BM1370: The ASIC Chip That Brought Home Mining Back
Werner BundschuhShare
If you own a Bitaxe Gamma, a NerdQaxe++ or a BitForge Nano, there is a small piece of silicon inside that was originally designed for very different machines: the BM1370. Bitmain developed it for the industrial Antminer S21 Pro, which runs in large numbers in mining farms with megawatt power connections. The fact that the same chip now works on your desk is the result of years of reverse-engineering work by the open-source mining community.
This article explains what the BM1370 can do, where it comes from and why it has become so important for home miners. Where figures are not officially confirmed, we say so.
The BM1370 is a SHA-256 mining ASIC made by Bitmain. It is considered a 5 nm class chip, probably manufactured by TSMC; Bitmain has not officially confirmed this. A single chip delivers 1.0 to 1.2 TH/s at around 18 W (about 15 J/TH) at stock settings. In the Antminer S21 Pro, 252 of them work in parallel to produce 234 TH/s at 3,531 W. In the open-source world, the same chip powers compact home miners: one in the Bitaxe Gamma, two in the Bitaxe GT and the BitForge Nano, four in the NerdQaxe++. With good cooling it can be overclocked to over 2 TH/s per chip, which is considerably more headroom than the older chips used in earlier Bitaxe models.
The Story: How an Industrial Chip Ended Up on Your Desk
To understand the BM1370, it helps to look at the Bitaxe project. Skot9000, real name Skot Croshere, is an electrical engineer and Bitcoiner. In early 2023 he asked himself whether the ASIC chips from Bitmain's industrial miners could be put on a simple, open board that anyone could run at home.
The problem: Bitmain publishes no datasheets for its ASICs. There are no register maps, no description of the communication protocols and no official specifications. Anyone who wants to drive a BM1397, BM1366, BM1368 or BM1370 starts from scratch.
That is exactly what Skot did. Over several years he took Bitmain hardware apart, captured the communication between controller and ASIC with an oscilloscope, measured voltages and reconstructed, step by step, how each new chip works. That knowledge now lives in the ESP-Miner firmware (better known as AxeOS), the open-source driver for the entire Bitaxe family.
The Bitaxe generations follow Bitmain's chip history directly:
- Bitaxe Max (2023): BM1397 from the Antminer S17, approx. 400 GH/s
- Bitaxe Ultra (2023): BM1366 from the S19 XP, approx. 500 GH/s
- Bitaxe Supra (2024): BM1368 from the S21, approx. 625 to 775 GH/s
- Bitaxe Gamma (August 2024): BM1370 from the S21 Pro, 1.0 to 1.2 TH/s
On August 19, 2024, Skot posted on X: "The bitaxeGamma is go! The newest member in the #bitaxe lineup features the BM1370 ASIC from the Antminer S21 Pro. So far we've been able to pull 1-1.2 TH/s at around 15 J/TH from a single chip". For the first time there were home miners with terahash-class performance at under 20 watts, something that had not seemed within reach just a few months earlier.
What the BM1370 Is, Technically
The BM1370 is an Application-Specific Integrated Circuit (ASIC), a chip built for exactly one task: computing SHA-256 hashes. That is what Bitcoin mining comes down to at the hardware level. A 256-bit number is computed from a block header in the hope of finding one below the current difficulty target.
Unlike the processor in your computer, a BM1370 cannot process text or render web pages. It does its one job massively in parallel, with an efficiency that exceeds a GPU by a factor of 60 or more.
Specifications at a Glance
| Parameter | Value |
|---|---|
| Hashrate (stock) | 1.0 to 1.2 TH/s per chip |
| Efficiency (stock) | ~15 J/TH |
| Power consumption (stock) | ~15 to 18 W per chip |
| Manufacturing process | 5 nm class (TSMC, not officially confirmed) |
| Algorithm | SHA-256 (double hash) |
| Voltage (typical) | 1.15 to 1.25 V core voltage |
| Frequency (stock) | ~525 MHz |
| Frequency (overclocking ceiling) | 900 to 1,000 MHz (with adequate cooling) |
| Package | BGA with 300+ solder balls (micro-BGA) |
A note on the manufacturing process: Bitmain does not officially state the exact node. The mining industry generally gives 5 nm for the BM1370 family. Its predecessors, the BM1366 and BM1368, are considered to use the same or a very similar process. On that basis, the BM1370 differs from them mainly through a more efficient design rather than a smaller node.
The Chip Family: Not Every BM1370 Is the Same
There are several variants under the name "BM1370". Zeus Mining and other repair specialists list at least six versions: BM1370AA, BM1370BB, BM1370BC, BM1370PA, BM1370PB and BM1370PF. Bitmain does not explain what the letters mean. The community often assumes they stand for different test grades from a process called speed binning. They could just as well refer to revisions or production batches; none of this is confirmed.
