“[I]t will be difficult for us to release a new class at the start of each new season, but if it is possible, we want to go in a direction where we can aid our Adventurers’ growth as much as we can. For the reasons above, the end date of the Summer Season will be moved ahead of the originally announced date to an earlier date of the August 26th (Wed) maintenance. We understand that some Adventurers who are currently playing on the season servers may feel pressured to grow their character as a result of the earlier end date. To help these Adventurers out, we are preparing events where you can obtain a variety of necessary items to grow your character during the Summer Season. In addition, if you’re an Adventurer who feels their time in the season servers is sufficient, you’ll be able to graduate early from the summer season after the maintenance on August 5th (Wed).”
In other words, starting next week, you can “graduate” from the servers, but they definitely end on August 26th, when pre-creation for the Hashashin begins, and then the class launches September 2nd.