Valve has announced on the official Defense of the Ancients 2 page that the upcoming First Blood update will be landing on the 23rd September, and will add LAN support.
According to the studio, players will be able to "create a local lobby and use (their) computer to host a rousing round of Dota 2 through their" home or café network."
The other additions include Captain's Draft, which is sort of the DOTA equivalent of a sealed deck draft, where players take turns claiming heroes from a random pool of 24 to form their teams. The Backpack adds an inventory filter to quickly find items.
Check out the official page.