What is KSK2? How the NTA's new system, going live this month, changes tax audits
In September 2026, Japan's National Tax Agency (NTA) replaces its core computer system for the first time in roughly 25 years. The new system is called KSK2, the next-generation Kokuzei Sogo Kanri (comprehensive tax administration) system. Headlines proclaiming that "AI is taking over tax audits" are flying around, but what actually changes, and what does not? Based on primary sources, this article sorts out what sole proprietors, corporations, and salaried workers with side income should keep in mind in practice.
• KSK2 is the NTA's new core system, going live in stages from around September 2026.
• The biggest change is that paper gets digitized too and everything is linked — paper returns are read by AI-OCR and cross-checked across tax categories.
• It is not a system where "AI audits you automatically". But audit targets will be selected more precisely.
• The right response is the same as ever — accurate bookkeeping and filing by the deadline. Only the risk of non-filing and partial reporting of sales goes up.
From KSK to KSK2 — what changes
The current KSK (Kokuzei Sogo Kanri, comprehensive tax administration) system was designed in the 1990s and rolled out nationwide in 2001. A quarter century on, the NTA has rebuilt it as KSK2, the centerpiece of its "digital transformation of tax administration" program[NTA Tax Administration DX].
| Aspect | Current KSK | KSK2 |
|---|---|---|
| Data intake | Paper returns only partly digitized, after manual data entry | Paper returns are scanned and fully digitized by AI-OCR (put on the same footing as e-Tax) |
| Data structure | Managed separately by tax category (income tax, corporate tax, consumption tax...) | Data-centric design that can be referenced and cross-checked across tax categories |
| Infrastructure | Mainframes running a proprietary OS | Full migration to a general-purpose platform. Easier for examiners to access from the field |
| Analytics | Veteran examiners' rules of thumb plus limited data analysis | More sophisticated selection of audit targets through analysis of accumulated data (AI and statistical analysis) |
In one sentence: the old premises — "paper is hard to see" and "different tax categories are not linked" — disappear. Statutory records such as withholding slips and payment records, invoice-issuer registration data, past filing history — information that was already flowing into the tax office will now be connected faster and more widely than before.
"AI will do the tax audits" is a misunderstanding — but the selection net gets finer
Media and social posts have run ahead with phrases like "AI tax audits are starting", but KSK2 itself is not a system that conducts audits automatically. Whether to open an audit, and whether to assess additional tax, remains a decision made by human examiners, as before.
That said, the NTA has long published its policy of using data analysis to identify taxpayers likely to have under-reported and to select audit targets, and KSK2 is the foundation for it[NTA Tax Administration DX]. In fact, even with the number of tax audits roughly flat, the additional tax assessed per case has been rising year after year — the shift from "wide and shallow" to "deep where it looks suspicious" is already visible in the data.
Stronger data matching mainly exposes: (1) non-filing (your clients' payment records and invoice data suggest sales exist, yet no return was filed); (2) partial reporting (declaring only part of your sales); (3) contradictions across tax categories (sales figures that do not match between consumption tax and income tax, for example). For what examiners actually probe, see our Tax Audit Files series based on published tribunal decisions and The Reality of Tax Audits.
Will the data be protected? The reality of "access from the field" and the real risk
Reading this far, an obvious question arises: "If examiners can access the system from the field, is the data safe from leaks?" First, the facts. According to press reports, KSK2 terminals are designed to be used over the closed government network (GSS network) shared across ministries, and are not directly exposed to the internet[Nikkei xTECH]. This is not a setup where the data sits somewhere anyone outside can attack.
Even so, there are two reasons not to treat the risk as zero.
- Actual leaks have happened through insiders, not external hacking — in August 2026, an examiner at the Osaka Regional Taxation Bureau was manipulated by a scam call impersonating the police and sent information on 259 taxpayers to an outside party via LINE. You do not need to break the system if you can deceive a person. And advances in AI are making precisely this "deceiver's" playbook more sophisticated (see misconduct by tax officials and how taxpayers can protect themselves).
- Centralization is a double-edged sword — the more data is linked across tax categories, the more efficient administration becomes, but for the same reason the scope of what leaks grows larger when a breach happens. What would once have been confined to a single tax category in the decentralized era now comes out bundled per taxpayer.
Tax officials are bound by a double confidentiality obligation heavier than that of ordinary civil servants, backed by criminal penalties, and technical defenses such as the closed network and access controls are of course in place. Still, since this once-in-25-years overhaul raises the concentration of data, the NTA owes taxpayers more accountability than ever for how access-log auditing and least-privilege controls will actually be operated — that is the demand worth putting on record from the taxpayer's side. What we ourselves can do in self-defense (such as spotting scam calls impersonating the tax office) is summarized in this article.
What it means in practice, position by position
- Sole proprietors and freelancers — "file on paper and stay under the radar" is now completely a thing of the past. Unrecorded sales are more likely to be caught against your clients' statutory records and invoice data, so accurate bookkeeping and invoice management are themselves your defense (see the basics of blue-return filing).
- Salaried workers with side income — through payment records and platform reporting, side income is on the easily-visible side. Including the common misreading of the 200,000-yen rule, check our guide to tax returns for side jobs.
- Corporations — cross-category matching (corporate tax, consumption tax, withheld income tax) becomes more efficient, so consistency checks between financial statements and consumption tax returns matter more.
- People with unfiled past years — there is no need to panic around the system switchover, but the expected value of doing nothing keeps falling. A voluntary late return filed before an audit finds you carries lighter penalty taxes (see coming back from non-filing).
Finer matching also means innocent transcription errors and timing differences in recognizing income become easier to spot. Moving from handwritten or spreadsheet management to accounting software plus e-filing reduces this class of mistakes at the source. As the collecting side gets more efficient, defending yourself with systems, not effort, is the rational move.
What to do today
- Check that this year's books of sales and expenses are up to date (if you are behind, catch up within the week)
- Settle on a single rule for keeping invoices and receipts (paper in monthly envelopes, data in sorted folders)
- If any past year may be unfiled or under-reported, review the steps for voluntary filing
Frequently asked questions
When does KSK2 start operating?
It goes live in stages from around September 2026. Nothing happens the instant it switches over; digitization of paper returns and the use of analytics will spread step by step.
Will AI conduct tax audits automatically?
No. KSK2 is a platform for data management and analysis; the decision to audit and the audit itself remain in the hands of human examiners. However, data-driven selection of audit targets will become more sophisticated, so non-filing and inconsistencies in returns are more likely to be found.
Do sole proprietors need to do any paperwork for this?
No procedures are required of taxpayers for KSK2. What you should do is unchanged: keep accurate books and file by the deadline. If anything, since even paper returns will be fully digitized, switching to accounting software and e-Tax reduces both mistakes and workload.
Should I worry about data leaks with KSK2?
The terminals are designed to be used via a closed government network, not connected directly to the internet. However, in August 2026 an official was manipulated by a scam call and sent information on 259 taxpayers to an outside party — a case that actually happened. The realistic leak path is attacks targeting insiders rather than external hacking. Since centralized data enlarges the impact of any breach, how operations and accountability are strengthened deserves close watching.
Sources
This article is based on the following published materials and commentary. The launch timing and details of the system's features may change with future NTA announcements.
- National Tax Agency: Digital transformation of tax administration (Tax Administration DX)
- National Tax Agency: Press releases and published audit statistics
- Miroku Jyoho Service: KSK2 feature (private-sector commentary)
*This article is general information, not individual tax advice. How to handle an audit and whether past-year filings are needed depend on your situation. Consult the tax office or a licensed tax accountant for specific decisions.
