You can now from the Technet Evaluation Center. I have not seen any posts or documentation detailing anything specific to the 4th preview, so it must have just been released. Hopefully they have fixed a bug that I have found in the 3rd T.P. where the application catalog and the application catalog web service roles will not install because of a IIS version check error. I have been getting the error that IIS version 7 or above must be installed, however version 10 is installed along with all of the required prerequisites, so I am about to install it and check what has changed in this new preview version.
As with the other technical preview versions of configuration manager, this preview is also only good for 60 days, and upgrades are not supported, (which is annoying if you have been using the 3rd technical preview. I am going to have to uninstall the TP 3 before installing the 4th Technical preview.