Quick answer
Current Playtest snapshotSteamDB currently reports the AION 2 Playtest depot at about 80.42 GiB to download and 81.74 GiB on disk. Steam officially lists 100 GB of available storage for the main Global game.
Is 80.42 GiB the final AION 2 launch download size?
No final retail transfer size yetThe 80.42 GiB number belongs to the current Steam Playtest depot snapshot, not a promise that the September 30 or October 5 retail client will download exactly the same amount. The depot can still change.
What should you clear before preload?
For the Launch Scale Test, clearing at least the official 100 GB requirement is the low-risk choice. Leave additional headroom if possible because game clients can need temporary space while patching or unpacking.
Steam vs PURPLE caveat
The SteamDB figure is specifically for the Steam Playtest app. It should not be presented as a measured PURPLE transfer size. NC has not published a separate exact PURPLE download-size number in the current official test notice.