The 2 GB object size limitation has been lifted in .NET 4.5 64-bit

Great news: if you have ever wanted to access objects larger than 2 GB in your .NET applications on 64-bit platforms, this is now finally possible with .NET 4.5. Previously, trying to do this (even if you had plenty of memory available) resulted in an OutOMemoryException exception.

Quote from a blog post on MSDN:

"In the .NET Framework 4.5, this limit has been lifted on 64-bit platforms. The limit remains in place on 32-bit machines, due to the 32-bit address space."

Excellent!