What we know about the U3S21EXPH

Earlier this month, Bitmain announced its latest hydro-cooled ASIC miner, the Antminer U3S21EXPH.

Besides being a mouthful to say (if anyone from Bitmain’s marketing department is reading this, hit us up – we have some ideas), the miner is the most powerful and efficient Antminer ASIC to date. It features Bitmain’s first-ever server rack form factor that bucks the shoebox miner standard that has defined ASIC miners for the last decade, and it was developed in a partnership with Hut 8. 

There isn’t too much information floating around on this hydro-cooled model, but for today’s newsletter, we’ve pieced together what we can.

Here’s what we know. 

Antminer U3S21EXPH is a step forward in hashrate, efficiency, and form factor

The Antminer U3S21EXPH is the most powerful and efficient ASIC miner on the market, and these feats are largely a result of the miner’s server rack design. 

Traditionally, ASIC miners have been built in a shoe box design: an aluminum box houses the hashboards and a control board, and an external power supply unit (PSU) feeds the miner the juice it needs to run. If the model is aircooled, it comes complete with fans, but if it’s hydro cooled, it typically features straw-like tubes that circulate water through the machine to keep it cool.

For the U3S21EXPH, Bitmain scrapped the shoebox design in favor of a server-rack design, something that professional bitcoin miners have long asked for. Another first, the U3S21EXPH also uses direct liquid-to-chip cooling, a common standard for liquid-cooled HPC data centers. 

The new design packs multiple units on a single rack, endowing the U3S21EXPH with its impressive 860 TH/s hashrate, and the direct liquid-to-chip cooling design allows it to press the boundaries of efficiency at 13 J/TH. In a conversation with Blockspace, Brad Cuddy, the director of energy operations at Cholla Energy, postulated that the “U3” in the unit’s name is a bit of wordplay on Bitmain’s part – an inversion of “3U,” the server rack mount specification that the U3S21EXPH fits. 

Cuddy, who operates hydro-cooled ASIC miners for Cholla, told Blockspace that “he’s excited to see the shift from the shoebox design to the [server rack] form factor.” However, the U3S21EXPH’s voltage range limits its compatibility with some of the hardware and electrical infrastructure that bitcoin miners use for various Bitmain and MicroBT models, he continued.

“The restricted range of 380 to 415 volts reduces its compatibility for retrofitting. I would have liked to see the voltage range go all the way up to 480 volts to allow for more interoperability with current infrastructure deployments.”

As a result, the new model precludes bitcoin miners from using certain transformers that they have already deployed for existing mining operations. Specifically, Cuddy mentioned that the U3S21EXPH would be incompatible with mines that are running 3-phase powered Whatsminers like the M63 and M66 series at 480 volts. It would also be incompatible “with any transformer providing 277 volts to single phase air-cooled units,” he added.

Bitmain partnered with Hut 8 to develop the U3S21EXPH

In what appears to be a first for Bitmain, the ASIC manufacturer partnered with a public bitcoin miner, Hut 8, to develop the U3S21EXPH. 

Hut 8 has “developed a custom design for Bitcoin mining data center infrastructure inspired by traditional rack-based architecture,” the miner stated in its press release about the partnership. Hut 8 had a hand in formulating this server rack design (a “U form factor,” as it is commonly called in the traditional data center world), according to Sue Ennis, Hut 8’s head of investor relations. 

“Hut 8 was instrumental in the custom design for the infrastructure, particularly the U form factor which is compatible with HPC style architecture.”

Hut 8 believes that liquid cooling is the future of data center heat management, she continued, citing that 40% of data centers could use liquid cooling by 2026, according to estimates by data center developer and operator Cyrus One. The U3S21EXPH’s direct liquid-to-chip cooling design should help these units maintain better power efficiency while also achieving a power density per rack of roughly 180kW.

Per its partnership, Hut 8 will host 15 EH/s of the U3S21EXPH for Bitmain. The company will have the option to purchase all or part of this deployment at a fixed price in up to three tranches within six months of each respective installment’s energization. 

Should Hut 8 purchase the entire fleet, it would increase its hashrate from 5.6 EH/s to 20.6 EH/s, and if it doesn’t purchase any units, the hosting agreement will still increase Hut 8’s hashrate under management from 18.5 EH/s to 33.5 EH/s.

U3S21EXPH price and shipping dates

According to an order notice shared with Blockspace, the Antminer U3S21EXPH’s initial price is $30.7/TH ($26,402 per unit) before coupon or $21.49/TH ($18,481 per unit) with a coupon. (Bitmain often provides promotional coupons to wholesale customers and miners during a new release). For bulk purchases, Bitmain is accepting 20% payment upfront, 30% “medium term payment” and a 50% final payment upon delivery.

Per the product sheet, Bitmain plans to begin shipping the U3S21EXPH in November and December of this year.