In a blog post published on the .NET Blog on September 15, 2026, Microsoft reviews hundreds of improvements that arrived in .NET 11, presenting them as the cumulative result of extensive work on the just-in-time JIT compiler, the runtime, and libraries. The core idea is not that there is a single feature that doubles performance, but that small, recurring gains are being removed: a bounds check that is no longer necessary, a memory allocation that has been eliminated, a lock or system call that has been avoided, and loops that now execute with fewer processor cycles.
The importance of this type of optimization is that much of it does not require modifying or redesigning application code. The JIT compiler converts the IL intermediate language usually produced by C#, F#, and Visual Basic into native instructions executed by the processor. When it can prove that a virtual call can be directed to a specific type, or that a given check cannot fail, it can produce shorter instructions and improve the chances of inlining functions into one another.
Improving the Removal of Abstractions
A prominent part of the material focuses on what Microsoft calls the removal of abstractions, meaning enabling the runtime to bypass the execution cost of some abstractions that developers need in software design. Examples include interface calls and virtual methods, where traditional execution may need to load multiple pointers and perform an indirect call, preventing the called function from being inlined into the current function.
.NET 11 continues to develop the “Guarded Devirtualization” approach. The JIT identifies the most common type during execution, creates a fast path to call it directly, and retains the virtual path to ensure correct execution if a different type appears later. When this enables function inlining, other optimizations become possible, such as constant propagation, branch elimination, and bounds-check removal.
The work extends to generic virtual methods, ReadyToRun and NativeAOT operations, and default virtual implementations in interfaces. The material notes that these improvements may increase code size when direct calls lead to more inlining, but they make the program’s logic more visible to the optimizer.
Fewer Allocations and Less Impact on the Garbage Collector
.NET 11 also continues expanding Escape Analysis, which attempts to determine whether an object created inside a function escapes its scope. If it is proven not to leave that scope, the JIT can avoid placing it on the managed heap, or eliminate the allocation entirely in some cases, reducing pressure on the garbage collector.
The source presents examples of improved nullable boxing and conditional escape analysis for collection enumeration. In one measurement, a 32-byte allocation disappeared when enumerating a collection built from an instance field, and execution time fell from 13.874 nanoseconds in .NET 10 to 2.674 nanoseconds in .NET 11. Some cases using generic values or interface calls can also now avoid temporary allocations of 24 bytes.
These figures concern extremely small operations, so they should not be interpreted as a fixed, general increase in the performance of every application. Their primary value is revealing code patterns that the runtime can optimize, while the actual impact will depend on the application’s nature and its hot paths.
Delegates and the Asynchronous Runtime
.NET 11 includes changes to delegate representation in CoreCLR, including the removal of a field the size of one pointer from every delegate object in a 64-bit process, meaning a saving of 8 bytes per delegate according to the material. Delegate representation fields were also rearranged in NativeAOT, and some values used together were placed near one another in memory to improve access on architectures such as Arm64.
The blog post also introduces a new architecture under the name “runtime async,” which transfers part of the responsibility for transforming async/await methods from the C# compiler to the JIT and runtime. In the traditional model, the compiler creates a state machine containing the fields needed for resumption, such as parameters, local values, awaiters, and execution state. The new model instead relies on a smaller contract in IL, leaving the runtime and JIT to make decisions related to what remains alive at suspension points, how continuation objects are laid out, and how the externally visible Task or ValueTask is created.
What Changes in Practice?
The editorial takeaway from this round is that .NET 11 is betting on improving existing code as much as on adding new APIs. Applications that rely heavily on interfaces, generic methods, delegates, enumeration, and asynchronous operations may benefit without direct source changes, but the extent of the improvement will vary according to the processor, operating system, runtime settings, and workload characteristics.
Microsoft recommends testing the results with BenchmarkDotNet, installing .NET 10 and .NET 11 and running the same code on both versions. It cautions that the published measurements are extremely precise tests and may be affected by hardware, other processes, and environment settings. Therefore, the results of a microbenchmark alone are insufficient to make an upgrade decision or demonstrate an overall improvement; actual application workloads must be measured before adopting broader conclusions.