The ISU has released Communication 2159, which outlines Difficulty Groups for Elements and Additional Features (i.e., Technical Requirements) for the 2018-19 season. This Communication replaces 2121. Remember, this is the document that tells you what you have to do to get credit for a certain level. More documents will be released later that go into detail about the penalties for not executing something correctly. See Demystifying the Judging System: Roles, Rules & Reports Cards (Part 2 of 3) for more information on the order in which documents are usually released.
Presumably, there could be revisions to 2159 after Congress is held in June. If you’re up for some light reading, the 135-page Congress agenda and proposals can be found in Communication 2156.