Apparently not a linear deceleration.
"Brake-to-vacate combines satellite positioning with the aircraft's on-board airport database and flight-control systems to provide crews with braking distances to their preferred runway exit.
Once the pilot has selected a runway exit point, the system manages the deceleration - taking into account runway surface - in order to ensure the jet reaches the exit at the correct vacate speed.
… the system takes into account several elements - not just the aircraft's speed and position but also the temperature, wind and runway elevation."
https://www.flightglobal.com/easa-cl.../89832.article
https://skybrary.aero/sites/default/...helf/33873.pdf
Related:
https://safetyfirst.airbus.com/app/t...ion-system.pdf