.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

Input	Required	Description
Project or solution path	Yes	The `.csproj` , `.sln` , or `.slnx` entry point to migrate
Build command	No	How to build (e.g., `dotnet build` , a repo build script). Auto-detect if not provided
Test command	No	How to run tests (e.g., `dotnet test` ). Auto-detect if not provided
Project type hints	No	Whether the project uses ASP.NET Core, EF Core, Cosmos DB, etc. Auto-detect from PackageReferences and SDK attributes if not provided

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

Identify how the project is built and tested. Look for build scripts,
```
.sln
```
/
```
.slnx
```
files, or individual
```
.csproj
```
files.
Run
```
dotnet --version
```
to confirm the .NET 11 SDK is installed. If it is not, stop and inform the user.
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
Record which reference documents are relevant (see the reference loading table in Step 3).
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

In each

.csproj

(or

Directory.Build.props

if centralized), change:

xml

<TargetFramework>net10.0</TargetFramework>

to:

xml

<TargetFramework>net11.0</TargetFramework>

For multi-targeted projects, add

net11.0

<TargetFrameworks>

or replace

net10.0

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.
Run
```
dotnet restore
```
. Fix any restore errors before continuing.
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:

Reference file	When to load
`references/csharp-compiler-dotnet10to11.md`	Always (C# 15 compiler breaking changes)
`references/core-libraries-dotnet10to11.md`	Always (applies to all .NET 11 projects)
`references/sdk-msbuild-dotnet10to11.md`	Always (SDK and build tooling changes)
`references/aspnetcore-dotnet10to11.md`	Project uses ASP.NET Core (OpenAPI, Blazor)
`references/efcore-dotnet10to11.md`	Project uses Entity Framework Core
`references/cryptography-dotnet10to11.md`	Project uses cryptography APIs, mTLS, or targets macOS
`references/runtime-jit-dotnet10to11.md`	Deploying to older hardware, embedded devices, or using NativeAOT

Work through each build error systematically. Common patterns:

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.
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.
nameof(this.)
in attributes — Remove
```
this.
```
qualifier; use
```
nameof(P)
```
instead of
```
nameof(this.P)
```
.
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
```
.
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
```
.
EF Core Cosmos sync I/O removal —
```
ToList()
```
,
```
SaveChanges()
```
, etc. on Cosmos provider always throw. Convert to async equivalents.
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.
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.
Microsoft.OpenApi v3 breaking changes —
```
Microsoft.AspNetCore.OpenApi
```
now depends on
```
Microsoft.OpenApi
```
3.x. Code using
```
Microsoft.OpenApi
```
types directly (
```
OpenApiDocument
```
,
```
OpenApiSchema
```
, etc.) will have compile errors. Follow the v3 upgrade guide.
EF Core Design package no longer transitive —
```
Microsoft.EntityFrameworkCore.Tools
```
and
```
.Tasks
```
no longer depend on
```
.Design
```
. Add an explicit
```
PackageReference
```
if needed.
EFOptimizeContext MSBuild property removed — Replace with
```
<EFScaffoldModelStage>
```
and
```
<EFPrecompileQueriesStage>
```
.

Step 4: Address behavioral changes

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

DeflateStream/GZipStream empty payload — Now writes headers and footers even for empty payloads. If your code checks for zero-length output, update the check.
MemoryStream maximum capacity — Maximum capacity updated and exception behavior changed. Review code that creates large MemoryStreams or relies on specific exception types.
TAR header checksum validation — TAR-reading APIs now verify checksums. Corrupted or hand-crafted TAR files may now fail to read.
ZipArchive.CreateAsync eager loading —
```
ZipArchive.CreateAsync
```
eagerly loads entries. May affect memory usage for large archives.
Environment.TickCount consistency — Made consistent with Windows timeout behavior. Code relying on specific tick count behavior may need adjustment.
DSA removed from macOS — DSA cryptographic operations throw on macOS. Use a different algorithm (RSA, ECDSA).
Japanese Calendar minimum date — Minimum supported date corrected. Code using very early Japanese Calendar dates may be affected.
Minimum hardware requirements — x86/x64 baseline moved to
```
x86-64-v2
```
; Windows Arm64 requires
```
LSE
```
. Verify deployment targets meet requirements.
Mono launch target for .NET Framework — No longer set automatically. If using Mono for .NET Framework apps on Linux, specify explicitly.
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.
ZipArchive CRC32 validation — ZIP reads now validate CRC32 checksums. Corrupt or truncated archives that previously succeeded will now throw
```
InvalidDataException
```
.
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.
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.
Blazor Virtualize OverscanCount default changed — Default
```
OverscanCount
```
changed from 3 to 15. Set explicitly if performance-sensitive.
Microsoft.Data.SqlClient 7.0 — Entra ID auth separated — Azure/Entra ID authentication dependencies removed from the core SqlClient package. Add
```
Microsoft.Data.SqlClient.Extensions.Azure
```
if using Entra ID auth.
SqlVector<T> excluded from SELECT — Vector properties are no longer auto-loaded. Use explicit projections to include vector values.
SQLitePCLRaw encryption bundles removed —
```
bundle_e_sqlcipher
```
and other encryption bundle packages removed in SQLitePCLRaw 3.0.
NativeAOT Unix native library
lib
prefix — Output filenames now include
```
lib
```
prefix on Linux/macOS (e.g.,
```
libMyLib.so
```
).

Step 5: Update infrastructure

Dockerfiles: Update base images from 10.0 to 11.0:

dockerfile

# 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

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):

diff

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

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

Run a full clean build:
```
dotnet build --no-incremental
```
Run all tests:
```
dotnet test
```
If the application is containerized, build and test the container image
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
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:

Reference file	When to load
`references/csharp-compiler-dotnet10to11.md`	Always (C# 15 compiler breaking changes)
`references/core-libraries-dotnet10to11.md`	Always (applies to all .NET 11 projects)
`references/sdk-msbuild-dotnet10to11.md`	Always (SDK and build tooling changes)
`references/aspnetcore-dotnet10to11.md`	Project uses ASP.NET Core (OpenAPI, Blazor)
`references/efcore-dotnet10to11.md`	Project uses Entity Framework Core
`references/cryptography-dotnet10to11.md`	Project uses cryptography APIs, mTLS, or targets macOS
`references/runtime-jit-dotnet10to11.md`	Deploying to older hardware, embedded devices, or using NativeAOT

migrate-dotnet10-to-dotnet11

NPX Install

Tags

SKILL.md Content