For Version 3.3 and higher
From the introduction:
This guide is meant to provide an overview of the core Nucleus rules and character creation for new Nucleus GMs. It is delibratly brief, for more details see the full rule book.
The "Version 4" release of this product supported the last few releases of the Version 3 rules (Versions 3.3, 3.4, and 3.5) as well as the release of the Version 4 rules.