The new Download Manager will list all of your mods with available updates so that you can easily install them with a single button press. Developers can also view debug information on their mods to see what is being loaded and processed. Mods now have their own info page accessible from the mod manager so that you can easily turn your mods on or off, and set or check for updates to them. Any mods not supported by the new version of the BLT will be highlighted red so you can find and remove them easily. The mod manager has completely changed so that you can more easily view all of your mods and configure them quickly. Get the updated BLT from the Download page.
This means your mods might be broken until the mod developer updates them. The in-game mod loader has been completely rewritten from scratch so that it is easier to use for users to understand, and easier for developers to get started with.
The BLT has been updated to support LuaJIT in Payday 2, and the BLT has changed massively thanks to a huge update.