Great news!
If he really did have City and/or Liverpool in his ear then we're very lucky he's chosen to remain loyal over what would have, in my opinion, been a better career choice.
Hopefully, it's a new era at Arsenal and we actually help the kid to grow into top player in whichever is his best position, don't run him into the ground and ruin him as a result, and put a team around him that gives him the opportunity to thrive.