.NET 10 → .NET 11 Migration

Migrate a .NET 10 project or solution to .NET 11, systematically resolving all breaking changes. The outcome is a project targeting net11.0 that builds cleanly, passes tests, and accounts for every behavioral, source-incompatible, and binary-incompatible change introduced in .NET 11.

Note: .NET 11 is currently in preview. This skill covers breaking changes documented through Preview 3.

When to Use

• Upgrading TargetFramework from net10.0 to net11.0
• Resolving build errors or new warnings after updating the .NET 11 SDK
• Adapting to behavioral changes in .NET 11 runtime, ASP.NET Core 11, or EF Core 11
• Updating CI/CD pipelines, Dockerfiles, or deployment scripts for .NET 11
• Fixing C# 15 compiler breaking changes after SDK upgrade

When Not to Use

• The project already targets net11.0 and builds cleanly — migration is done
• Upgrading from .NET 9 or earlier — address the .NET 9→10 breaking changes first
• Migrating from .NET Framework — that is a separate, larger effort
• Greenfield projects that start on .NET 11 (no migration needed)

Inputs

Workflow

Answer directly from the loaded reference documents for information about .NET 11 breaking changes. You may inspect the local repository (project/solution files, source code, configuration, build/test scripts) as needed to determine which changes apply. Do not fetch web pages or other external sources for breaking change information — the loaded references are the authoritative source. Focus on identifying which breaking changes apply and providing concrete fixes.

Commit strategy: Commit at each logical boundary — after updating the TFM (Step 2), after resolving build errors (Step 3), after addressing behavioral changes (Step 4), and after updating infrastructure (Step 5). This keeps each commit focused and reviewable.

Step 1: Assess the project

1. Identify how the project is built and tested. Look for build scripts, .sln/.slnx files, or individual .csproj files.
2. Run dotnet --version to confirm the .NET 11 SDK is installed. If it is not, stop and inform the user.
3. Determine which technology areas the project uses by examining:
   • SDK attribute: Microsoft.NET.Sdk.Web → ASP.NET Core; Microsoft.NET.Sdk.WindowsDesktop with <UseWPF> or <UseWindowsForms> → WPF/WinForms
   • PackageReferences: Microsoft.EntityFrameworkCore.* → EF Core; Microsoft.EntityFrameworkCore.Cosmos → Cosmos DB provider
   • Dockerfile presence → Container changes relevant
   • Cryptography API usage → DSA on macOS affected; AIA cert download changes relevant
   • Compression API usage → DeflateStream/GZipStream/ZipArchive changes relevant
   • TAR API usage → Header checksum validation and HardLink entry changes relevant
   • NamedPipeClientStream usage with SafePipeHandle → SYSLIB0063 constructor obsoletion relevant
   • BackgroundService usage → Unhandled exceptions now stop the host
   • Microsoft.OpenApi direct usage → v3 API breaking changes in ASP.NET Core OpenAPI
   • EF Core SQL Server with Entra ID auth → SqlClient 7.0 auth dependency changes
   • NativeAOT native libraries on Unix → Output filename prefix changed
4. Record which reference documents are relevant (see the reference loading table in Step 3).
5. Do a clean build (dotnet build --no-incremental or delete bin/obj) on the current net10.0 target to establish a clean baseline. Record any pre-existing warnings.

Step 2: Update the Target Framework

1. In each .csproj (or Directory.Build.props if centralized), change:

   <TargetFramework>net10.0</TargetFramework>
   

   to:

   <TargetFramework>net11.0</TargetFramework>
   

   For multi-targeted projects, add net11.0 to <TargetFrameworks> or replace net10.0.

2. Update all Microsoft.Extensions.*, Microsoft.AspNetCore.*, Microsoft.EntityFrameworkCore.*, and other Microsoft package references to their 11.0.x versions. If using Central Package Management (Directory.Packages.props), update versions there.

3. Run dotnet restore. Fix any restore errors before continuing.

4. Run dotnet build. Capture all errors and warnings — these will be addressed in Step 3.

Step 3: Fix source-breaking and compilation changes

Load reference documents based on the project's technology areas:

Work through each build error systematically. Common patterns:

1. C# 15 Span collection expression safe-context — Collection expressions of Span<T>/ReadOnlySpan<T> type now have declaration-block safe-context. Code assigning span collection expressions to variables in outer scopes will error. Use array type or move the expression to the correct scope.

2. ref readonly delegates/local functions need InAttribute — If synthesizing delegates from ref readonly-returning methods or using ref readonly local functions, ensure System.Runtime.InteropServices.InAttribute is available.

3. nameof(this.) in attributes — Remove this. qualifier; use nameof(P) instead of nameof(this.P).

4. with() in collection expressions (C# 15) — with(...) is now treated as constructor arguments, not a method call. Use @with(...) to call a method named with.

