Web API Preview 5 Is Now Available

New Features/Enhancements

OData Formatter
Dependency refactoring from host common code
Support for Batch with mime/mixed content where every part has a full HTTP request
Web API code-based configuration (simplifications)
Web-based test client for WCF Web API
HTTP File upload
Refactored formatters
Better IoC support
Additional samples for specific features such as file upload
Content negotiation now supports qualifiers
ActionOfStreamContent - Enables accessing the raw content stream
New HttpMemoryBinding to enable in-memory hosting and invoking of Web APIs

New Prototype Features (on WebAPI-Prototype branch)

WebApiConfiguration includes conventions for WebGet/WebInvoke
WebApiRoute provides better side by side integration with MVC routes
MapServiceRoute extension method simplified registration and usage of WebApiConfiguration
SetDefaultHttpConfiguration / GetDefaultHttpConfiguration extension methods enable the getting and setting of a global configuration object that will be used by default by
MapServiceRoute unless a specific one is provided
MediaTypeFormatterCollectionExtensions.AddRange enables a more compact way to add formatters
FormUrlEncodingMediaTypeFormatter
Task<T> for Web API operations and sample

Breaking Changes

DelegatingChannel renamed to DelegatingHandler
HttpChannel renamed to HttpMessageHandler
FormUrlEncodingMediaTypeFormatter and JsonValueMediaTypeFormatter were moved from the default branch to the WebAPI-Prototype branch as they are not currently part of the core product source
DelegatingHandler no longer require passing in a channel in the constructor making it more friendly to inversion of control (IoC) containers
New constructor overload on HttpMessageHandlerFactory overload which accepts a Func<IEnumerable<DelegatingHandler>> to allow user code or IoC containers to construct handlers.
IQueryable previously supported case-insensitive matches on operators. In the current drop we only will match on lowercase operators i.e. "$top" but not "$Top". According to the spec this is correct behavior however we could relax it in the future.

Nuget

Like I mentioned above, preview 5 is also being released on Nuget today. Here's the breakdown of the Nuget packages that will be available:

HttpClient : like it sounds, this gives you the HttpClient object model, which can be used by both the server and the client for a symmetric HTTP programming experience.
JsonValue : Contains JsonValue API for typeless / dynamic access to Json.
WebApi : The server-side object model for Web API
WebApi.All : Preserved for backwards compatibility; basically just pulls in everything.
WebApi.Core : Preserved for backwards compatibility; pulls in WebApi.0.5.0
WebApi.Enhancements : Gives you the Web API core product code plus the enhancements library (from the prototype branch)
WebApi.OData : Enables returning OData from a Web API.

In addition to the core Nuget packages, we're also pushing up a set of symbol packages so that you can more easily debug through Web API source code.

HttpClient.0.5.0.symbols.nupkg
JsonValue.0.5.0.symbols.nupkg
WebApi.0.5.0.symbols.nupkg
WebApi.Enhancements.0.5.0.symbols.nupkg
WebApi.OData.0.5.0.symbols.nupkg

Reference:

http://codebetter.com/howarddierking/2011/09/15/web-api-preview-5-is-now-available/
http://nuget.org/packages?q=webapi
http://wcf.codeplex.com/releases/view/73423