AnyCPU

AnyCPU is a .NET platform target used for assemblies, indicating that the code is architecture-agnostic and can run on both x86 and x64 environments. When a program or library is built as AnyCPU, the runtime is responsible for loading it in a way that matches the host process architecture.

On Windows, an AnyCPU executable will run as a 32-bit process on 32-bit Windows. On 64-bit Windows, the runtime typically starts a 64-bit process by default, unless an application manifest specifies otherwise. This behavior can be controlled by a manifest flag called Prefer32Bit, which, when set to true, forces the executable to run as 32-bit on 64-bit Windows. Libraries built as AnyCPU do not independently set their process architecture; they adapt to the host process where they are loaded.

The practical implication of AnyCPU depends on dependencies. If an application relies on native libraries that are architecture-specific, you must provide matching 32-bit and 64-bit native binaries or use a loading strategy that selects the appropriate one. Otherwise, loading a 64-bit native library into a 32-bit process (or vice versa) will fail.

In the modern .NET landscape, the relevance of AnyCPU varies by platform. .NET Framework projects commonly use AnyCPU, while .NET Core and later versions emphasize runtime identifiers and architecture-specific publishing. For these runtimes, architecture is often determined by the published target (RID) or by the runtime, rather than a simple assembly target, and developers may publish separate builds for x86 and x64 as needed.