Run trillian-v4.0a-current.exe to install Trillian and once it's done choose Launch at the end page.
If you haven't set up an account yet click on New Account and select Log In Existing Account, enter some bogus details in the Name and Password boxes (this information won't be used anyway). Then choose Log In.
Enjoy the program!

-Cracked by Homer


Official Release notes

Build 103
UPDATE: Build 103 has been released to address a regression issue with the Facebook plugin. Users of Facebook Chat will need to re-enter their passwords in preferences. Build 103 will be rolled out throughout the weekend.

Build 102
Build 102 is now available. As some of you have noticed, we’ve been adding a large number of new testers to the beta team this week. We wanted to take a minute to welcome all of the new testers and briefly explain how the build process works!

Today’s release of Build 102 follows our typical release schedule:

1. Internal milestones for a build are met, and the team packages up the next build for testers.
2. Testers begin receiving the build via automatic update over the course of the next few days. Not everyone will receive the build at the same time!

Those of you with Trillian Pro can enable the “Check for beta versions of Trillian” preference to receive the build at the earliest possible opportunity. As we have no final product yet, this preference currently functions as a way to divide “alpha” builds of a beta and “final” builds of a beta. Upon final release, this preference will divide 4.0 releases and subsequent betas of 4.1 and beyond.

Thanks for your support and we hope you enjoy the new build!