Bitcoin’s mining concentration problem has just appeared on the blockchain itself, triggering 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 share BTC rewards.
On the blockchain, there are many miners, and sometimes two or more find a block almost at the same time. When this happens, the network temporarily has two competing versions of the blockchain. Eventually, the network reorganizes into a single chain, based on which version is growing the fastest. This process is called blockchain reorganization, or “reorganization.”
This is what happened on Monday: Foundry and AntPool both mined blocks around the same time, causing a chain split. Foundry then produces several consecutive blocks, evolving slightly faster than its competitors, and becomes the chain followed by the network.
Result: the blockchain was reorganized according to the Foundry version, and the blocks mined by AntPool and ViaBTC were orphaned or effectively erased from the ledger. These 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 move, but suddenly one of the lines starts releasing customers faster. This causes everyone to move to the fastest line and the slowest line is abandoned.
The episode highlights the risks of mining concentration in Bitcoin and how control of network power can directly translate into outsized 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 other miners’ valid blocks.
Step by step: the split and reorganization
The event was a reorganization of the chain into 2 blocks, rare but not unprecedented, and the clearest signal on-chain yet that hashrate is becoming concentrated in fewer hands as the industry contracts.
At block height 941,881, AntPool and Foundry found valid blocks 12 seconds apart, 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 run continued to lock in 941,882, where ViaBTC extended AntPool’s chain and Foundry extended its own.
This created two competing chains, each two blocks deep, operating in parallel. Later, blocks 941,883 to 941,886 all went to Foundry, making their chain the heaviest by far.
The transactions in the orphaned blocks were not lost, however. They return to the memory pool and are 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 eliminated from the chain despite being perfectly legitimate.
A reorganization into 2 blocks does not threaten the security of Bitcoin. The network handled it exactly as expected, with the longest chain winning and consensus restored within minutes.
But when fewer pools control more hashrate, the probability of a single pool finding multiple consecutive blocks increases, and with it the probability of competing chains when two large pools find blocks almost simultaneously.
Mining difficulty just dropped 7.76% on Saturday, the second largest negative adjustment of 2026. The hash rate has fallen to around 920 EH/s from the record high of 1 zetahash reached in 2025.
Small and mid-sized miners are withdrawing because bitcoin at $70,000 is well below the estimated average production cost of $88,000. Each operator that stops concentrates the remaining hashrate into fewer pools.
