AssemblyVersion

AssemblyVersion is a version identifier assigned to a .NET assembly that forms part of the assembly’s identity. The runtime uses this version during binding to locate and load the correct assembly, making it a key factor in compatibility and deployment. A typical AssemblyVersion follows a four-part format: major.minor.build.revision. The common intent is that changes to the major or minor parts signal breaking or significant changes, while build and revision can reflect smaller updates. Some toolchains historically allowed a wildcard in the build or revision components (for example, 1.0.*) to auto-increment, but this is not universally supported and can complicate binding in modern environments.

AssemblyVersion differs from AssemblyFileVersion and AssemblyInformationalVersion. AssemblyVersion is used by the runtime for binding and identity. AssemblyFileVersion is a Windows file metadata value shown in file properties and has no impact on binding. AssemblyInformationalVersion is a string for informational purposes, often including pre-release or build metadata. Because AssemblyVersion affects binding, changing it can require dependent projects to update their references or rely on binding redirects to preserve compatibility.

Specification and placement: in older projects, AssemblyVersion is declared in AssemblyInfo.cs with an attribute such as [assembly: AssemblyVersion("1.2.3.4")]. In SDK-style projects, version values are typically defined in the project file using elements like <Version>, <AssemblyVersion>, and <FileVersion>, allowing explicit control over each artifact.

Best practices emphasize stable major/minor versions for public APIs and careful management of binding to avoid breaking consumers. Changing the AssemblyVersion is a signaling mechanism for compatibility, and accompanying binding policies should be planned accordingly.