GLM-5.3 vs. Claude Fable 5 on DeepSWE: Cost, Coding, and Routing

This post compares GLM-5.3 and Claude Fable 5 on the DeepSWE benchmark, focusing on accuracy, cost, and specific task/language performance. GLM-5.3 demonstrates comparable first-shot accuracy to Fable 5 but at a 5.4x lower cost, with better performance on retries and wider domain coverage. Fable 5 shows a distinct advantage in Rust and serialization tasks. The analysis highlights their high per-task correlation, suggesting they are near-substitutes, and recommends GLM-5.3 as the default with Fable as a specialized escalation.