Arch is the CPU architecture, amd64 or arm64, and it is what decides whether a binary built for the fleet will run here. Only the sources that report one carry it (a linked run-target, a BYO worker).
GPUModel names the FIRST accelerator ("NVIDIA GB10") as the representative of the set; GPUs carries how many. Empty for a cluster, whose cards are counted rather than modelled, and for a unit with none.
Memory is total system RAM in BYTES — not GB, and not what is free right now (fleetMetrics carries that). Absent when the source reports no RAM figure.