The recent beta 8 release of ASP.NET 5 MVC 6 has resulted a few renames.
This post contains some of the ones I have come across so far.

##Sessions
Beta 8 brings back the HttpContext property which replaces the Context property.

HttpContext.Session.SetString("example1", "myString"); 
Old(er) Beta 8
Context HttpContext
Context.Session.Set(String, byte[]) HttpContext.Session.SetInt32(String, byte[])
Context.Session.Get(String) HttpContext.Session.Get(String)
Context.Session.SetString(String, String) HttpContext.Session.SetString(String, String)
Context.Session.GetString(String) HttpContext.Session.GetString(String)
Context.Session.SetInt32(String, int) HttpContext.Session.SetInt32(String, int)
Context.Session.SetInt32(String) HttpContext.Session.SetInt32(String)

##Diagnostics
Error pages provided by diagnostics have better names to avoid confusion.

app.UseDeveloperExceptionPage();
Old(er) Beta 8
app.ErrorHandler() app.UseExceptionHandler()
app.ErrorPage() app.UseDeveloperExceptionPage()