The W3C has announced that the following documents are now W3C Candidate Recommendation Snapshots:
EPUB 3 defines a distribution and interchange format for digital publications and documents. The EPUB format provides a means of representing, packaging, and encoding structured and semantically enhanced web content — including HTML, CSS, SVG, and other resources — for distribution in a single-file container.
The full W3C announcement explains this important development in more details and provides information for implementation and feedback.
Our article What Does EPUB 3.3 Mean For Accessibility explores the new version of the standard and you may also be interested in the recent TechForum webinar The Year of Testing Dangerously where Wendy Reid (Kobo) and Dave Cramer (Hachette), co-chairs of the W3C working group, discuss the new specs in more detail.