The Bitcoin mining concentration issue has just appeared on the blockchain itself, prompting a small “reorganization.”
At the center of the story is Foundry USA, the largest bitcoin mining pool, representing a group of miners who combine their computing power to verify transactions, mine blocks, and split rewards in BTC.
In the blockchain, there are many miners and sometimes two or more find a block almost at the same time. When that happens, the network temporarily has two competing versions of the blockchain. Finally, the network is reorganized back into a single chain, depending on which version grows the fastest. This process is called blockchain reorganization or “reorganization.”
That’s what happened on Monday: Foundry and AntPool mined blocks around the same time, causing a chain split. Foundry then produced several consecutive blocks, moving slightly faster than its competitors, and became the chain followed by the network.
The result: the blockchain was reorganized to the Foundry version, and the blocks mined by AntPool and ViaBTC were either orphaned or effectively deleted from the ledger. Those miners earned nothing for the work they had done.
Think of it as two checkout lines opening at the same time in a busy store. At first, both lines are moving, but suddenly, one of the lines starts clearing customers faster. This leads to everyone switching to the faster line and the slower one being abandoned.
The episode highlights the risks of mining concentration in Bitcoin and how controlling the network’s power can directly translate into enormous influence and losses for rivals. When a single pool like Foundry can produce multiple blocks in a row, it can trigger a reorganization and orphan valid blocks from other miners.
Step by step: division and reorganization
The event was a rare but not unprecedented two-blockchain reorganization, and the clearest on-chain signal yet that the hashrate is concentrating in fewer hands as the industry contracts.
At block height 941,881, AntPool and Foundry found valid blocks within 12 seconds of each other, at 15:49:35 and 15:49:47 UTC respectively. Both were legitimate and the network briefly split, with some nodes following one chain and others following the other.
The race continued until locking 941,882, where ViaBTC expanded AntPool’s chain and Foundry expanded its own.
That created two competing chains, each two blocks deep, running in parallel. Later, blocks 941,883 to 941,886 all went to Foundry, making its chain the heaviest by a wide margin.
However, transactions in the orphaned blocks were not lost. They are returned to the mempool and included in future blocks. An orphan block is a valid block that loses the race when two miners find blocks at almost the same time, being permanently discarded from the chain despite being perfectly legitimate.
A 2 block reorganization does not threaten the security of Bitcoin. The network handled it exactly as designed: the longest chain won and consensus was restored within minutes.
But when fewer groups control more hashrate, the probability of a single group finding multiple consecutive blocks increases, and with it the probability of competing chains when two large groups find blocks almost simultaneously.
Mining difficulty just dropped 7.76% on Saturday, the second largest negative adjustment of 2026. Hashrate has retreated to approximately 920 EH/s from the record high of 1 zetahash reached in 2025.
Smaller and mid-sized miners are exiting because bitcoin at $70,000 is well below the estimated average production cost of $88,000. Each operator that closes concentrates the remaining hashrate into fewer pools.
