Bitmain's Antminer S21 Hydro (335TH): Full Hardware Overview

Bitmain refreshed the Antminer S21 Hydro on January 2, 2025, bumping hashrate from the original 330 TH/s to 335 TH/s while holding 16.0 J/TH efficiency. It's a minor refresh on paper, but it kicks off a wave of S21 hydro releases that would expand the lineup three more times over the following months.

TLDR

• Minor hashrate refresh: 330 TH/s → 335 TH/s (+1.5%), efficiency unchanged at 16.0 J/TH. Any new S21 Hydro order from January 2025 onwards ships in the 335 TH/s configuration.
• Breakeven electricity cost: ~$0.146/kWh at ~$56/PH/day hashprice (early January 2025). Positive margin across the full $0.04–$0.12/kWh industrial range.
• Entry-level hydro option in the S21 generation — at launch of the 335 TH/s refresh, the only other hydro variant was the S21 XP Hydro at 12.0 J/TH. The S21+ Hydro and S21e Hydro arrived in the following weeks.
• Sits in the sub-19 J/TH top revenue-per-watt tier with a 3 J/TH buffer below the tier boundary.
• LuxOS autotuning available — underclocking can partially close the J/TH gap to the higher-tier XP Hydro.

Background

The original Antminer S21 Hydro launched alongside the S21 air-cooled in late 2023, shipping at 330 TH/s and 16.0 J/TH. For over a year, it remained the only hydro variant of the S21 generation — until June 2024, when the S21 XP Hydro arrived with a major efficiency jump to 12.0 J/TH at 473 TH/s. Six months later, on January 2, 2025, Bitmain refreshed the base S21 Hydro to 335 TH/s.

The 335 TH/s update is a modest 1.5% hashrate gain over the original 330 TH/s variant, with no change to efficiency. For buyers, the practical implication is simple: any new S21 Hydro order from January 2025 onwards ships in the 335 TH/s configuration. Secondary market units may still be either spec depending on production batch.

Antminer S21 Hydro (335TH) Specifications

Where the S21 Hydro (335TH) Sits in the S21 Hydro Lineup

The S21 hydro stack as of early January 2025:

At launch of the 335 TH/s refresh, the S21 hydro lineup had only two variants. The S21 XP Hydro held the efficiency crown at 12.0 J/TH, while the refreshed S21 Hydro served as the entry-level hydro option at 16.0 J/TH. The S21+ Hydro (Feb 2025) and S21e Hydro (Apr 2025) would arrive over the following weeks to fill out the mid-tier.

Hashcost Breakeven Analysis

USD hashprice was trading in the $55–$60/PH/day range in early January 2025 — $55.00 on December 30, 2024, climbing to $59.28 by January 6, 2025 per HRI roundups. The table below uses ~$56/PH/day as the launch-window anchor.

Based on ~$56/PH/day USD hashprice (Luxor Hashprice Index, early January 2025). Calculated using S21 Hydro (335TH) nameplate specs: 335 TH/s, 5,360 W (128.64 kWh/day). Breakeven electricity cost approximately $0.146/kWh.

Breakeven electricity cost at this hashprice sits at approximately $0.146/kWh. The S21 Hydro (335TH) generates positive margin across the full $0.04–$0.12/kWh range that covers most industrial operators. Margins tighten meaningfully above $0.13/kWh.

Fleet Efficiency Context

At 16.0 J/TH, the S21 Hydro (335TH) sits in the sub-19 J/TH top revenue-per-watt tier on Luxor's Energy Hashprice Index. The 3 J/TH buffer below the tier boundary gives this model durable margin advantage over the broader fleet — though less than the S21 XP Hydro's 12.0 J/TH offers. For operators choosing between the two hydro variants, the question becomes whether the efficiency premium of the XP is worth its higher acquisition cost.

LuxOS Firmware Compatibility

LuxOS — Luxor's proprietary firmware for Bitmain Antminers — supports the S21 series including the S21 Hydro. For the 335 TH/s variant specifically, LuxOS autotuning provides a path to further efficiency gains through underclocking, partially closing the J/TH gap to the higher-tier XP Hydro.

Explore LuxOS at luxor.tech/firmware.

Who Should Buy the S21 Hydro (335TH)?

• Operators with hydro infrastructure looking for the most affordable hydro entry point in the S21 generation.
• Buyers who don't need the absolute peak efficiency of the S21 XP Hydro but want the operational benefits of hydro cooling — quieter operation, denser per-TH footprint, tighter clock control.
• Miners with sub-$0.08/kWh power who can absorb the efficiency gap to XP-tier hydro models in exchange for lower acquisition cost.
• Operators running LuxOS who can autotune to recover additional efficiency on the 335 TH/s chassis.

Where to Buy

For S21 Hydro pricing, availability, and fleet-scale orders, reach out to Luxor's hardware trading desk via luxor.tech/hardware. Luxor's desk handles both single-unit and bulk institutional orders.

For live hashprice, real-time profitability calculations, and the latest ASIC market data, visit hashrateindex.com.

About Luxor Technology

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. Nothing contained in our content constitutes a solicitation, recommendation, endorsement, or offer by Luxor or any of Luxor's employees to buy or sell any derivatives or other financial instruments in this or in any other jurisdiction in which such solicitation or offer would be unlawful under the derivatives laws of such jurisdiction.