Antminer S9 vs S21: Which ASIC Miner Wins in 2025?

When it comes to Bitcoin mining, the process of validating transactions and securing the Bitcoin network using specialized hardware. Also known as Proof of Work mining, it's the backbone of Bitcoin’s security and has evolved dramatically since 2013. The two most talked-about machines in this space are the Antminer S9, a 2016-era ASIC miner that dominated the market for years and the Antminer S21, Bitmain’s 2024 flagship miner built for today’s high-difficulty network. These aren’t just upgrades—they’re from different eras, with different power needs, profits, and risks.

Let’s cut through the noise. The S9 runs on 14nm chips, pulls 1,375 watts, and hashes at 14 TH/s. It’s loud, hot, and eats electricity like a furnace. Back in 2018, it was profitable. Today? Most users run it only as a learning tool or in places with near-free power. Meanwhile, the S21 uses 5nm technology, hits 200 TH/s, and only draws 3,360 watts. That’s 14 times more power with less than triple the energy cost. If you’re mining seriously in 2025, the S9 is a relic. But here’s the catch: S21s cost $4,000–$6,000 new. The S9? You can buy one used for $100–$300. So if you’re on a budget, have cheap electricity, and don’t mind the noise, the S9 can still run. But if you want to make money, not just keep a museum piece alive, the S21 is the only real choice.

There’s also the matter of ASIC miner efficiency, how much hash power you get per watt of electricity. The S9 delivers about 0.1 TH/W. The S21 hits 59.5 TH/W. That’s a 600x improvement. That’s not an upgrade—it’s a revolution. Mining isn’t just about buying hardware anymore. It’s about energy costs, cooling, location, and uptime. The S9 can’t compete on any of these fronts today. Even if you find a warehouse with $0.03/kWh power, the S21 will still outearn it by miles.

And don’t forget maintenance. S9s are old. Fans fail. Power supplies die. Heat cracks the boards. You’ll spend more time fixing it than mining. The S21? It’s built for 24/7 operation with better thermal design and firmware support. Bitmain still releases updates for it. No one supports the S9 anymore.

So who should buy what? If you’re just curious, or you’ve got a garage with free power and nothing to lose, the S9 is a fun project. But if you’re serious about mining Bitcoin in 2025, the Antminer S21 is the only machine that makes sense. Everything else is just noise.