Foundry USA produced seven consecutive blocks, triggering a chain reorganization that orphaned blocks mined by AntPool and ViaBTC.
A rare two-block Bitcoin blockchain reorganization occurred on Monday, March 24, with Foundry USA – the largest Bitcoin mining pool – producing seven consecutive blocks and overwriting valid blocks mined by AntPool and ViaBTC.
In detail, the reorg started at block height 941,881, when AntPool and Foundry found valid blocks just 12 seconds apart – at 15:49:35 and 15:49:47 UTC respectively. The network temporarily split, with some nodes following one chain and others following the other.
At block 941,882, ViaBTC extended AntPool’s chain while Foundry extended its own, creating two parallel competing chains, each two blocks deep. Blocks 941,883 through 941,886 all went to Foundry, making its chain the one with the greatest cumulative proof of work. The network then recognized Foundry’s chain as the main one, “orphaning” AntPool’s and ViaBTC’s blocks.
Transactions contained in the orphaned blocks were not lost: they returned to the mempool and will be included in future blocks. An orphan block is a valid block that loses the race when two miners find blocks almost simultaneously, being permanently discarded from the chain despite being technically legitimate. A 2-block reorg does not put Bitcoin’s security at risk: the network handled the event exactly as the protocol intended, with the longest chain winning and consensus re-established within minutes.
Foundry’s size may have influenced the likelihood of this outcome. Larger mining pools are more likely to mine consecutive blocks during short-lived forks, without this necessarily implying any anomalies. When fewer pools control a larger share of hashrate, the probability that a single pool finds multiple consecutive blocks increases – and with it the likelihood of competing chains when two large pools find blocks almost simultaneously
