Product UpdatesBuilding Sheldon's State Tax Engine: 98% on TaxCalcBench
Deterministic rule engines for California, Illinois, New York, and Virginia - 620 of 630 scored lines on TaxCalcBench, every gap a documented benchmark defect.

Illinois & Virginia join the Feather KB. File Viewer, CSV, Excel tools improved, and the Gemini 3.6 upgrade.
As we approach the end of August, this is another big update on Feather. In the past two weeks the team has been on-and-off enjoying their summer vacations. While we recharged, we shipped some of most-requested upgrades for the Feather Tax KB. Read on for the details!
Feather Tax Knowledge Base now includes two new jurisdictions for research answers:
Coverage also expanded for California and New York:
IRS Newsroom releases are also now indexed, so Feather picks up new IRS guidance as it is published.
The right side panel in the Chat and the Safe now shows extracted-text tabs, knowledge base citations, and the original document together in a unified way.
Moreover we've updated the way Feather handles CSV and Excel files. CSV files can now be edited in Feather. Excel (.xlsx) files render in the browser without CSV or Markdown conversion.
Feather Tax Assistant is now powered by the latest Gemini 3.6 AI—smarter, quicker, and of course, Section 7216 compliant. You’ll notice answers are clearer, more accurate, and straight to the point.
Two issues of the Feather Tax Brief published earlier this month:
That's all for this week. New here? Try Feather free, see pricing, or subscribe to the Feather Tax Brief for weekly IRS guidance. Take care!
Product UpdatesDeterministic rule engines for California, Illinois, New York, and Virginia - 620 of 630 scored lines on TaxCalcBench, every gap a documented benchmark defect.
Product UpdatesA deterministic tax calculator built on a dedicated knowledge base and AI-generated rules - and how it went from 50% to 190/190 on TaxCalcBench.
Product Updates
Written by Danko Komlen, Sokratis Vidros
Published on August 24, 2026