Stock firmware date rule
For S21/T21 generation miners, the Bitmain stock firmware date matters. Direct VOU installation is safest on allowed stock windows; restricted builds may require stock recovery or downgrade steps before VNISH.
Antminer S21 guide
VNISH firmware for Antminer S21 series
Use this guide to plan S21, S21+, S21 Pro, S21 XP, hydro and immersion installs. These variants can have different board checks, cooling profiles and stock-firmware rules.
S21 / S21+S21 Pro / XPHydro / ImmersionAML / CV / XIL
| Variant | Typical focus | Install note |
|---|---|---|
| S21 / S21+ | Efficiency and power-limit tuning | Confirm AML/CV board before package selection |
| S21 Pro | High baseline hashrate | Keep initial targets conservative until autotune finishes |
| S21 XP | Thermal control and PSU headroom | Do not push overclock before stable chip map |
| S21 Hydro / Immersion | Cooling profile and pump/fan logic | Use the matching hydro/immersion build only |
First tune strategy
Use a lower power target for the first autotune run, watch inlet/outlet temperature and reject-rate behavior, then raise the target gradually.
Farm rollout
For more than a few S21 units, group miners by exact model and control board before bulk install. Keep a small pilot batch online for a full shift before touching the next rack.
Frequently asked questions
Why does S21 need a separate guide?+
S21 firmware packages and stock-date rules are more sensitive than older S19 units, especially with hydro and immersion variants.
Can VOU update an existing VNISH S21?+
Yes, for supported VNISH installs. Use update only when VNISH is already installed; use install for clean flashing.
What is the safest S21 first profile?+
A conservative efficiency target with full autotune and thermal monitoring before any overclock.
Related VNISH guides
Continue through the model, install and recovery pages before flashing production miners.