The MP9 | Music Box is a Mil-Spec SMG skin from The 2021 Mirage Collection, distributed through the Stockholm 2021 Mirage Souvenir Package.

The float range for this finish is restricted to 0.00–0.55, so Factory New, Minimal Wear, Field-Tested, Well-Worn, and Battle-Scarred are the only obtainable conditions on the open market. The restricted range is set by Valve at the time of release.

A Souvenir version is available, dropped exclusively from cases collected during Major Championship matches and stamped with that tournament's stickers. Active listings for MP9 | Music Box are tracked across 17 marketplaces, with prices spanning $0.13 to $330.12 depending on wear, variant, and seller.