Speed binning is common practice in semiconductor manufacturing. Even within the same wafer lot, individual dies behave slightly differently. Some run stable at lower voltage, others need more; some reach 1,000 MHz, others top out at 750 MHz. Manufacturers test chips after production and sort them into performance grades. For Bitmain, the community assumes the following split, which the manufacturer itself has not confirmed:
- chips with the best efficiency go into models like the S21 Pro
- middle grades go into standard S21 models
- lower grades go to the repair market and, through third parties, sometimes into open-source boards
What is certain is that individual chips differ. The community calls this the "silicon lottery": two Bitaxe Gamma units that look identical can behave quite differently when overclocked. One runs stable at 1.8 TH/s, the other becomes unstable at 1.5 TH/s. That is why experienced miners always share their overclocking settings with the caveat "your mileage may vary".
Where the BM1370 Is Used
In Industry
Bitmain's Antminer S21 Pro was the first device to use the BM1370 and is considered the model that contains most of these chips. One unit carries 252 chips on three hashboards and reaches 234 TH/s at 3,531 W, which works out to 15.1 J/TH. When it was released in 2024, the S21 Pro was among the most efficient industrial miners on the market.
Later models such as the S21 XP, the S21+ and the S21 XP Hydro use variants of the same BM1370, some with water cooling for higher clock speeds and correspondingly more hashrate per unit.
In Open-Source Hardware
Here the designs are publicly available:
- Bitaxe Gamma: one BM1370, 1.0 to 1.2 TH/s, ~17 to 18 W. The direct successor to the Bitaxe Supra line, designed by Skot himself.
- Bitaxe GT (801): two BM1370 chips on a 6-layer PCB, ~2.4 to 2.6 TH/s, ~43 W. Skot's own dual-chip design.
- BitForge Nano: also two BM1370 chips, 2.4 to 2.6 TH/s, ~36 W at factory settings. Its own enclosure and ForgeOS firmware, developed in Germany.
- NerdQaxe++: four BM1370 chips, around 4.9 TH/s at around 75 W. Currently our flagship: S21 Pro efficiency in a desktop format, Made in Germany.
- NerdOctaxe Gamma: eight BM1370 chips, ~8 TH/s at ~160 W. One of the largest fully open single-board designs.
- Bitaxe Gamma Hex: six BM1370 chips, over 6 TH/s
All of these devices share the same chip, the same open-source driver and the same reverse-engineering origin. They differ in the number of chips, the PCB layout, the power delivery and the cooling.
Overclocking: The Real Potential
A notable property of the BM1370 is its overclocking headroom. Older BM1366 and BM1368 chips hit thermal limits at 550 to 600 MHz. Many BM1370 units, by contrast, run stable at 900 to 1,000 MHz, but only with significantly better cooling.
Community results:
- stock (525 MHz / 1150 mV): 1.07 TH/s at around 17 to 18 W
- moderate overclock (700 MHz / 1200 mV): ~1.4 TH/s at ~15 W
- aggressive overclock (900 MHz / 1250 mV): ~1.84 TH/s at ~25 W
- with very good cooling: over 2 TH/s from a single chip
Power draw rises faster than the hashrate when overclocking, so efficiency in J/TH gets worse. The probability of finding a block rises in the same proportion as the hashrate. For lottery mining, a moderate overclock often gives the best ratio of electricity cost to block chance.
Important: Overclocking requires better cooling. The included stock heatsink usually only supports up to ~700 MHz. For higher frequencies, larger heatsinks (pin-fin designs, bigger fans) or, on multi-chip boards, water cooling make sense.
Block Finds with BM1370 Hardware
Since the BM1370 was released, these Bitcoin blocks found by open-source hardware with this chip have been documented:
- March 2025, block #889,975: A Bitaxe Gamma at stock settings with 1.2 TH/s finds a block. Payout: 3.149 BTC.
- September 5, 2025, block #913,272: first documented block find with a NerdQaxe++ (4.8 TH/s), via the Ocean pool with DATUM.
- October 27, 2025, block #920,440: A home setup with six NerdQaxe++ units finds a block; the payout was worth around $342,000.
Statistically these are outliers. The daily probability, even for a NerdQaxe++ cluster, is in the range of one in millions. The protocol, however, makes no distinction between 234 TH/s and 1.2 TH/s: a valid hash is a valid hash.
What the BM1370 Is Not
A few misconceptions circulate online that are worth correcting:
"The BM1370 is manufactured on a 7 nm process." That is considered unlikely. Experts regard 15 J/TH as hardly achievable on 7 nm; the BM1366, which is considered a 5 nm chip, was already well above that. Bitmain confirms nothing officially, but the industry places the BM1370 in the 5 nm class.
"Mining ASICs validate transactions." Wrong. Transactions are validated by Bitcoin nodes (e.g. Bitcoin Core). The BM1370 only computes SHA-256 hashes on a prepared block header. If you want to mine without trusting third parties, you also need your own full node.
