Over the weekend we installed ASP.NET 4 on all the servers in our MaxESP server farm. To create a new ASP.NET 4 site, simply choose it from the options when you create a new site. On existing sites, you can change it in your site options.
We’ve been running a public beta for ASP.NET 4 in partnership with Microsoft over the past 5 months. This has allowed us, and our customers, to become experts well in advance of its release. We are excited to put all the new features into the hands of our customers.