Valve has released the beta client for Dota 2, which moves it to the Source 2 engine and adds a number of modern enhancements and the ability to create custom games.
You can check out the full breakdown of new features at the Dota 2 website, but the move to the new engine promises a host a improvements to performance, including decreased latency in mouse-click actions and multi-threading support. A big focus is the ability for content creators to create custom games for Dota 2, and the Source 2 engine offers a variety of options for map creators, such as a tile-based map system and new rendering engine that allows custom geometry and more.
A few network improvements have also been touted, including a complete move off the public IP address space to minimise the opportunities for Direct Denial of Service (DDoS) attacks.
You can check out the custom games video below (which was made in the newly updated Source Filmmaker, which now has access to the Source 2 engine.). Scroll right down to the bottom of the Dota 2 website for instructions on how to install the beta.
Source: Dota 2