"Open source means the chip is open." Wrong. The BM1370 itself is proprietary Bitmain hardware. What is open is everything Skot and the community built around it: PCB layouts, the ESP-Miner/AxeOS firmware, drivers and schematics. The chip remains a black box, but reverse engineering has documented its behavior to a large extent.
"With a Bitaxe Gamma you'll find a block every few weeks." Very clearly wrong. The mathematical probability per block is roughly 1 in 670 million. If you buy with that expectation, you will be disappointed. If you buy out of conviction, for decentralization, for learning or as a hobby, you are in the right place.
Comparison with Its Predecessors
| Chip | Source | Hashrate (per chip) | Efficiency | Bitaxe Model |
|---|---|---|---|---|
| BM1397 | Antminer S17 | ~400 GH/s | ~40 J/TH | Bitaxe Max |
| BM1366 | Antminer S19 XP | ~500 GH/s | ~20 to 25 J/TH | Bitaxe Ultra / Hex |
| BM1368 | Antminer S21 | 625 to 775 GH/s | ~17 J/TH | Bitaxe Supra |
| BM1370 | Antminer S21 Pro | 1.0 to 1.2 TH/s | ~15 J/TH | Bitaxe Gamma / GT, BitForge Nano, NerdQaxe++ |
From the BM1397 to the BM1370, hashrate per chip has roughly tripled, and efficiency has improved by a factor of about 2.5. Three years of mining hardware development, made traceable through open-source reverse engineering.
FAQ
Can I buy individual BM1370 chips?
Yes, with limitations. Suppliers such as TinyChipHub (a maker of Bitaxe devices), Zeus Mining or Bitmars sell individual chips from about $15 to $25 each. Zeus Mining and Bitmars mainly sell replacement chips for defective S21 Pro hashboards. Important: Installation requires a BGA rework station, a reflow oven with precise temperature control and ESD protection. A hot-air gun will not do the job. Even experienced technicians report failure rates above 40% on BGA swaps.
Why Does the BM1370 Work Well in Open-Source Boards If They Are Not Supposed to Get Top Chips?
Whether open-source boards actually receive lower grades is not confirmed (see above). Even if they do, a chip that is slightly worse than the best ones in the S21 Pro is still very efficient. The community estimates the difference between good and average units at typically 5 to 10%. For home mining with a lottery character this hardly matters, because electricity costs are only a few euros per month anyway.
How Many BM1370 Chips Have Been Produced?
Bitmain does not publish exact figures. A rough estimate: with 252 chips per S21 Pro and several hundred thousand industrial units produced, the total is likely over 100 million chips. Only a small single-digit percentage of these ends up in the open-source market.
What Is the Successor to the BM1370?
The industry talks about an upcoming BM1372 or BM1380 on a 3 nm process with a target efficiency below 12 J/TH; Bitmain has not confirmed this. Competitors such as Auradine (AT2880) and Block (Proto, Jack Dorsey's mining project) are also developing 3 nm chips. Open-source Bitaxe hardware with such chips is unlikely to arrive before late 2026, once Skot and the OSMU community have reverse-engineered the respective chip.
Does the ESP-Miner Firmware Work with All BM1370 Variants?
Based on community experience, essentially yes. The Bitaxe firmware runs with the common BM1370 variants (BB, BC, AA, PA, PB). Initialization and the Stratum protocol are the same for all of them. Differences show up when overclocking and in thermal behavior.
Conclusion: Why the BM1370 Matters
The BM1370 is the result of a long chain. Bitmain invests hundreds of millions of dollars in an ASIC for industrial mining farms. Skot9000 and Open Source Miners United put thousands of hours into reverse engineering. Manufacturers such as TinyChipHub, D-Central, BitForge and Solomining build hardware on top of it that you can put on your desk.
A single person with a Bitaxe Gamma costing €200 to €300 therefore has a real, if vanishingly small, chance of finding an entire Bitcoin block, currently worth around $280,000 to $340,000. That chance is not zero. The Bitcoin protocol makes no distinction between a 234 TH/s industrial machine and a 1.2 TH/s home miner.
The BM1370 has brought that within reach of home miners again.
BM1370 hardware directly from us:
- Bitaxe 603 Gamma: one BM1370 at 1.54 TH/s out of the box with the Copperzilla 2.0 in black aluminium
- NerdQaxe++ Made in Germany: our flagship with four BM1370 chips (around 4.9 TH/s, around 75 W)
Questions about the BM1370, overclocking, cooling or the right hardware for your setup? Get in touch, we know the chip first-hand.
Sources: Bitaxe Gamma GitHub, Skot9000 (X), Bitcoin Magazine, D-Central: ASIC Fabrication, D-Central: Bitaxe Overclocking Guide, DTV Electronics: BM1370 ASIC Chip. As of May 2026.