Benchmarking Opus 5 on SlopCodeBench: Analyzing Long-Horizon Coding Performance and Codebase Evolution Quality
A recent evaluation of Anthropic's Opus 5 on the SlopCodeBench benchmark, a long-horizon coding test developed by the UW Madison lab, reveals that while the model leads with a 24% pass rate, it faces significant challenges in maintaining codebase quality. Unlike traditional benchmarks that provide all requirements upfront, SlopCodeBench utilizes evolving checkpoints to simulate real-world software development. The results show that Opus 5, along with Sonnet 5 and Opus 4.8, exhibits significant increases in verbosity and "code smell" as tasks progress. Notably, Opus 5 produced five times the number of functions compared to Opus 4.8 for the same challenges. These findings suggest that current AI models still face substantial hurdles in simulating the iterative nature of professional software engineering.







