Support for .NET 8 and .NET 9 to End in November, Microsoft Warns

Microsoft announced on July 16 that support for its software frameworks ”.NET 8” and ”.NET 9” will end on November 10, 2026. According to a report by Publickey’s jniino, applications developed using these versions will continue to function after the support period ends. However, no new patches will be provided for bugs or vulnerabilities discovered after this date.

.NET 8, released in November 2023 as a Long-Term Support (LTS) version, was designed with a three-year support period. On the other hand, .NET 9, launched in November 2024 as a Standard Term Support (STS) version, has a two-year support cycle. Both versions will reach the end of their respective support periods this November.

.NET 10 Recommended as Migration Target

To continue receiving security updates and bug fixes, developers must migrate to newer versions. As of November 2026, the supported versions will include .NET 10, released in November 2025, and .NET 11, set for release this November.

.NET follows a biennial release cycle for LTS versions, with .NET 10 being the designated LTS version in this cycle. Microsoft recommends .NET 10 as the primary migration target from .NET 8 or .NET 9. LTS versions are considered ideal for enterprise environments due to their guaranteed long-term stability and support.

.NET 11, expected to launch as an STS version, will not offer the extended support period of LTS versions. This distinction should be factored into migration planning.

Impact of End of Support

Applications developed on unsupported versions will not cease to function. However, if security vulnerabilities are discovered, no patches will be provided, increasing the overall risk to the system. This is particularly concerning for web applications exposed to external networks or backend systems handling sensitive data, where vulnerabilities could be exploited.

Additionally, libraries and packages dependent on older runtime versions may cease updates for compatibility. This not only limits access to new features and performance improvements but also raises the security risks associated with third-party components.

IT departments and development teams must calculate the time remaining until the end of support and urgently formulate migration plans. In large-scale systems, migration efforts—such as verifying codebase compatibility, updating libraries, and testing in controlled environments—may take several months to complete.

Key Considerations for Migration

Migrating from .NET 8 or .NET 9 to .NET 10 requires careful review of API compatibility and operational changes. Microsoft provides compatibility guides in its official documentation, allowing developers to preemptively identify breaking changes.

Special attention should be given to systems built on .NET 8, as it is an LTS version widely used in enterprise applications. For these systems, verifying that dependent third-party libraries are compatible with .NET 10 is crucial.

Furthermore, developers must also confirm the compatibility of the entire development environment, including Visual Studio and CI/CD pipelines. Updates to build tools and testing frameworks may be necessary due to changes in target frameworks.

Comparison with Past Support Policies

Since .NET Core, Microsoft has adopted a regular release cycle and clear support policies. LTS versions have a three-year support period, while STS versions are supported for 18 to 24 months. This approach enables developers to plan version upgrades systematically, although it shortens the migration cycles compared to the .NET Framework era.

In the .NET Framework 4.x series, extended support was provided over a much longer period, while .NET (formerly .NET Core) enforces stricter timelines. Organizations must recognize this shift and establish systematic processes for regular upgrades.

Editorial Opinion

Although this end-of-support announcement is a routine update, the limited four-month grace period for migration is noteworthy. Particularly for users of .NET 8 (an LTS version), migration planning should align with the cycle of transitioning to the next LTS version during the support period. Migration to .NET 10 is advised not only for security reasons but also to take advantage of performance improvements and new features.

From a long-term perspective, the standardization of Microsoft’s release cycle may influence corporate technology strategies and workforce development. A hybrid approach—using LTS versions as a foundation while experimenting with STS versions—might be a viable strategy. Additionally, as cloud-native adoption grows, automating runtime updates could become a competitive advantage.

The editorial team believes that the importance of tools and community-driven knowledge-sharing to ease migration burdens is increasingly evident. For complex large-scale systems, migration may require not just version upgrades but also a fundamental redesign, highlighting a broader industry-wide discussion on software sustainability.

References

• ”.NET 8と.NET 9は今年の11月でサポート終了、マイクロソフトが警告”, by jniino — Publickey, 2026-07-16T18:30:28.000Z (ARR)
• Source URL: https://www.publickey1.jp/blog/26/net_8net_911.html