Blizzard has stated that PTR Patch Notes for Diablo 4 will likely be revealed this Thursday, March 28 — but these patch notes will not include the full list of Season 4 changes.
Global Community Development Director Adam Fletcher responded to a recent Reddit thread regarding when PTR patch notes would be released, stating that Blizzard is aiming to release them this Thursday:
Patch Notes Thread on Reddit
While Fletcher's language does leave room for a delay, it's likely that we'll see the PTR notes this Thursday — after all, the first PTR in Diablo 4 history begins next week and will run for a week from April 2 until April 9.