Introduction

In this post, we cover the key specs, efficiency profile, and market positioning of Bitmain's Antminer S21 Pro — one of the most efficient air-cooled SHA-256 miners available on the secondary market today.

TLDR

Antminer S21 Pro At A Glance

• Manufacturer: Bitmain
• Series: Antminer S21
• Release Date: March–April 2024
• Algorithm: SHA-256 (Bitcoin)
• Cooling: Air-cooled
• Efficiency: 15.0 J/TH across all variants

Models

Background

The S21 Pro is part of Bitmain's S21 generation, launched in late 2023 and expanded through Q1 2024. It sits above the base S21 (200 TH/s | 17.5 J/TH) in both hashrate and efficiency, making it a meaningful step up for operators evaluating fleet upgrades. The S21 Pro family shipped in three hashrate configurations — 220, 234, and 245 TH/s — all sharing the same nameplate efficiency of 15.0 J/TH.

Specifications

Hashrate

The S21 Pro ships in three variants: 220, 234, and 245 TH/s. The 234 TH/s is the most common configuration on the secondary market. At 245 TH/s, it is one of the highest-hashrate air-cooled machines in Bitmain's S21 generation.

Efficiency

All three S21 Pro variants share a 15.0 J/TH efficiency rating — consistent across the lineup regardless of hashrate tier. This makes the S21 Pro notably more efficient than the base S21 (17.5 J/TH) and positions it competitively against other next-generation air-cooled machines on the market.

Efficiency comparison against prior Bitmain generations:

Power Draw

The S21 Pro draws between 3,300W (220T) and 3,675W (245T). Operators running dense racks should plan for approximately 3.5–3.7 kW per unit at nameplate and verify PDU ratings before deployment.

Cooling

Like all current air-cooled Antminers, the S21 Pro uses a dual high-speed axial fan configuration. The machine requires adequate facility airflow — either a hot-aisle/cold-aisle container setup or equivalent — to maintain stable operating temperatures.

LuxOS Firmware & Profitability

The S21 Pro is compatible with LuxOS, Luxor's custom ASIC firmware. LuxOS enables operators to run the machine across a range of underclocked and overclocked profiles, with Autotuner identifying the optimal voltage-frequency curve for each individual unit.

According to Hashrate Index's firmware efficiency testing, underclocking the S21 Pro to the -4 step (496 MHz) drops power draw to ~2,525W while sustaining approximately 199.8 TH/s — an efficiency gain of 18.67% over the stock 15.0 J/TH nameplate, reaching approximately 12.6 J/TH. That puts LuxOS-optimized S21 Pros in efficiency territory that competes with machines that launched at significantly higher price points.

Use Hashrate Index's Bitcoin Mining Profitability Calculator to model S21 Pro returns at your specific electricity cost and current hashprice.

How to Buy the Antminer S21 Pro

The S21 Pro is available on the secondary market through ASIC brokers. Luxor's ASIC Trading Desk sources S21 Pro inventory across all three hashrate configurations — 220, 234, and 245 TH/s.

For current pricing and availability, contact Luxor's hardware team directly:

[email protected]

Luxor's trading desk works with operators at all fleet sizes — from single-unit buyers to bulk institutional orders.

Final Take

The Antminer S21 Pro occupies a strong position in the current secondary market. Its 15.0 J/TH efficiency represents a meaningful upgrade over prior Antminer generations, and secondary market pricing well below 2024 launch levels improves the economics for operators evaluating fleet refreshes.

For operators who want to push efficiency further, LuxOS unlocks an additional 18%+ gain through underclocking — making the S21 Pro one of the stronger candidates for firmware optimization in Bitmain's current lineup.

Track live profitability and pricing per model:

• S21 Pro 220T — Hashrate Index
• S21 Pro 234T — Hashrate Index
• S21 Pro 245T — Hashrate Index
• Bitcoin Mining Profitability Calculator

To buy: [email protected]

About Luxor Technology Corporation 

Luxor delivers hardware, software, and financial services that power the global compute and energy industry. Its product suite spans Bitcoin Mining Pools, ASIC Firmware, Hardware trading, Hashrate Derivatives, Energy services, a Miner Management software, Commander, and a bitcoin mining data platform, Hashrate Index.

Disclaimer

This content is for informational purposes only, you should not construe any such information or other material as legal, investment, financial, or other advice.