Bitcoin’s mining concentration problem came into focus on the blockchain itself when Foundry USA, the largest bitcoin mining pool, triggered a rare 2-block reorganization (reorg). The incident highlights how shrinking industry margins are concentrating hashrate into fewer, larger mining pools.
A two-block reorg occurs when two or more miners find blocks at nearly the same time, causing a temporary split in the blockchain. In this case, Foundry and AntPool both mined blocks within 12 seconds of each other, triggering a chain reorganization. The network resolved it as designed by favoring the chain with the most cumulative proof of work.
The incident underscores the risks of mining concentration in Bitcoin. When a single pool like Foundry can produce several blocks in a row, it can trigger a reorg and orphan valid blocks from other miners. This highlights the importance of having a diverse pool of miners to maintain the integrity of the network.
In recent days, mining difficulty dropped nearly 8% as hashrate retreated to around 920 EH/s. Smaller and mid-sized miners are exiting due to bitcoin’s current price being below their estimated production cost of $88,000. As a result, the remaining hashrate is concentrating into fewer pools, increasing the risk of competing chains when large pools find blocks near-simultaneously.
While a 2-block reorg does not threaten Bitcoin’s security, it increases the odds that a single pool will mine multiple consecutive blocks and create short-lived competing chains. As such, it’s essential to maintain a diverse mining pool landscape to ensure the network’s stability and resilience.
Source: https://www.coindesk.com/tech/2026/03/24/bitcoin-s-mining-concentration-just-showed-up-in-a-rare-2-block-reorg