Bitcoin’s mining network crossed 1 zettahash per second sometime in mid-2026, and the number deserves more attention than it got. One zettahash is 10²¹ hash operations per second - a figure that would have been unimaginable during the GPU mining era and still strains comprehension today. For context, the network sat around 400 exahashes per second at the start of 2023. It has more than doubled in roughly three years.
The immediate consequence is that a 51% attack on Bitcoin has never been more expensive to execute. The cost isn’t just hardware - it’s the sustained energy expenditure required to outpace a distributed pool of miners whose collective investment runs into the tens of billions of dollars. At current difficulty levels, acquiring enough mining capacity to threaten the chain would require not just capital but lead time that makes surprise attacks essentially impossible.
What’s Driving the Expansion
The April 2024 halving cut the block subsidy to 3.125 BTC. Conventional wisdom at the time held that reduced rewards would squeeze miners with higher operating costs out of the market, compressing hashrate. That didn’t happen - or rather, it happened briefly and then reversed sharply. Miners who survived the subsidy cut were the more efficient operators, running next-generation ASICs, often in jurisdictions with cheaper power. The weak hands exited; the infrastructure they left behind was absorbed or replaced by better-capitalized entrants.
The post-halving Bitcoin price appreciation also mattered. Higher BTC prices denominated in fiat restore miner margins even when the per-block subsidy falls in BTC terms. Mining economics are always a product of both variables, not just the subsidy schedule.
The Fee Question That Still Doesn’t Have an Answer
Here’s the part nobody wants to sit with: block subsidies will eventually approach zero. The long-run security model depends on transaction fees filling that gap. Right now, fees are insufficient to sustain a 1-zettahash network without subsidy support - that’s not a controversial claim, it’s arithmetic. Ordinals and Runes activity has added fee revenue at the margin, but nothing close to replacing subsidy income.
The 1-zettahash milestone is genuinely impressive. It’s also a reminder that Bitcoin’s security model has a structural question baked into it that higher hashrate doesn’t resolve - it just defers.