.NET Conf Local - .NET 10 Breaking Changes

Presentation for the Dot Net North '.NET Conf Local' event in January 2026. An overview of .NET 10 Breaking Changes.

Talk Description:

A look through the different Technology Areas of .NET 10 Breaking changes, and the different types of change: Behavioural changes, source incompatibilities and Binary incompatibilities.

Covering a selection of changes in ASP.NET Core, Containers, Core .NET libraries, Cryptography, Extensions, Globalization, Networking, SDK and MSBuild, Serialization and WPF.

Includes a mention of upgrading to Visual Studio 2026.

Event Meetup Listing • Presentation Link

Links from presentation

🎓 Breaking changes in .NET 10 - Microsoft Learn

ASP.NET Core

• Cookie login redirects are disabled for known API endpoints
• Deprecation of WithOpenApi extension method
• Razor runtime compilation is obsolete

Containers

• Default .NET images use Ubuntu

Core .NET Libraries

• Consistent shift behavior in generic math
• Specifying explicit struct Size disallowed with InlineArray
• System.Linq.AsyncEnumerable in .NET 10

Cryptography

• Environment variable renamed to DOTNET_OPENSSL_VERSION_OVERRIDE
• .NET 10 requires OpenSSL 1.1.1 or later on Unix

Extensions

• Message no longer duplicated in Console log output

Globalization

• Environment variable renamed to DOTNET_ICU_VERSION_OVERRIDE

Networking

• Uri length limits removed

SDK and MSBuild

• dotnet new sln defaults to SLNX file format
• project.json no longer supported in dotnet restore
• PackageReference without a version will raise an error

Serialization

• XmlSerializer no longer ignores properties marked with ObsoleteAttribute

WPF

• Empty ColumnDefinitions and RowDefinitions are disallowed

🚀 Get .NET 10

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