"Our frontline staff mentioned that Microsoft seems to be warning about an approaching deadline for our business system, but to be honest, I have no idea what it means." We received this consultation from the president of a parts trading company with about 30 employees. The internal order processing and inventory management system reportedly runs on something called ".NET," and they heard support was ending. However, they did not know how serious this was for their business, or whom to ask and what questions to pose. With their former IT lead having resigned, having no internal staff capable of making technical judgments is a very common situation.
This is not someone else's problem: support for .NET 8 and .NET 9 ends on November 10, 2026. Across Japanese SMBs, many business systems, internal tools, and web applications run on .NET, and a substantial number will likely hit the deadline unnoticed. In this article, we explain how to identify if you are affected, how to check with vendors, and what decisions to make before November from the perspective of the commissioner—the party responsible for making business decisions and allocating budget. You do not need to understand technical details; you only need to grasp what is necessary to make informed decisions.
What Is Actually Ending
.NET is a software development and execution runtime provided by Microsoft. Acting as the foundation for business systems and web applications, it provides the environment on which applications run. This foundation has distinct versions, each with a predetermined support lifecycle.
Two versions are ending this time. .NET 8, released in November 2023 as an LTS (Long Term Support) release, launched with a committed three-year support window. .NET 9, released in November 2024 as an STS (Standard Term Support) release, had its support window extended to 24 months. These two versions reach their end of support together on November 10, 2026. The fact that one version is newer does not mean it is exempt, which often causes confusion.
What happens when support ends? Software updates, security patches, and technical support terminate. What matters most is the cessation of security patches. When new vulnerabilities are uncovered after the deadline, security patches will no longer be released. Consequently, you will be operating business systems on a foundation with known, unpatched security holes. Because systems will not immediately stop running, creating a sense of urgency can be difficult, but risks quietly compound as time passes.
Microsoft recommends upgrading to the next LTS release, .NET 10 (supported through November 2028). Migrating the underlying framework to this newer version is the primary recommended strategy.
How to Determine If Your Company Is Affected
The first thing to confirm is whether your system runs on .NET at all. This is often difficult to verify internally. As an initial check, see if any of the following apply to your organization:
- You outsourced custom business systems or internal tools several years ago
- You have internal systems running on Windows servers
- You recall hearing terms like ".NET," "C#," or "ASP.NET" from vendors in the past
- Frontline staff reported seeing notifications prompting for updates
If even one applies, your organization may be affected. However, not matching any does not mean you are safe. It is standard for SMBs to know neither the name nor the version of the underlying framework they run. That is precisely why you should not settle for internal guesswork; moving directly to the next step—asking your vendor—is the most reliable path.
The trading company president mentioned earlier was also unable to verify internally whether their system used .NET. Rather than trying to force a conclusion in-house at this stage, reaching out to the vendor assuming you do not know is the fastest and most accurate approach.
How to Inquire with Vendors and Contractors
If you have a vendor that built the system or handles ongoing maintenance, contacting them is the fastest path. However, asking vaguely, "Is our system okay?" risks receiving a dismissive "No problem," or conversely, provoking unnecessary anxiety and bloated proposals. Knowing what specific questions to ask as a client is essential for eliciting clear, objective answers. At a minimum, verify the following points in writing (such as via email) to preserve a record:
| Point to verify | Sample Specific Questions |
|---|---|
| Underlying framework and version | "Does our system run on .NET? If so, what version does it use?" |
| Applicability to the upcoming EOL | "Is our system affected by the .NET 8 or .NET 9 end of support on November 10, 2026?" |
| Risks and operational impact of inaction | "If no action is taken, what risks arise and which business operations will be affected?" |
If the vendor confirms your system is affected, follow up by requesting an estimate of required effort, the scope of impact, testing requirements, and an anticipated schedule. The goal here is not to demand an exact financial quote on the spot, but to gauge the general scale of the project. Because costs vary substantially by project, formal budgets will require an individualized estimate. If you are uncertain how to evaluate quotes or request competitive bids, our client's guide to successful outsourced system development outlines critical points to evaluate.
It is also common to encounter situations where you have lost contact with the original developer or maintenance contracts have lapsed. In such cases, you will need a third-party vendor to assess your system's current state, which ties directly into the broader question of how to sustain day-to-day operations. Reviewing our business system maintenance cost guide will provide a solid foundation for making these decisions.
What to Decide Before November
Once you confirm your system is affected, you must settle on a strategy before November 10. Doing nothing merely postpones the inevitable while accepting ongoing risk, leaving three practical options:
The first is migration (upgrade). This involves transitioning the foundation to an actively supported version like .NET 10. In most cases, this is the primary path forward. Upgrading from .NET 8 to .NET 10 is generally considered relatively smooth due to their close generational proximity. However, this is not an automated, hands-off task; thorough testing after the platform shift is mandatory to verify that all business functions continue operating without issue. Skipping this step leads to production bugs.
The second option is life extension. This involves deciding to continue operating the system as-is past the deadline when immediate migration is impossible due to specific constraints. However, this is synonymous with operating on an unpatched foundation and merely buys time while accepting lingering risk. For companies subject to customer security mandates or handling personal data, this creates severe compliance vulnerabilities, as discussed below. It should only be viewed as a temporary bridge to migration, accompanied by a firm target completion date.
The third is a complete rebuild. If the system is legacy software whose functionality no longer matches your current business operations, rebuilding it entirely represents a sound alternative. Extending the life of an inherently clumsy system merely through a framework upgrade is questionable as an investment. If prolonged use has degraded usability and alignment with current operations, weighing a simple technical upgrade against a full rebuild using insights from our guide on restoring usability in legacy business systems is highly recommended.
The core criteria are the remaining operational lifespan of the system and the severity of risks posed by inaction. If the system will be retired in a few years, an upgrade is sufficient; however, if it will serve as your operational backbone for years to come, strengthening your foundation now is well worth the investment.
The Inaction Risk: Failure to Protect Rather Than System Outages
Finally, let us review why this deadline cannot be taken lightly, framed from the perspective of system owners. Even when support ends, systems do not halt the next day. This is why decisions are frequently deferred under the rationalization that "it's still working fine." The true hazard, however, is not system downtime, but the loss of protection.
Once security updates stop, known vulnerabilities accumulate over time. Exploiting these flaws leads directly to leaks of customer and transaction data. Under the security control measures required by the revised Act on the Protection of Personal Information, continuing to run unsupported platforms may itself be deemed a failure to implement necessary safeguards. Clients and partners increasingly audit information security standards; operating mission-critical systems on unsupported foundations can become grounds for failing vendor qualification requirements.
In short, this is not merely an IT maintenance matter, but fundamental business risk management. With a firm deadline in November, do not stall on uncertainty over whether your company is affected. Finding out where you stand is where decision-making begins.
Consulting on Development and Migration
Unable to tell whether your system runs on .NET, or uncertain whether to migrate, extend, or rebuild if it does? This indicates a shortage of business decision-making inputs rather than a purely technical obstacle. At GleamHub, we assist system owners with assessing existing business systems, checking .NET versions, and evaluating migration paths versus full rebuilds. We do not push predefined solutions; we work candidly alongside you to identify the optimal balance of risk and cost for your company. Engagements are quoted on an individual project basis. You are welcome to start simply by asking, "Are we affected?" via our contact page. Let us take the first step together to determine your strategy ahead of November.
