https://wccftech.com/wow-tbc-classic-beta-imminent-datamine/

A reference to an internal alpha TBC Classic beta might hint at the expansion’s beta being close to release.

Last week, Blizzard announced that World of Warcraft’s first official expansion, The Burning Crusade, will be getting a Classic server option later this year in the form of TBC Classic. As confirmed, current WoW Classic servers will migrate to TBC Classic but prior to the launch of the expansion, players will get the opportunity to choose which characters they want to keep in the Vanilla Era version.