Antminer S21 Family Owner's Hub: Every Variant, Spec, Firmware, Fix and Upgrade

Quick answer

The Antminer S21 family runs Bitmain's BM1368 and BM1370 chips on the CVitek CV1835 control board — and, unlike the S19 generation, it has no PIC microcontroller, so a "missing PIC" on an S21 board is normal, not a fault. The base S21 carries 108 BM1368 chips per board across 12 voltage domains; the S21 XP moves to 91 BM1370 chips across 13 domains for higher efficiency.

Bitmain documents each S21 variant on its own short, undated spec page with no decoder and no link between them. This is the owner's roof over all of it: every variant's real internals — chip, chips per board, voltage domains, control board, PSU — alongside the tuning, error-code, repair and lifecycle data the spec sheet leaves out. All figures are cross-checked against our Laval repair bench and the internal hardware reference.

Variant decoder — every Antminer S21 member, with the internals Bitmain never states

Model	Chip	Chips/board	Domains	Chips/domain	Hashrate	Power	Efficiency	Cooling	Control board	PSU
Antminer S21	BM1368	108	12	9	~195–200 TH/s	~3500 W	~17.5 J/TH	Air	CVitek CV1835	APW171215a
How to identify: Air-cooled chassis, no PIC on hashboard, EEPROM at U6. Notes: No PIC microcontroller (removed at the BM1368 generation). 11 level shifters added vs S19.
Antminer S21 Pro	BM1370	varies by bin	varies	varies	~234 TH/s	~3531 W	~15 J/TH	Air	CVitek CV1835	APW171215a
How to identify: Air-cooled, BM1370 silicon, no PIC. Higher rated TH/s sticker than base S21. Notes: BM1370 efficiency-class chip (same chip family as the S21 XP and Bitaxe Gamma).
Antminer S21 XP	BM1370	91	13	7	~270 TH/s	~3645 W	~13.5 J/TH	Air	CVitek CV1835	APW171215a
How to identify: 12 level shifters (U1–U12); temperature handled by U19 (4-way I2C switch), U20, U22. Notes: Domains 1–11 use 1.2 V / 0.8 V LDOs; domains 12–13 use MP2019 converters → 2.5 V → LDOs. Boost output ~21 V.
Antminer S21+	BM1370	varies	varies	varies	~216–235 TH/s	~3536 W	~15 J/TH	Air	CVitek CV1835	APW171215a
How to identify: Air-cooled "+" refresh of the S21 on BM1370 silicon. Notes: Same no-PIC architecture as the rest of the generation.
Antminer S21 Hyd / S21+ Hyd	BM1368 / BM1370	varies	varies	varies	~335–358 TH/s	~5360 W	~16 J/TH	Hydro (water)	CVitek CV1835	External hydro PSU
How to identify: Sealed water-cooling manifold; no fans on the chassis. Notes: Liquid-cooled SKUs run far higher absolute hashrate per unit; see the Hydro maintenance hub for coolant care.
Antminer S21 XP Hyd / S21e Hyd	BM1370	varies	varies	varies	~473–600 TH/s	~5676 W+	~12 J/TH	Hydro (water)	CVitek CV1835	External hydro PSU
How to identify: Highest-density water SKUs in the family; 3U immersion/hydro variants exist. Notes: Marketed efficiency improves with water cooling because the silicon runs cooler at the same clock.

Voltage is regulated per voltage domain, never per chip — a group of chips shares one regulated rail. Frequency and voltage targets are calculated at runtime by the autotuner; they are not fixed presets.

Owner data strip — tuning, errors, profiles, repair

S21 power-tuning data — wall-watt vs hashrate vs J/TH bands per model, with the safe under-volt envelope our bench validated — lives in the Power Profiles Database. Frequency and voltage are calculated at runtime by the autotuner; they are not fixed presets.

Power Profiles Database — wall-watt vs hashrate vs J/TH tuning bands.
Universal ASIC Spec Database — full per-SKU spec rows for every Antminer S21 variant.
ASIC Fault Finder — 650+ error codes, filterable by model and symptom.
Antminer S21 family hashboard repair
Antminer S21 error codes

Lifecycle — support, used market, and second life

Support / end-of-service: Current generation. No end-of-service notice; full Bitmain warranty and parts availability as of June 2026. Track future status on the EOS Tracker. Antminer EOS Tracker →

Used market: The S21 line holds the strongest used-market value of any current Antminer because of its efficiency. Condition (air vs hydro, hours, hashboard health) drives the price more than the sticker TH/s.

Heat reuse: At ~3.5 kW per unit an S21 is a serious space heater; the hydro SKUs are well suited to hydronic loops. See the heat-reuse hub before you decommission one.

Fix it — top failure modes and what they cost

Hashboard not detected / 0 of 3 boards — most often a domain fault or signal-chain break (CO→CI). Because there is no PIC, voltage enable is handled differently than on the S19; a "no PIC" reading is not the fault.
Boost-circuit failure on the ~25 V rail (U206 on the S21) — common across the S19/S21 boost design; replaceable as a pre-built boost module.
Low hashrate from one or more dead voltage domains — a single shorted chip pulls its domain low and can current-limit the whole board.
PSU over-current / power-cable melt on the APW171215a — verify connector seating and cable gauge before re-powering.

Flat-rate, transparent repair pricing (CAD) and the honest "when we will tell you NOT to repair" call: ASIC Repair Pricing → · Book an ASIC repair →

Get one — or get yours repaired

We are not Amazon. Miners are built to order and refurbished on our own Laval bench since 2016 — lead times are honest estimates, not promises.

Open firmware for the Antminer S21?

DCENT_OS is D-Central's closed beta open-source firmware (GPL-3.0, experimental firmware, not production-ready; it can brick your miner). For the Antminer S21 family it is in active development; ships last in the staged rollout. Waitlist only, never a pre-order. DCENT_OS beta status → It stands on the shoulders of the open community — Braiins (autotuning, Stratum V2), CGMiner, skot and OSMU.

Frequently asked questions

Does the Antminer S21 have a PIC chip?

No. The PIC microcontroller was removed at the BM1368 generation, so the S21, S21 Pro, S21 XP and S21+ have no PIC. A board that reads "no PIC" is behaving normally — voltage enable is handled by the control board and on-board regulators, not a PIC.

What chip is in the Antminer S21 vs the S21 XP?

The base S21 and S21 Hydro use the BM1368 (~17.5 J/TH class). The S21 Pro, S21 XP and S21+ use the more efficient BM1370 (~15 J/TH class) — the same chip family as the Bitaxe Gamma.

How many chips per hashboard does the S21 have?

The base S21 carries 108 BM1368 chips per board across 12 voltage domains (9 chips per domain). The S21 XP carries 91 BM1370 chips across 13 domains (7 chips per domain). Voltage is regulated per domain, never per chip.

Is the Antminer S21 still supported by Bitmain?

Yes — the S21 is the current generation with full warranty and parts as of June 2026. You can confirm any model's support status on our Antminer EOS Tracker.

Can you repair an Antminer S21 hashboard?

Yes. We diagnose and repair S21 / S21 Pro / S21 XP / T21 hashboards at the component level on our Laval bench — boost-circuit, domain and chip-level faults. See the S21 hashboard repair guide and our flat-rate repair pricing.

Related products, repair, and setup paths

Last reviewed June 13, 2026.