The Bitcoin network recently experienced a two-block reorg on March 23, 2024, at block height 941,880. This event, where Foundry mined six consecutive blocks while AntPool and ViaBTC briefly extended a competing branch, resolved as designed, following the chain with the most hash rate. However, it highlighted a gap in the long-held "six confirmations" rule, a heuristic for transaction finality. Originally from Satoshi Nakamoto's 2008 whitepaper, this rule assumes an attacker controls about 10% of the network's hashpower. With Foundry holding around 32.2% of the hash rate, and Foundry, AntPool, and ViaBTC collectively accounting for approximately 60%, the modeled reversal risk after six confirmations significantly increases from 0.02% to nearly 18.9%. This concentration changes the risk model for transaction finality.

The Bitcoin network recently experienced a two-block reorg on March 23, 2024, at block height 941,880. This event, where Foundry mined six consecutive blocks while AntPool and ViaBTC briefly extended a competing branch, resolved as designed, following the chain with the most hash rate. However, it highlighted a gap in the long-held "six confirmations" rule, a heuristic for transaction finality. Originally from Satoshi Nakamoto's 2008 whitepaper, this rule assumes an attacker controls about 10% of the network's hashpower. With Foundry holding around 32.2% of the hash rate, and Foundry, AntPool, and ViaBTC collectively accounting for approximately 60%, the modeled reversal risk after six confirmations significantly increases from 0.02% to nearly 18.9%. This concentration changes the risk model for transaction finality.