Hello William, Yes the Glock 21 Gen 4 features one available slot for mounting accessories. Hope this helps and enjoy the rest of your day!

William, it does but it is only a single slot, so if it were me i would start looking into lights or lasers that are fairly small.

Yes it does.

Hi William and welcome. Yes Sir. It has a single slot accessory rail as pictured here: guns.com/firearms/p/glock-g21-g4-45acp-13-1-fs-3-13rd-mags-accessory-rail-45-acp?i=124402 ---------- Cheers and stay safe!

Hi William, yes, the Glock 21 Gen 4 features a rail for mounting accessories, allowing for the attachment of lights and other devices.
Stay safe & have a great day!