The current General Availability (GA) release is WSJT-X 2.0.0
The FT8 and MSK144 protocols have been enhanced in a way that is not backward compatible with older program versions. The new protocols become the world-wide standards starting on December 10, 2018, and all users should upgrade to WSJT-X 2.0 by January 1, 2019. After that date, only the new FT8 and MSK144 should be used on the air.
For FT8, WSJT-X 2.0.0 will decode the messages sent by earlier releases and respond with the corresponding older message format. However, for MSK144 (often used for meteor scatter), the payloads are incompatible and 2.0 will not decode messages sent from pre 2.0, and vice-versa.
See https://physics.princeton.edu/pulsar/k1jt/wsjtx.html for details and download.
For those of you that also use JTAlert with WSTJ-X, there is a later version 2.12.10. See https://hamapps.com/ for details and download.
Simon Watson