Additive (Thomson Reuters)
Thomson Reuters' AI extraction tool for K-1s, K-3s and related forms, with footnotes, into Excel workpapers or JSON
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About Additive (Thomson Reuters)
Additive is an AI tool that extracts data from pass-through tax documents, mainly Schedule K-1s, into Excel workpapers, JSON or PDF for accountants in the asset and wealth management space. Thomson Reuters acquired the San Francisco company, founded in 2023, in September 2025, and the site now describes it as part of Thomson Reuters.
The site lists coverage of K-1s from Forms 1065, 8865, 1041 and 1120-S, K-3s, 65 state forms including California, New York and Illinois, plus 199A, 926, 8621 and UBTI forms, with footnotes extracted rather than just the face of the form. Documents go in through the web app or directly in Excel via an add-in, and an API is available; the company says packages of tens of thousands of pages can be processed and no training is needed. Additive states SOC 2 Type 2 compliance and cites over 99% accuracy on characters of income and over 95% on footnotes, both its own figures. Crowe LLP announced in May 2026 that it had adopted the tool for K-1 processing.
It is positioned at Top 100 firms, family offices and private wealth groups with heavy pass-through workloads, rather than small practices, and has no UK tax relevance.
Key Features
- Extracts K-1s from Forms 1065, 8865, 1041 and 1120-S, plus K-3s
- 65 state forms and 199A, 926, 8621 and UBTI attachments
- Footnote extraction, not just the face of the form
- Excel add-in, web app and API; output to Excel, JSON or PDF
- SOC 2 Type 2 compliant
Our in-depth review
Additive does one job: reading Schedule K-1 packages, footnotes and all, and turning them into structured data a preparer can review. For firms serving private equity investors, family offices and wealthy individuals, that job can consume weeks of each season, and Thomson Reuters thought it worth buying.
What it does well. Depth of coverage is the main strength. Beyond K-1s from four entity types it handles K-3s, 65 state forms and the awkward attachments such as 199A, 926, 8621 and UBTI, which is where manual entry is slowest and most error-prone. Footnote extraction matters more than headline boxes. Output as Excel workpapers, JSON or PDF, plus an Excel add-in and API, means it fits existing review habits. SOC 2 Type 2 is in place, and Crowe's public adoption in May 2026 is a named, verifiable reference rather than an anonymous testimonial.
Where it falls short. The accuracy figures are the vendor's own with no published independent test. Pricing is not disclosed, and access now runs through a Thomson Reuters demo form, which tends to mean enterprise contracts and bundling conversations. Firms outside the Thomson Reuters ecosystem should ask how well it hands off to other tax engines, since the site does not name any. The product is narrow by design, so it adds a vendor and a review step rather than replacing either, and its value depends entirely on K-1 volume.
Best for. Mid-sized and large US firms, family offices and private wealth groups with heavy K-1 volumes, especially those already using Thomson Reuters tax products. In a pilot, run a few hundred of last season's hardest K-1s through it, sample the footnote output line by line, and time review rather than extraction. Abacus and K1x in this directory compete directly and are worth testing alongside; Accrual suits firms that want full draft returns rather than extraction alone. UK practices have no use for it.
Verdict. The deepest dedicated K-1 extraction tool on the market, now with Thomson Reuters behind it, held back by undisclosed pricing and self-reported accuracy.
At a glance
- Category
- Tax prep
- Best for
- 50+ practice
- Editor's score
- 4.5 / 5
- Pricing
- Custom pricing on request (demo through Thomson Reuters)
- Last verified
- 2026-10-10
Deepest dedicated K-1 extraction tool available, now backed by Thomson Reuters, held back by undisclosed pricing and self-reported accuracy.
Integrations
- Microsoft Excel
- API
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