EPUB 3.0.1 is the current version of the EPUB standard. It is a minor maintenance update to EPUB 3.0 . On June 26, 2014 the IDPF announced that the IDPF membership had overwhelmingly approved elevation of EPUB 3.0.1 to final Recommended Specification status.
EPUB 3.0.1 was developed pursuant to a charter approved by the IDPF Membership in May, 2010. and approved by the IDPF membership as a final Recommended Specification effective October 11, 2011. Changes between EPUB 3.0.1 and EPUB 3.0 are documented here. The more extensive changes between EPUB 3.0 and EPUB 2.x are documented here.
EPUB 3.0.1 is defined by a set of individual specifications. The best starting point for learning about EPUB 3.0.1, including the roadmap to the specification documents, is the EPUB 3 Overview .