutes, whereas in 2010, he led a team of 31 people that took 9 months to complete the first clinical genome interpretation.

Product Capabilities: All-Round Performance from Code to Images

In the developer community, Fable 5 has been used to quickly build complex applications. For example, one developer used Fable 5 to regenerate the 2003 classic game "Command & Conquer" into a native iOS version within hours. Another developer used Fable 5 and Opus 4.8 to create a Windows image toolbox called JImage, integrating dozens of features such as screenshot, editing, AI image generation, and batch processing, showcasing the model's execution capability in long-chain tasks.

Intensified Competition: The Credit Game Between Anthropic and OpenAI

Facing the cost-effectiveness advantage of OpenAI GPT-5.6 Sol, Anthropic has repeatedly extended the free access period for Fable 5 and increased the weekly limit for Claude Code by 50%. OpenAI, in turn, removed the 5-hour usage limit, optimized Sol's consumption, and reset user credits. Both companies are competing for users by adjusting "credits" rather than lowering prices, with developers constantly switching between the two.

Talent Movement: Claude Design Lead Joins Cursor

Jenny Wen, the core design lead for Claude, announced her departure from Anthropic to join Cursor, which was acquired by SpaceXAI, as Head of Design. She previously led the visual overhaul of Claude.ai and the design of the universal agent Cowork. Her move is seen as a signal that AI coding tools are shifting from engineering capabilities to user experience.

Industry Impact

The scientific breakthroughs and product capabilities of Fable 5 indicate that AI is transitioning from a tool to a "colleague." Meanwhile, the credit war between Anthropic and OpenAI reflects that competition among large models has shifted from pure capability comparison to balancing cost and accessibility.