Claude Fable 5 vs GPT-5.5: AI Model Comparison & Benchmarks

Anthropic has released Claude Fable 5, its first publicly available model, alongside Mythos 5. This new model is designed to handle complex reasoning, coding tasks, and extended workflows. What's interesting is that the more powerful Claude Mythos preview model remains restricted from public access due to misuse concerns. However, the publicly released Fable 5 is said to rival OpenAI's ChatGPT 5.5, their most capable model. When it comes to coding, benchmarks show Claude Fable 5 with a noticeable edge. On SWE-Bench Pro, Fable 5 scored 80.3%, while GPT-5.5 scored 58.6%. Anthropic also reports a substantial lead on FrontierCode Diamond. Real-world testing by Stripe even saw Fable 5 complete a codebase-wide migration in one day. OpenAI highlights GPT-5.5's 82.7% score on Terminal-Bench 2.0 and gains in token efficiency for coding tasks. For knowledge work, Claude Fable 5 achieved a score of 1932 on GDPval-AA, a benchmark for professional and analytical work, compared to GPT-5.5's 1769. Understanding these differences can help you determine which AI model is best for your specific needs.