.NET 9 Performance Improvements Summary

With every release, .NET becomes faster & faster! You get these improvements for free by just updating your project to the latest .NET!

It’s very interesting that 20% of these improvements are implemented by open-source volunteers rather than Microsoft employees. These improvements mostly focus on cloud-native and high-throughput applications. I’ll briefly list them below.

1. Dynamic PGO with JIT Compiler

• What is dynamic PGO?

  With “Profile Guided Optimization” the compiler optimizes the code, based on the flow and the way the code executes. It is predicated on the idea that every potential behavior of the code will always transpire.

• What’s Improved?

  The tiered compilation, inlining, and dynamic PGO are three ways that .NET 9 optimizes the JIT compiler. This enhances runtime performance and speeds up the time for apps to launch.

• Performance Gains

  CPU use is lower during execution; therefore, startup times are about 15% faster.

• As a Developer

  Faster, smoother deployments with reduced warm-up times... These enhancements reduce latency for applications with complex workflows, particularly in microservices and high-throughput environments.

• How to activate Dynamic PGO?

  Add the following to your csproj file, or if you have several csproj files, you can add it once in Directory.Build.props file. Check out this link to understand PGO.

  <PropertyGroup>
    <TieredPGO>true</TieredPGO>
  </PropertyGroup>

2. Library Improvements

• What’s Improved?

  LINQ and JSON serialization, collections and libraries are significantly improved with .NET 9.

• Performance Gains

  JSON serialization performance increases by about 35%. This helps with heavy data parsing and API requests. Less memory is allocated to Span operations as well, and LINQ techniques such as Where and Select are now faster.

• As a Developer

  This means that apps will be faster, especially those that handle data primarily in JSON or manipulate data with LINQ.

3. ASP.NET Core

• What’s Improved?

  Kestrel server has undergone significant modifications, mostly in processing the HTTP/2 and HTTP/3 protocols.

• Performance Gains

  Now, Kestrel handles requests up to 20% faster and has a 25% reduction in average latency. Improved connection management and SSL processing also result in overall efficiency gains.

• As a Developer

  These modifications result in less resource use, quicker response times for web applications, and more seamless scaling in high-traffic situations.

4. Garbage Collection & Memory Management

• What’s Improved?

  NET 9’s garbage collection (GC) is more effective, especially for apps with high allocation rates.

• Performance Gains

  Applications experience smoother garbage collection cycles with 8–12% less memory overhead, which lowers latency and delays.

• As a Developer

  The performance will be more reliable and predictable for developers as there will be fewer memory-related bottlenecks, particularly in applications that involve frequent object allocations.

5. Native AOT Compilation

• What’s Improved?

  Native AOT (Ahead-of-Time) compilation is now more efficient by lowering memory footprint and cold-start times. This leads to better support for cloud-native applications.

• Performance Gains

  Native AOT apps now have faster cold launches and use 30–40% less memory. This improvement focuses on containerized applications.

References:

• Microsoft .NET blog post.
• What’s new in the .NET 9 runtime?