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Bitmain Antminer S21 Immersion firmware guide

Stock firmware + trusted custom firmware options for Bitmain Antminer S21 Immersion. Includes compatibility checklist, safe update steps, and direct source links.
Firmware options commonly associated with this model include: Bitmain Antminer stock firmware, Braiins OS+. Use this page as a checklist: confirm control board compatibility, download only from official sources, and keep a rollback plan to stock firmware.
Open model page Search in catalog Safe update checklist
Entries
3

1) Confirm exact model and control board

Before downloading anything, confirm the exact sub‑model (suffixes, “Hydro/Immersion”, regional variants) and identify the control board generation. A wrong board match is the #1 cause of failed flashes.
  • Check the miner web UI for hardware/firmware information.
  • Inspect the control board label or markings if the vendor requires it.
  • If a firmware page lists supported boards, treat it as mandatory.
Control board compatibility checklist Rollback & recovery

2) Choose stock vs custom firmware

Stock firmware is the safest baseline and the main recovery path. Custom firmware can add autotune, power profiles and monitoring — but requires stricter compatibility checks.
A practical approach:
  1. If you’re troubleshooting or unsure about compatibility, start with stock firmware.
  2. Once stable, consider a custom firmware for efficiency/tuning — one miner at a time.
  3. After flashing, monitor temperatures, HW errors and pool hashrate before enabling aggressive profiles.
Stock firmware overview Autotune explained Undervolt/overclock basics Monitoring & stability

3) Source links for Bitmain Antminer S21 Immersion

Below are the firmware entries and source links listed for this model in our directory. Use the official link as the primary download location. The evidence link usually points to a compatibility list, release note or documentation page.
FirmwareTypeLinksNotes
Bitmain Antminer stock firmwareStockofficialOfficial download center; choose the exact miner type/model before updating.
Braiins OS+Customofficial · evidenceAutotuning / power‑limit tuning; compatibility depends on the control board.
Braiins OS+Customofficial · evidenceAutotuning / power‑limit tuning; compatibility depends on the control board.
For the full list (including search phrases and tags), open the model page.
Model page: Bitmain Antminer S21 Immersion

4) Safe flashing steps (short version)

  1. Download from the official source and read the vendor instructions for your control board.
  2. Backup current settings (pools, power limits). Update one miner first.
  3. Flash via web UI or the recommended tool. Wait for reboot; don’t power‑cycle mid‑flash.
  4. Validate stability: all hashboards detected, temperatures stable, errors low, pool hashrate consistent.
  5. Only then apply autotune/overclock profiles — in small steps.
Full update checklist Rollback & recovery

FAQ

Where do I download Antminer S21 Immersion firmware?
Use the official links above (manufacturer portals or official vendor pages). Avoid re‑uploaded archives and unofficial mirrors.
What if the miner doesn’t boot after flashing?
Follow rollback/recovery steps: try web‑UI rollback if available, otherwise SD recovery (if supported) or vendor rescue tools. Keep stock firmware ready.
Will custom firmware increase profit?
It can — mainly via better efficiency (hash/W) and uptime. Results depend on electricity price, cooling, and conservative tuning.