Bitcoin’s mining concentration problem has just manifested itself on the blockchain itself, triggering a small-scale “reorganization.”
At the center of the story is Foundry USA, the largest Bitcoin mining pool and representing a group of miners who combine their computing power to validate transactions, mine blocks and split BTC rewards.
On a blockchain, there are many miners, and sometimes two or more miners 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 back into a single chain, depending on which version grows faster. This process is called a blockchain reorganization or “reorganization”.
This is what happened on Monday: Foundry and AntPool mined blocks at almost the same time, causing the chain to split. Foundry then produced several consecutive blocks that moved slightly faster than its competitors and became the chain that the network followed.
Result: The blockchain was reorganized into Foundry’s version, with blocks mined by AntPool and ViaBTC being orphaned or effectively removed from the ledger. These miners gained nothing from their work.
Think of it like two checkout lines open at the same time in a busy store. At first, both lines were moving, but suddenly one of the lines started clearing customers faster. This results in everyone switching to the faster team and slower teams being abandoned.
The incident highlights the risks of Bitcoin mining centralization and how control over the power of the network translates directly into huge impacts and losses for competitors. When a single mining 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: splitting and restructuring
This event is a 2-blockchain reorganization, rare but not unprecedented, and the clearest on-chain signal to date that computing power is concentrating into fewer hands as the industry shrinks.
At block height 941,881, AntPool and Foundry discovered valid blocks within 12 seconds at 15:49:35 and 15:49:47 UTC respectively. Both are legal and the network briefly splits with some nodes following one chain and other nodes following the other.
The competition continued with the number of blocks reaching 941,882, with ViaBTC extending AntPool’s chain and Foundry extending its own chain.
This creates two competing chains, each two blocks deep, running in parallel. Later, blocks 941,883 to 941,886 all entered Foundry, making their chain the heaviest chain.
However, transactions in orphan blocks are not lost. They are returned to the memory pool and included in future chunks. An orphan block is a valid block that loses the race when two miners find the block at almost the same time and, although perfectly legal, is permanently discarded from the chain.
The reorganization of 2 blocks does not threaten the security of Bitcoin. The network behaves exactly as designed, with the longer chain winning and consensus re-established within minutes.
However, when fewer pools control more computing power, the probability of a single pool finding multiple consecutive blocks increases, and when two large pools find blocks almost simultaneously, the probability of competing chains increases.
On Saturday, mining difficulty dropped by 7.76%, the second largest negative adjustment in 2026. The computing power has dropped back to about 920 EH/s from the 1 Zetahash record set in 2025.
Small and medium-sized miners are exiting because Bitcoin at $70,000 is well below the estimated average production cost of $88,000. Each operator that shuts down will concentrate the remaining computing power into fewer pools.