Open-source tax engine hits 96% on TaxCalcBench and tops Fable 5 and Sol

Intelligent_Prompt18 · reddit · 2026-07-24

An open-source tax engine reportedly hit 96% on TaxCalcBench, the highest score seen on the benchmark, beating both Fable 5 and Sol after being run with Claude Sonnet 5.

The author says the engine is deterministic and meant to reduce the guesswork and arithmetic mistakes LLMs make in tax prep and research. Its two misses were cases where the benchmark itself had inconsistencies that the maintainers later confirmed.

Related event: Open-source deterministic tax engine scores 96% on TaxCalcBench(5 posts)→

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