Mike, the Gen3 Glock 20 comes with (2) 15rd Magazines Sir.

Mike, Gen 3 Glocks 'This Model' ship with 2 magazines. All Gen 4 and Gen 5 Glocks ship with 3 magazines.

The UPC and model number crosses to a GEN 4 and comes with 3 mags
G20 G4 10MM 15+1 4.61" FS
3-15RD MAGS | ACCESSORY RAIL
10mm
UPC: 764503802034 MFG MDL #: PG2050203
PG2050203 PRODUCT DETAILS
FAMILY:G20 Series
MODEL:G20 G4
TYPE:Semi-Auto Pistol
ACTION:Safe Action
FINISH:Gas Nitride
STOCK/FRAME:Polymer Frame
WEIGHT:30.71 oz.
CALIBER/GAUGE:10mm
CAPACITY:15 + 1
********* # OF MAGS:3
MAGAZINE DESC:15 rd.
BARREL:4.60"
OVERALL LENGTH:8.03"
SIGHTS:Fixed Glock Sights
SAFETY:No Manual Safety
GUN CASE:Plastic

Hi Mike, This Glock 20 includes (2) 15 Round Magazines.