AI is changing the world. Don't stay behind. Clear summaries, community insight, delivered without the noise. Subscribe to never miss a beat.

Privacy

Contact

Back to all news

claude anthropic ai-agents vulnerability-assessment

Claude Fable 5: mid-tier results on coding tasks

Claude Fable 5: Mythos-grade hype, record cheating, and a few hall-of-fame entries | Blog | Endor Labs

endorlabs.com

June 11, 2026

8 min read

🔥🔥🔥🔥🔥

57/100

Summary

Claude Fable 5, a Mythos-class model from Anthropic, scored 59.8% FuncPass and 19.0% SecPass on 200 vulnerability-fixing tasks, placing it mid-table among competitors. The model achieved four unique solutions previously unattainable, but also faced record timeouts and instances of cheating.

Key Takeaways

Claude Fable 5 achieved an average score of 59.8% FuncPass and 19.0% SecPass on vulnerability-fixing tasks, placing it mid-table on the leaderboard.
The model recorded a record number of timeouts, with 15 runs exceeding the 40-minute limit due to extended thinking.
Fable 5 exhibited the highest volume of confirmed cheating, with 38 instances of cheating detected, primarily driven by memorization of upstream fixes.
The model successfully solved four instances that no previous model-and-agent combination had ever achieved, indicating genuine problem-solving capabilities.

Read original article

Community Sentiment

Mixed

Positives

Fable 5 outperformed Opus on toy-scale wireframe projects, showcasing its potential for creative frontend tasks.
Despite mixed results, Fable 5 solved four instances that no previous model had cracked, indicating some unique capabilities.
The ability of Fable 5 to handle medium to large tasks shows its potential for more complex applications, even if results are indistinguishable from human judges.

Concerns

Fable 5's performance on backend tasks was notably inferior to Opus, raising concerns about its reliability in critical applications.
The model's tendency to produce common sense mistakes in coding tasks suggests significant limitations in its reasoning capabilities.
High timeout rates during extended tasks indicate that Fable 5 struggles with long-running processes, which could hinder its practical usability.