Bitcoin’s mining concentration problem just surfaced on the blockchain itself, triggering a small “reorg”.
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 the rewards in BTC.
On the blockchain, there are many miners, and sometimes two or more find a block at almost the same time. When that happens, the network temporarily has two competing versions of the blockchain. Eventually, the network reorganizes back into a single chain, depending on which version grows faster. This process is called a blockchain reorganization or “reorg”.
That’s what happened on Monday: Foundry and AntPool both mined blocks at roughly the same time, causing a chain split. Foundry then produced several consecutive blocks that moved slightly faster than its competitors and became the chain the network followed.
The result: the blockchain reorganized into Foundry’s version, and the blocks mined by AntPool and ViaBTC were orphaned or effectively deleted 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 clearing customers faster. This causes everyone to switch to the faster line and the slower one to be abandoned.
The episode highlights the risks of mining concentration in Bitcoin and how controlling network power can translate directly into major influence and losses for rivals. When a single pool like Foundry can produce multiple blocks in a row, it can trigger a reorg, and orphan valid blocks from other miners.
Step by step: the division and reorganization
The event was a 2-block chain reorganization, rare but not unprecedented, and the clearest on-chain signal to date 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, respectively. 15:49:35 and 15:49:47 UTC. Both were legitimate, and the network briefly split, with some nodes following one chain and others following the other.
The run continued to block 941,882, with ViaBTC extending AntPool’s chain and Foundry extending its own.
It created two competing chains, each two blocks deep, running parallel. Later, blocks 941,883 to 941,886 all went to Foundry, making their chain the heaviest by a wide margin.
However, transactions in the orphan blocks were not lost. They return to the mempool and are included in future blocks. An orphan block is a valid block that loses the race when two miners find blocks at nearly the same time, and is permanently discarded from the chain despite being completely legitimate.
A 2-block reorg does not threaten Bitcoin’s security. The network handled it exactly as designed, with the longer chain win and consensus re-established within minutes.
However, when fewer pools control more hashrate, the likelihood of a single pool finding multiple consecutive blocks increases, and thus also the likelihood of competing chains when two large pools find blocks almost simultaneously.
Mining problems fell flat by 7.76% on Saturday, the second biggest negative adjustment in 2026. Hashrate has pulled back to around 920 EH/s from the 1 zetahash record hit in 2025.
Small and medium miners are leaving because bitcoin at $70,000 is well below the estimated $88,000 average production cost. Each operator that shuts down concentrates the remaining hashrate into fewer pools.
