Why Mining Pool Centralization Has Become a Risk Again
Mining pool centralization is a risk again because hashrate is permanently consolidating across the three dimensions of geography, jurisdiction, and infrastructure in an unprecedented way. Foundry USA commands nearly 30% of the global hashrate, and the top two mining pools combined can already trigger a chain reorganization. The "old cycle" — miners shut down after losses, difficulty drops, survivors become profitable, hashrate recovers, and concentration dilutes — has been broken: the hashrate of exiting miners is being permanently sold to AI data centers and is not returning to the Bitcoin network.
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Why the risk has escalated: from "temporary concentration" to "permanent consolidation"
Historically, mining pool concentration was considered a short-term fluctuation that the market could self-correct. When hashrate became highly concentrated, it would automatically disperse due to increased competition and miners' concerns about centralization. The rapid recovery of Bitcoin after China's 2021 ban is a classic example of this resilience.
But the situation in 2026 is different. Hashrate is evolving from "temporary concentration" to "permanent consolidation" for three reasons:
The economic structure and the "old cycle" have been broken: The previous cycle was "miners in loss → shut down → difficulty drops → survivors profit → hashrate recovers → concentration dilutes." When the Bitcoin price stays below miners' all-in cost (around $80,000–$88,000) for a prolonged period and about 20% of miners can no longer sustain operations, this cycle is broken. These vulnerable miners who are forced out do not wait for a price rebound to restart. Their hashrate is permanently sold to AI hyperscalers that pay higher compensation, through three-year contracts. Once the hashrate leaves, it does not come back.
Direct pressure from regulation and compliance: Bitcoin was designed to be censorship-resistant, but the on-chain reality is different. In 2023, the mining pool F2Pool censored transactions based on the sanctions list of the U.S. Office of Foreign Assets Control (OFAC), only to reverse the decision after community backlash. Today, the top two mining pools (Foundry USA and AntPool) together control more than 55% of the hashrate, with Foundry being a U.S. entity and AntPool associated with China. Some analysts sharply note: "Just serve a subpoena to these two, and they will comply with any censorship regime."
Concentration of geographic and political influence: As of June 2026, the United States controls about 42.5% of the global hashrate, with U.S. publicly listed miners accounting for 31.5%. The real risk is not simply geographic concentration, but "concentration at the mining pool level". This is because mining pools hold key control over transaction inclusion and block template creation. Currently, the leading pools together control more than two-thirds of the hashrate, with transaction selection power highly concentrated.
51% attack risk: not absolute, but no longer theoretical
The combined hashrate of the top two mining pools (Foundry USA at roughly 30%–33%, and AntPool at roughly 17%–18%) has long exceeded or approached 51%. While there is a fundamental difference between two pools colluding to launch an attack and a single pool alone controlling 51%, Bitcoin's Nakamoto Coefficient (the minimum number of entities required to control more than 51% of the hashrate) has dropped to 3, which is a warning signal.
Even more noteworthy is an event in March 2024: Foundry mined seven consecutive blocks, triggering a two-block chain reorganization that caused AntPool and Viabtc chains to become "orphaned blocks." This was not an attack, but simply a mathematical consequence of hashrate concentration, clearly demonstrating the reality that a single entity can inadvertently dominate the network's history through pure hashrate advantage.
Three steps to verify current concentration
Check the Nakamoto Coefficient: Look up Bitcoin's "Nakamoto Coefficient" on a data analytics platform (such as Hashrate Index). Currently at 3, meaning only three entities need to collude to theoretically control the network.
Examine the mining pool hashrate distribution: Observe the dynamic hashrate shares of Foundry USA and AntPool. Watch for when each breaks the thresholds of 35% and 20%, respectively.
Monitor network difficulty adjustments: Over the past six weeks, Bitcoin hashrate has fallen by 20%, and difficulty just completed the 11th largest drop in history (-10.09%). This is direct evidence that microeconomic pressures are forcing vulnerable miners out.
The solution: Stratum V2 is a hope, but not a panacea
The only structural solution is the Stratum V2 protocol. Unlike the current Stratum V1, which delegates block construction to the mining pool, V2's "job negotiation" feature allows individual miners to build their own block templates, thereby taking transaction selection power away from the pool and weakening the pool's censorship capability. Although seven major pools, including AntPool, F2Pool, and Foundry, have joined the Stratum V2 working group, the core problem remains: it does nothing to address hashrate concentration, and it still has not achieved the adoption rate covering 75% of the network's hashrate.
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Ways to confirm completion
The current combined share of Foundry USA and AntPool — if it exceeds 55%, centralization risk is at a high level.
The trend of mining difficulty changes over the past 30 days — if it continues to fall significantly, vulnerable miners are being permanently eliminated.
Stratum V2 adoption rate — if it still hasn't improved notably, structural decentralization still requires patience.
Next step: If you are merely a user holding or trading BTC, changes in mining pool concentration will not affect your balance in the short term, but they increase the long-term risk of network transactions being interfered with. If you operate mining machines, you need to urgently evaluate whether there is still a profit margin at the current coin price and electricity cost, and consider joining a Stratum V2-supporting pool to retain more decision-making power. In the coming year, the biggest test for Bitcoin decentralization is not a technological breakthrough, but how to break the new cycle of "permanent hashrate consolidation."
