The Bitcoin blockchain experienced a 1-block reorganization on Sept. 11 at block height 966500 when two major mining pools, Spiderpool and Antpool, simultaneously discovered valid blocks referencing the same preceding block.
Antpool's block joined the main chain and accumulated the most work, while Spiderpool's valid block was dropped as the network converged on Antpool's version, according to observations by Galaxy Research.
Galaxy Research detected the anomaly via its private node. The firm's node did not register Antpool's block until it was confirmed and extended by subsequent blocks.
This marks the third 1-block reorg on Bitcoin in four weeks. Previous reorgs occurred at block height 962722 on Aug. 16 and at block height 963853 on Aug. 24.
1-block reorgs are a natural part of proof-of-work consensus, where multiple miners find valid blocks at nearly the same time. Such shallow reorganizations carry minimal security risk compared to deeper chain reorganizations on other proof-of-work networks.
Monero experienced an 18-block reorg when Qubic released a previously withheld chain from block height 3,499,659. Bitcoin SV saw a 100-block reorg in summer 2021. Deeper reorganizations can cause transactions within replaced blocks to effectively disappear from the chain, introducing real security concerns.
The recent 1-block reorgs on Bitcoin, including the Antpool-Spiderpool event, do not pose the severe security risks that deeper reorganizations have presented for other chains.
