Different models are available for different workloads and use cases:
X5-6500 - HCI Flash Accelerator Node 2U
X5-6000 - HCI Flash Standard Node 2U
X5-6000s - STO Flash Storage-only Node 2U
X5-2500 - HCI Hybrid Accelerator Node 2U
X5-2000 - HCI Hybrid Standard Node 2U
X5-2000s - STO Hybrid Storage-only Node 2U
X3-6500 - HCI Flash Accelerator Node 1U
X3-6000 - HCI Flash Standard Node 1U
X3-6000s - STO Flash Storage-only Node 1U
X3-2500 - HCI Hybrid Accelerator Node 1U
X3-2000 - HCI Hybrid Standard Node 1U
X3-2000 - STO Hybrid Storage-only Node 1U

A Pivot3 Acuity cluster always has to include 2 Accelerator nodes (either X5-6500, X5-2500, X3-6500 or X3-2500), because NMVe PCIe is used as write-buffer and all writes are mirrored between these two nodes.

Pivot3 X-Series Storage Appliances are combined with Pivot3 X-Series HCI Appliances to form a Virtual Performance Group (vPG).