Leak ? 
If you check Band pages currently indexed on Google for graspop.be (
https://www.google.com/search?q=site:graspop.be inurl:bands ), there are only about 100 pages indexed (so, any other bands from past editions are not visible there), including the already confirmed headliners. Here are the ones that are indexed:
1349, 36 Crazy Fists, After All, Alchemist, All Shall Perish, Amplifier, Armored Saint, As Lions, As It Is, At The Gates, Atheist, Axamenta, Ayreon, Back To The System (SOAD Tribute), Backfire, Battlecross, Behemoth, Beyond Fear, Bombshell Rocks, Borknagar, Born From Pain, Brides of Destruction, Bruce Dickinson, Bulls On Parade (RATM Tribute), Cannibal Corpse, Caliban, Calibre, Carcass, Carnation, Celeste, Celtic Frost, Civil War, Collibus, Congress, Cowboys And Aliens, Crobot, Cult of Luna, Culture Abuse, Cynic, Danzig, Darkane, Dead Cross, Death By Stereo, Dedicted,
Def Leppard, Destruction, Devilment, Diablo Blvd, Disfear, Dismember, Downset, Drain, Dream Theater, Dublin Death Patrol, Dyscordia, Endless Dark, Enslaved, Equilibrium, Eternal Run For Cover, Evergrey,
Faith No More, Farmer Boys, Fintroll, FM, Forbidden,
Ghost, Glorior Belli,
Gun's N Roses, Hail of Bullets, Halford, Handsome, Hardline, Hawkwind, Heidevolk, Heilung, Helmet, Hollenthon, Huntress, I Killed The Prom Queen, Ill Nino, In Quest, In Solitude, In The Woods, Jonathan Davis, Killing Machine, Kill II This, Komah, Korn Again, Krypteria, Leave Scars, Legion Of The Damned, Leng Tch'e, Massif, Me First & The Gimme Gimmes, Metal Church, Ministry, Misthyrming, Monuments, Moonsorrow,
Mötley Crüe, Mucky Pup, Murderdolls, Myrkur, Nasum, Necrophobic, Nile, No Use For A Name, Northlane, Novembers Doom, Nuclear Assault, Orchid, Orphanage, Orphaned Land, Ostrogoth, Our Survival Depends On Us, Out, Panchrysia,
Parkway Drive, Parris (Thin Lizzy Tribute), Periphery, Peter Pan Speedrock, Playmo, Powerstroke, Power Trip, Prime Circle, Prong, Protest The Hero, Revoker, Rage, Rise To Remain, Rockstar, Rotting Christ, Scar Symmetry, Scarve, Schirenc Plays Pungent Stench, Sebastian Bach, Set Things Right, Seven Witches, Shai Hulud, Six Feet Under, Skarhead, Skin, Skindred, Skitsoy,
Slipknot, Soilwork, Spoil Engine, Spoiler NYC, Stahlzeit, Stake, Static-X, Stormrider, Stratovarius, Stream Of Passion, Subzero, Taake, Tempt, Temptations For The Weak, The Devils Blood, The Difference, The Gathering, The Faceless, The New York Dolls, The Ocean, The Rods, The Sword, The Treatment, The Vandals, Therion, Touché Amoré, Trash Boat, Turisas, UDO, Uncle Acid And The Deadbeats, Uncle Meat, Underoath, Unearth, Van Hagar, Veil Of Maya, Voodoo Six, Wednesday 13, Welkin, Witchsmeller Pursuivant, Youth Of Today
Not sure this is reliable (perhaps this is just a draft from 6 months ago), but I think most of those bands are relevant for 2023.
