Microsoft .NET 9 EOL November 10, 2026

What End of Life Means for .NET 9

Microsoft .NET 9 reached end of life (EOL) on November 10, 2026, ending both active support and security patch delivery. Because this was not a long-term support (LTS) release, it never received the extended support period that LTS versions do. The final version in the 9.x line is 9.0.21.

At EOL, the following stops from Microsoft:

• Security patches: No new CVEs will be addressed for .NET 9 runtime, libraries, or tooling.
• Bug fixes: Non-security defects will not be backported.
• Technical support: Chat, phone, or Premier support cases for .NET 9 will not be accepted.
• Azure compatibility: Microsoft may introduce breaking changes to Azure services that require .NET 10 or later.

What Still Works on .NET 9 After EOL

Your existing .NET 9 binaries, applications, and SDK will continue to run. The CLR and JIT are stable and do not phone home. You can:

• Run production workloads on Windows, Linux, or macOS.
• Use NuGet packages that target .NET 9 or lower, provided they don't receive security updates of their own.
• Deploy to on-premises servers, VMs, or containers (subject to host OS support).

What breaks eventually:

• Patch dependency chains: NuGet packages that become unsafe because their own dependencies stop patching.
• Compliance mandates: PCI DSS, HIPAA, SOC 2, and other audits require patching of critical and high-severity CVEs.
• Future OS updates: Windows Server 2025 and later may remove .NET 9 runtime components.

Who Legitimately Stays on .NET 9

Some organizations remain on .NET 9 for sound operational reasons:

• Locked application dependencies: A third-party library or internal component requires .NET 9-specific APIs or runtime behavior.
• Certified environments: Medical devices, industrial controllers, or embedded systems where re-certification with .NET 10 is expensive or impossible.
• Hardware constraints: Thin clients, ARM32 devices, or older single-board computers that lack .NET 10 support.
• Budget-freeze cycles: Short gaps between planned migration windows.

These teams often run .NET 9 behind a reverse proxy or inside an isolated VLAN to reduce exposure.

Real Security and Operational Risks

Running .NET 9 without support exposes you to:

• Unpatched remote code execution (RCE) CVEs: .NET Core has a history of critical RCEs — those discovered in 2027 or later will not be fixed by Microsoft.
• Broken supply-chain tooling: The .NET SDK for 9 may stop resolving NuGet package metadata correctly.
• No SLA for regression fixes: If a .NET 10 update breaks something in your runtime, you have no recourse with Microsoft.
• Auditor pushback: Many regulatory frameworks require active vendor support for production runtime components.

Third-Party Support Options for .NET 9

Third-party support for .NET 9 provides a bridge while you plan your migration. Providers like 3rd Party Support backport critical security patches and offer technical support for the runtime, SDK, and deployment tooling — typically at 40–70% less than the last Microsoft renewal.

What you get:

• Custom patches for .NET 9-specific CVEs that Microsoft leaves unaddressed.
• Hotfixes for runtime crashes or threading issues that block production.
• SLA-based escalation (often 4-hour response) from engineers who know the .NET Core internals.
• Compatibility guidance for running .NET 9 alongside .NET 10 in mixed environments.

Next Steps

If your organization still runs .NET 9, start by inventorying all application dependencies and runtime versions. For workloads that cannot migrate immediately, contact us to discuss a tailored support plan that keeps your applications secure and compliant.

---

Lifecycle data sourced from endoflife.date/dotnet. Microsoft .NET 9 reached EOL on November 10, 2026.