As November rolls around, so does Microsoft’s newest release of .NET. As always, it brings a range of changes and updates. this time with a focus on cloud-native development, AI integration, and performance improvements.

Microsoft has listed the changes to expect in their official release announcement, but just as I did with .NET 6 and .NET 8, I’m back again to give you the low-down on what you’ll need to know, especially if you’re thinking of migrating from an earlier version.

In this article we’ll look at .NET 9’s “Standard Term Support” and what that means for you. We’ll of course cover what’s new in this version, as well as what’s deprecated. Finally we’ll talk about what you’ll need to take on board if you’re planning to migrate over to .NET 9.

Standard Term Support for .NET 9

.NET 9 is an “odd numbered release”. This means that it’s going to be “Standard Term Support” (STS), unlike it’s Long Term Support (LTS) predecessor, .NET 8.

Starting with .NET 5, Microsoft switched up their release pattern. Now, odd-numbered versions are considered Short-Term Support (STS) with 18 months of support, while even-numbered ones are Long-Term Support (LTS), getting three years of support.

So what does this mean for .NET 9? As an STS release, .NET 9 will be supported until around May 2026. This is about six months before support for .NET 8 wraps up, which came out a whole year earlier! If you’re currently on .NET 8 and the new features of .NET 9 aren’t relevant to you, you may want to just skip the update entirely and wait for .NET 10 in 2025.

What’s new in .NET 9?

Microsoft’s list of changes and updates in .NET 9 might feel overwhelming at first glance, especially if you’re not heavily into .NET. But staying up to date is always important, so, I’ve gone ahead and broken down some of the key changes you’ll see come November.

More improvements in NuGet Package Security

When .NET 8 was released we talked about the improvements that came with it for auditing NuGet packages for vulnerabilities. In .NET 9 we’ll see even more developments on this.

NuGet auditing was added in .NET 8, and let you receive notifications about packages that might have security issues. Taking vulnerability scanning one step further, you can now scan for vulnerabilities in transitive dependencies. As with current audits, these warnings can be seen in both Visual Studio and on your build servers, giving you a good overview of package security in your development process.

It’s important to keep an eye on any vulnerabilities in your software, but not all of them are worth stressing over. Some can be serious and could affect the overall security of your application. Others might be labeled as potential threats but are harder to exploit.

Just ignoring these vulnerabilities or blindly upgrading isn’t exactly a great idea. For more information on vulnerabilities, check out our article What are NuGet Vulnerabilities and How to Manage Them

Quick Breakdown of Other Changes:

Aside from the NuGet audit improvements, the .NET 9 SDK will also introduce workload sets for version stability and better MSBuild integration. Other highlights include ML.NET 4.0’s new tokenizer support, .NET Aspire’s cloud-ready stack, and C# 13’s new syntax features like params collections and method group improvements.

.NET 9 will also deliver updates across the runtime and libraries. The runtime introduces a new feature switch model with trimming support and improved garbage collection. Libraries like System.Text.Json gain nullable reference type annotations, and LINQ adds new methods for data aggregation. Cryptography gets a one-shot hash method, and Reflection now includes the ability to save and debug emitted assemblies.

What’s Deprecated in .NET 9?

.NET 9 sees no additional deprecations since .NET 8, however, neither will we see any changes to currently deprecated .NET Framework technologies:

⚠ ASP.NET Webforms

⚠ Windows Communication Foundation

⚠ Windows Workflow Foundation

As we’ve covered in another article, ASP.NET Web Forms applications will remain functional, regardless of new .NET releases. On another note, WCF also continues to remain functional, thanks to being tied to .NET Framework’s support.

However this is no excuse to cling to any old technologies necessarily, there are more modern options you could go for. For example:

💡 Migrate Web Forms to Microservices

💡 Maintain them with a CI/CD pipeline

Migrating to .NET 9

Microsoft will always work to improve .NET; so, if you’re still working in .NET Framework or .NET Core, now is the time to start thinking about the future.

It’s a trivial matter if you’ve already upgraded to the “current” .NET series (.NET 5 to .NET 8). If you’re coming from Framework though, start preparing with these simple steps:

• Take an inventory of your existing applications.
• Identify if any of your applications are using deprecated libraries
• Plan out a rough schedule. As .NET Framework is tied to the operating system, there’s no immediate need to migrate
• Increase your release velocity – Rarely updating will only make migration more difficult over time.

Migrating can be scary. After all, it’s more than just an upgrade. If you’re thinking about making the jump, don’t forget to sign up for our free .NET 9 Migration guide today!