From what I recall, we have two live letters before each major patch. This will be the first, the other will be the second with more detail.

Major patches have always been split into parts, dragging out the content between them. For example:
7.1
7.11
7.15
7.18
Don't believe me? Check the entire list of patches on the official website https://na.finalfantasyxiv.com/lodes...patchnote_log/