K1x vs Additive: K-1 and K-3 Automation Software Comparison

Tax teams don’t need another “maybe next season” tool; they need hours back this season. Between late K-1s, sprawling K-3 footnotes, and state schedules, the cost of manual handling is real: delays, rekeying errors, and frazzled reviewers. Two names keep coming up to fix that: K1x and Additive. Below is a practical, paragraph-style comparison to help you decide what fits your workflow, stack, and risk profile.

What problem are we actually solving with K-1/K-3 automation?

Both vendors read complex K-1/K-3 packets (including state attachments and footnotes), standardize the data, and push structured outputs into your downstream tax systems. The goal is straightforward: to compress cycle time, reduce manual touches, and enhance the consistency of workpapers and filings.

How do K1x and additive approaches handle data extraction and accuracy?

K1x’s K1 Aggregator® leans on patented AI to read face pages, white-paper footnotes, K-3 foreign reporting, and state K-1s, with claims like 11.8-second extraction and ~90% manual reduction, contributing to a promoted 66% cycle-time cut and an independently assessed 287% ROI (per the vendor’s referenced analysis). Additive positions its gen-AI engine around speed at scale, processing packages with tens of thousands of pages, and emphasizes accuracy claims of over 99% on characters of income and over 95% on footnotes, including complex tables. In practice, firms should test on their own messy edge cases to see which model handles their specific statement styles best.

Which forms and jurisdictions are covered?

K1x covers K-1/K-3 and state data broadly and, with Aggregator Plus, now extracts 1099s (and newly W-2s) to consolidate intake. During production, K1 Creator generates K-1/K-2/K-3 and investor packages, and supports 42 state taxing jurisdictions for K-1/990 workflows (the company sometimes counts “47 state & federal jurisdictions” using a different convention). Additive lists federal K-1 variants (Form 1065, 8865, 1041, 1120-S), K-3, 199A, 926, 8621, UBTI, and 65 state forms—a draw if you handle a broad, multi-state footprint.

What does the review and workpaper experience look like?

K1x delivers allocation grids, validation checks, and a digital investor package (PDF plus a “.k1x” Digital K-1 file) to streamline the review and exchange process. Additive is unapologetically Excel-centric: upload via web or Excel Add-in, review inside spreadsheets, then export clean workpapers to Excel/JSON/PDF. If your reviewers live in Excel and want to stitch workpapers right there, that UX can feel instant.

How do they integrate with downstream tax software and APIs?

K1x offers named, guided integrations into CCH Axcess, ProSystem fx, Thomson Reuters ONESOURCE, GoSystem Tax RS, and UltraTax CS, as well as an API/dev portal that exposes structured outputs (the Digital K-1 concept) for programmatic use. Additive markets an API and the Excel Add-in, with a “send to your tax software” positioning. Following its acquisition by Thomson Reuters (Sept 2025), you can expect tighter TR ecosystem alignment over time, which is good news for ONESOURCE/UltraTax shops evaluating K-1 ingestion at scale.

Where do the platforms differ beyond ingestion?

K1x frames a complete RECEIVE → PRODUCE → EXCHANGE workspace: AI intake and validation, wizard-driven K-1/K-2/K-3 production with a universal footnote library, investor package assembly, and even tax-exempt filing with 990 Tracker® (IRS-approved e-file for 990 families) plus state support. Additive focuses on ingestion → workpapers → export, keeping your prep inside Excel and your filings in your existing tax suite, which is lean, fast, and friendly to established firm processes.

What about security, compliance, and data use?

Both vendors advertise SOC 2 Type II. K1x runs a public Trust Center detailing product security (encryption at rest, audit logging, SDLC, AI transparency, subprocessors). Additive states encryption at rest and TLS 1.2+ in transit, regular pen-testing, SSO+MFA, and a policy allowing creation of de-identified “Derivative Information” for internal model/product improvements, with client-owned content and deletion upon request (within 30 business days). If data governance is tight at your firm, get these artifacts and data-use specifics under NDA.

Who is using each, and what signals should I weigh?

K1x markets adoption across 40,000+ organizations, with a presence in 20 of the Top 25 accounting firms and deep traction among institutional investors and tax-exempt filers. Recent expansions include 1099 and W-2 extraction. Additive cites use by Top 20 accounting firms, public testimonials from large practices, and a strategic relationship with RSM US (as of November 2024), followed by the Thomson Reuters acquisition, which serves as a strong distribution signal for TR firms.

How do pricing and ROI compare?

Neither vendor publishes price cards; instead, both typically price by volume, product, and integration. K1x highlights ROI (e.g., 287%) and cycle-time reductions; Additive emphasizes accuracy and time savings in workpaper creation. Your best bet is a time-boxed pilot using a representative sample (including your ugliest footnotes) and comparing hours saved, reviewer rework, and import friction into your tax suite.

So which one is right for your firm?

Suppose you want an end-to-end tax workspace that not only ingests but also produces K-1/K-2/K-3 packages, exchanges data digitally with investors, and integrates with 990 e-filing. In that case, K1x aligns with that operating model and plugs into both Wolters Kluwer and Thomson Reuters suites. If your reviewers work in Excel, you want to work with workpapers quickly, and you’re a TR-standardized practice expecting deeper native ingestion inside ONESOURCE/UltraTax, Additive is compelling, especially after the acquisition. Many firms will trial both: run the same packet set, measure prep/review time, validate mapping into your tax software, and press each vendor on security artifacts, API scope, state coverage edge cases, and support SLAs.

Conclusion

K-1//K-3 automation isn’t a nice-to-have anymore; it’s how you hit deadlines without ballooning staff hours. K1x offers a broad, patented platform that automates intake, production, and exchange with pre-integrated solutions across various ecosystems. Additive brings Excel-first workpapers, impressive accuracy claims on footnotes, and now the reach of Thomson Reuters. Choose the one that best matches your reviewers’ habits, your software stack, and your multi-state and exempt footprint, and let a short, evidence-driven pilot decide for you.

Contact Genwise today to get expert advice tailored to your business and confidently move forward with the right platform.