51% Attack Risk Rises as Bitcoin Mining Centralizes

Key Points

• Foundry and AntPool now control over 51% of Bitcoin’s hashrate
• Experts warn this could enable a dangerous 51% attack
• Mining centralization reaches levels not seen in over a decade
• Trust in Bitcoin’s decentralization and PoW system is under threat

Bitcoin, once hailed as the backbone of decentralized finance, is now at a crossroads. Two mining giants, Foundry and AntPool, currently control more than 51% of the total hashrate, raising red flags across the crypto industry.

This has sparked growing fears that the network is becoming vulnerable to a 51% attack, a scenario where a majority miner can manipulate the blockchain.

Two Bitcoin mining pools now control over 51% of the network. The door is wide open for a 51% attack, which could completely destroy BTC.

For context, the last and only time this happened was 11 years ago, in 2014, with GHash,io. They had to voluntarily reduce their hashrate to… pic.twitter.com/SMLpVrGGdG

— Jacob King (@JacobKinge) August 19, 2025

According to on-chain analyst Jacob King, Foundry commands around 33.63%, while AntPool holds 17.94% of Bitcoin’s mining power. Combined, their influence exceeds the 51% mark, meaning that if these two entities ever chose to collaborate or were compromised, they could theoretically take control of the Bitcoin network.

Market share of Bitcoin mining pools. Source: Jacob King on X – Techtoken

This level of control could allow them to block transactions, reverse confirmed transfers, and even enable double spending, undermining trust in the entire system.

“Once reality sets in about how centralized, manipulated, and useless Bitcoin truly is, everything will collapse faster than ever,” King said. “It’s essentially a giant game of musical chairs!”

The centralization issue doesn’t stop there. According to researcher Evan Van Ness, three mining pools often hold over 80% of the global Bitcoin hashrate, which signals an even deeper centralization problem that’s hard to ignore.

Top 3 pools holding more than 80% of the hashrate. Source: Evan Van Ness on X – Techtoken

For a network that was supposed to be trustless and distributed, the latest mining data is a wake-up call. These developments follow a growing list of market shifts, such as the Ethereum whales selling during recent volatility, signaling broader investor caution across top chains.

Even Bitcoiners recognize that mining has become “highly centralized”

3 pools routinely have more than 80% of Btc hashrate

PoW is too centralized to be the backbone of the financial system

This is why ETH switched to PoS 🚀 https://t.co/Kg4PXfTHWa pic.twitter.com/m2xCh5OCGo

— Evan Van Ness 🧉 (@evan_van_ness) August 19, 2025

Why the 51% Attack Risk Is a Bigger Problem Than You Think

A 51% attack isn’t just a theoretical concern; it’s a known weakness of the Proof-of-Work (PoW) mechanism when mining power becomes too concentrated. In this attack, the entity controlling over half of the hashrate could:

• Censor or halt transactions

• Reorganize the blockchain to reverse transactions

• Double-spend coins

• Undermine network security

While the economic and technical costs of pulling off a 51% attack on Bitcoin are massive, the fact that it’s mathematically possible right now is what has investors rattled.

Mining infrastructure requires massive investment in specialized hardware, physical facilities, and enormous energy consumption.

An actual attack would likely crash Bitcoin’s price, hurting the attackers themselves. That’s why most analysts believe such an attack is unlikely, but not impossible.

Bitcoin just became a major risk and liability. pic.twitter.com/EdC3JOOPif

— DOQ (@doqholliday) August 19, 2025

The greater danger may lie in perception. Bitcoin is marketed as a decentralized, trustless network. If users and investors start questioning that narrative, the entire value proposition could weaken.

This could result in slower adoption, tighter regulations, and a dip in institutional confidence, similar to the market uncertainty during the Jackson Hole Bitcoin rally, where macro sentiment dictated price action.

And that confidence is key. As institutional interest in crypto grows, the idea that a small group of players could control and potentially manipulate Bitcoin might make institutions think twice before investing.

This is especially relevant following events like the SEC’s investigation into Alt5 Sigma, which reminded the market how quickly institutional perception can shift.

Bitcoin difficulty. Source: Blockchain.com – Techtoken

The Bigger Threat: Fear, Uncertainty, and Market Reaction

The crypto market isn’t just driven by numbers; it’s powered by emotion and belief. Fear, uncertainty, and doubt (often called FUD) can crash markets faster than fundamentals. And the current centralization of Bitcoin mining is creating exactly that.

Even though no 51% attack has occurred, the mere possibility has triggered widespread concern among both retail and institutional investors.

Bitcoin’s reputation as “digital gold” is built on the assumption that no single entity can control it. That image is now under pressure.

Several leading voices in the crypto community have called the situation “extremely centralized” and potentially damaging. This is the first time in over a decade that Bitcoin mining concentration has reached this level, and the community is taking notice.

The Bitcoin network’s hashrate and difficulty are at all-time highs, which typically signals strong security. However, these metrics lose meaning if control rests in too few hands.

A single coordinated action, or even a technical vulnerability or regulatory action against one of these mining pools, could destabilize the network.

That’s a systemic risk with long-term consequences. Similar fears were raised during the Pi Hackathon 2025 backlash, where centralization and delays caused significant price disruption and trust erosion.

More importantly, the shift away from decentralization could open the door to alternative protocols or Layer-1s that prioritize broader validator distribution.

For instance, Avalanche’s recent stablecoin surge demonstrates how newer networks are gaining traction by solving the very issues Bitcoin is now facing.

And in moments of institutional uncertainty, even the exit of a Story Protocol co-founder can tilt market trust, showing how sensitive the crypto ecosystem has become to leadership, structure, and decentralization risks.

The Bitcoin community must now address tough questions. Can PoW remain sustainable and decentralized at scale? Or has the mining model outgrown its founding ideals?