Beginning June 22, 2010 the .NET Framework 4 is available through WIndows Update to ease deployment.
The whole framework? No, only the "light" version, so called "Client Profile", which contains the features to develop a client application, including:
Common language runtime (CLR)
Windows Presentation Foundation (WPF)
Windows Communication Foundation (WCF)
Windows Workflow Foundation
LINQ to SQL
Runtime design libraries for Entity Framework and WCF Data Services
Managed Extensibility Framework (MEF)
Parallel-programming features, such as Task Parallel Library (TPL), Parallel LINQ (PLINQ), and Coordination Data Structures (CDS)
Debugging client applications
It does not include (meaning you still need to install the full .NET Framework 4.0 to use those features), for example:
Advanced Windows Communication Foundation (WCF) functionality
.NET Framework Data Provider for Oracle
MSBuild for compiling
Now, it's on Windows update, will it install automatically?
It depends on the Windows Update settings, "the .NET Framework 4 Client Profile is released as a recommended update that may be installed automatically on Windows Vista and Windows 7. The Client Profile is released as an optional update for Windows XP. In Windows XP, you must manually run WU and select the .NET Framework 4 Client Profile".
.NET Framework 4 Client Profile:
- Recommended Update on Windows Vista/7
- Optional Update on Windows XP
Full .NET Framework 4:
- Optional Update on Windows Server 2003, Windows Server 2008 and on Windows Server 2008 R2