Skip to content
House of Business
Call us

.NET 8 and 9 lose support on 10 November, on the same day

Two .NET versions out of support on one day does not happen often. What it means for portals and integrations running on them. And what to ask this month.

By Marco

On 10 November 2026 Microsoft ends support for .NET 8 and .NET 9 on the same day. That is two months from now. For anyone running software on either version, this is the moment to ask about the plan.

Why two versions at once

.NET 8 is the LTS version that many portals and integrations have been built on over the past three years. LTS stands for long-term support: three years of updates. .NET 9 is the interim version that appeared a year later, with two years of support. Because of that difference in duration, both now expire on the same day.

The successor is .NET 10, again an LTS version, supported until November 2028. .NET 11 has been available since 8 September as a release candidate with a go-live licence, but that is an interim version again. For business software that has to last for years, .NET 10 is the logical choice.

What changes after 10 November

This month the September updates came out with eight security fixes for .NET 8, 9 and 10. After 10 November, 8 and 9 no longer get those. The software keeps working, but a vulnerability found after that date is no longer fixed in those versions. For a portal exposed to the internet or an integration that handles customer data, that is not a situation to stay in for long.

What this means for our customers

If your portal or integration runs with us on .NET 8 or 9, the upgrade to .NET 10 is in the maintenance planning for October or has already been done. You do not need to do anything for it.

  • The upgrade from 8 to 10 is usually a day's work per application, including testing on the acceptance environment. From 9 to 10 it is less.
  • The cost falls within the support contract. This is the kind of work maintenance is meant for.
  • After the upgrade the application runs on a version that receives updates until November 2028.

Software with another party

If you have software running on .NET 8 with another supplier, ask about their plan this month. Three questions are enough: which version does it run on now, when does it move to .NET 10 and is that covered by the maintenance contract. If there is no clear answer, that says something about how the maintenance is organised.

Sources

.NET support policy: dotnet.microsoft.com/platform/support/policy/dotnet-core. September updates: devblogs.microsoft.com/dotnet, servicing updates September 2026.

This text first appeared as a post on LinkedIn

More articles

All articles
Marco

My AI assistant and her colleagues

Since September my AI assistant has been working with colleagues that each have a single craft. Every colleague has its own permissions and a measurable standard. Miss that standard three times and you are out. On the reason for that strictness and the counterargument.

Read the article
Six white humanoid robots in a dark blue studio. Front right, a female robot with blue light lines looking into the camera, behind her five robots out of focus in a row. On the left the Dutch text 'Mijn AI-assistent heeft er sinds deze maand collega's bij', bottom right the House of Business mark.
Marco

Support is the foundation of the partnership, not an afterthought to the project

A proposal usually covers the build. At HOB, support is part of that same first conversation: its own contract with an SLA for updates to packages, the framework and security. What that means in practice, and what to ask any software partner.

Read the article

Curious what this means for your business?

A first conversation. You tell us where it hurts, we tell you how we would approach it.

Book an intro callor call +31 (0)73 234 02 30