The OASIS Cyber Threat Intelligence Technical Committee (CTI TC) passed the ballots for STIX 2.0 and TAXII 2.0 in July, 2017. OASIS staff is currently finalizing the documents to ensure compliance with OASIS trademark-related legal requirements. A note from OASIS:
For those data scientists and programmers seeking a pre-authoritative version to use for development purposes, I’ve created links to the versions approved by the technical committee.
Below are the links to the 5-part specification for STIX 2.0 and 1-part specification for TAXII 2.0.
See also the GitHub Repository for an Open Source TAXII 2.0 Server.