A comparison of GLM-5.3 and Claude Fable 5 on the DeepSWE benchmark reveals that while both models achieve near-identical first-shot accuracy (69.0% vs 69.7%), GLM-5.3 is significantly more cost-effective and performs better in multi-attempt scenarios.

  • GLM-5.3 costs $3.99 per rollout compared to Fable 5's $21.63, a 5.4x price gap that results in 17 solves per $100 versus Fable's 3.
  • In multi-attempt metrics, GLM-5.3 leads with pass@2 at 81.1% (vs 77.1%) and pass@4 at 87.6% (vs 84.1%), demonstrating a higher ceiling.
  • The models are near-substitutes with a per-task correlation of 0.65, meaning running both adds little coverage diversity.
  • GLM-5.3 wins five task domains including concurrency and durability, while Fable 5 leads only in Rust (85% vs 70%) and serialization-heavy work.

The analysis concludes that GLM-5.3 should be the default model for most software engineering tasks due to its lower cost and broader coverage, with Fable 5 reserved as an expensive escalation path specifically for Rust or serialization-critical work.