Open-source tax engine scores 96% on TaxCalcBench and tops GPT Sol

Intelligent_Prompt18 · reddit · 2026-07-24

Open-source tax engine beats GPT Sol and Fable 5 on TaxCalcBench

An open-source deterministic tax engine reportedly reached 96% on TaxCalcBench, the highest score claimed in the thread, and beat both GPT Sol and Fable 5 using only Claude Sonnet 5 via MCP.

The author says the engine is meant for research and tax prep, reducing guesswork and calculation mistakes. They also note that the two misses were caused by inconsistencies in the benchmark itself, which the maintainers allegedly confirmed.

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