That is a question for the manufacturer. It is likely to give the end user the option to pin and weld it themselves or use the upper for a pistol or SBR build.
It is pinned and welded, mine came with a Surefire Warcomp.
It is pinned and welded. I just bought one in the Midnight Bronze and the BattleComp 1 is beautifully pinned and welded on. This is a STELLAR UPPER for the $, btw. I'm fortunate to own and run some BCM/DD/POF/LWRC's etc and I can easily say that this ADM and my POF's give you way more rifle and features for the $ than BCM, DD or LWRC. Not saying they're not reliable, rock solid and/or battle proven (any rifle $1500 and up will be G2G). ADM & POF just gives you nicer, more modern features over BCM, DD, etc (like nitrided barrels and BCG's, ambi charging handles, fully ambi controls, MBus Pros, polished chamber and feed ramps, heat sink barrel nut, e2 chambering, adjustable gas blocks, billet over forged, etc. YMMV). Grab one for sure! #WWG1WGA