Claude Fable 5 vs GPT-4o for TypeScript Codegen

Short summary

A head-to-head comparison of Claude Fable 5 and GPT-4o on realistic TypeScript generation tasks using a three-gate rubric: clean compilation, strict mode compliance, and graceful error handling. Claude Fable 5 excels with generics and async error boundaries but stumbles on deeply nested discriminated unions. GPT-4o is solid on intermediate patterns but drops exhaustiveness checks and leaves unhandled promise rejections. The practical takeaway: match the model to your codebase's dominant failure mode.

• •Claude Fable 5 is stronger with generics, utility types, and async error handling
• •GPT-4o is consistent on simple/intermediate types but drops exhaustiveness checks and unhandled rejections
• •Both models need human review on discriminated unions with more than 2-3 variants

Generated with AI, which can make mistakes.