5. Dynamic &&/|| with interface operand — Interface types as left operand of &&/|| with dynamic right operand now errors at compile time. Cast to concrete type or dynamic.

6. EF Core Cosmos sync I/O removal — ToList(), SaveChanges(), etc. on Cosmos provider always throw. Convert to async equivalents.

7. SYSLIB0063: NamedPipeClientStream isConnected parameter obsoleted — The constructor overload taking bool isConnected is obsoleted. Remove the isConnected argument and use the new 3-parameter constructor. Projects with TreatWarningsAsErrors will fail to build.

8. when switch-expression-arm parsing — (X.Y) when is now parsed as a constant pattern with a when clause instead of a cast expression, which can cause existing code to fail to compile or change meaning. Review switch expressions using when and adjust syntax as needed.

9. Microsoft.OpenApi v3 breaking changes — Microsoft.AspNetCore.OpenApi now depends on Microsoft.OpenApi 3.x. Code using Microsoft.OpenApi types directly (, , etc.) will have compile errors. Follow the v3 upgrade guide.

Step 4: Address behavioral changes

These changes compile successfully but alter runtime behavior. Review each one and determine impact:

1. DeflateStream/GZipStream empty payload — Now writes headers and footers even for empty payloads. If your code checks for zero-length output, update the check.

2. MemoryStream maximum capacity — Maximum capacity updated and exception behavior changed. Review code that creates large MemoryStreams or relies on specific exception types.

3. TAR header checksum validation — TAR-reading APIs now verify checksums. Corrupted or hand-crafted TAR files may now fail to read.

4. ZipArchive.CreateAsync eager loading — ZipArchive.CreateAsync eagerly loads entries. May affect memory usage for large archives.

5. Environment.TickCount consistency — Made consistent with Windows timeout behavior. Code relying on specific tick count behavior may need adjustment.

6. DSA removed from macOS — DSA cryptographic operations throw on macOS. Use a different algorithm (RSA, ECDSA).

7. Japanese Calendar minimum date — Minimum supported date corrected. Code using very early Japanese Calendar dates may be affected.

8. Minimum hardware requirements — x86/x64 baseline moved to x86-64-v2; Windows Arm64 requires LSE. Verify deployment targets meet requirements.

9. Mono launch target for .NET Framework — No longer set automatically. If using Mono for .NET Framework apps on Linux, specify explicitly.

10. Unhandled BackgroundService exceptions stop the host — Exceptions from ExecuteAsync() now propagate and crash the host. Add try/catch in background services that should not bring down the application.

11. ZipArchive CRC32 validation — ZIP reads now validate CRC32 checksums. Corrupt or truncated archives that previously succeeded will now throw InvalidDataException.

12. TarWriter emits HardLink entries — Hard-linked files are now written as HardLink entries instead of duplicated data. Consumers of .NET-produced tar archives must handle HardLink entries.

13. AIA certificate downloads disabled — Server-side client-certificate validation no longer downloads intermediate CAs via AIA by default. Pre-install the full chain or have clients send intermediates.

14. Blazor Virtualize OverscanCount default changed — Default changed from 3 to 15. Set explicitly if performance-sensitive.

Step 5: Update infrastructure

1. Dockerfiles: Update base images from 10.0 to 11.0:

   # Before
   FROM mcr.microsoft.com/dotnet/sdk:10.0 AS build
   FROM mcr.microsoft.com/dotnet/aspnet:10.0
   # After
   FROM mcr.microsoft.com/dotnet/sdk:11.0 AS build
   FROM mcr.microsoft.com/dotnet/aspnet:11.0
   

2. CI/CD pipelines: Update SDK version references. If using global.json, update the sdk.version in your existing file while preserving other keys (such as rollForward and test configuration):

    {
      "sdk": {
   -    "version": "10.0.100",
   -    "rollForward": "latestFeature"
   +    "version": "11.0.100-preview.3",
   +    "rollForward": "latestFeature"
      },
      "otherSettings": {
        "...": "..."
      }
    }
   

3. Hardware deployment targets: Verify all deployment targets meet the updated minimum hardware requirements (x86-64-v2 for x86/x64, LSE for Windows Arm64).

Step 6: Verify

1. Run a full clean build: dotnet build --no-incremental
2. Run all tests: dotnet test
3. If the application is containerized, build and test the container image
4. Smoke-test the application, paying special attention to:
   • Compression behavior with empty streams
   • TAR file reading (checksum validation and HardLink entries)
   • EF Core Cosmos DB operations (must be async)
   • DSA usage on macOS
   • Memory-intensive MemoryStream usage
   • Span collection expression assignments
   • BackgroundService exception handling
   • mTLS / client certificate chain validation
   • EF Core SQL Server with Entra ID authentication
   • NativeAOT output filenames on Unix
5. Review the diff and ensure no unintended behavioral changes were introduced

Reference Documents

The references/ folder contains detailed breaking change information organized by technology area. Load only the references relevant to the project being migrated: