Whenever Blizzard releases a new World of Warcraft expansion, the content within that expansion is typically staggered. This means that for the most part, the core of the expansion will be released such as all the new quests, zones, races, classes, and so on, but in terms of end-game content like raids, those are usually released in phases.
It seems that those same rules will apply to World of Warcraft Classic, according to a report from Polygon who managed to speak to World of Warcraft’s game director Ion Hazzikostas during BlizzCon 2018. According to Hazzikostas, the raid content in Classic will also be released in various stages, starting with stage 1.
This will give players access to the Molten Core and Onyxia’s Lair raids, along with the Dire Maul dungeon and world bosses such as Lord Kazzak and Azuregos. Stage 2 will be released later and will open up the 40-player Blackwing Lair raid and Zul’Gurub, and stage 3 will see the release of Ahn’Qiraj (along with the world event) and other content surrounding Silithus.
Last but not least will be stage 4 where it will involve the Naxxramas raid and the Scourge invasion world events. There is no word on when these stages will be released, or how frequently they will be released, but hopefully we’ll have more details soon. In the meantime World of Warcraft Classic is expected to be made available come the summer of 2019.