Cannot find JavaScriptSerializer in .Net 4.0

I cannot seem to find the JavaScriptSerializer object nor the the System.Web.Script.Serialization namespace within Visual Studio 2010. I need to serialize something to JSON what am I supposed to use?

And yes, I already included the System.Web.Extensions (in System.Web.Extensions.dll) within the project. Which is why I am shocked?

• I do know System.Web.Extensions was marked as obsolete in 3.5