Bitcoin “six confirmations” challenged as mining pool dominance raises reorg risk

A CryptoSlate analysis says Bitcoin’s common “six confirmations” finality heuristic is being stress-tested after a rare two-block reorg on Mar. 23 at block height 941,880. The fork resolved as designed, with Foundry mining six consecutive blocks and Foundry’s chain winning over branches extended briefly by AntPool and ViaBTC. The report traces why “six confirmations” became a cultural standard, not a universal guarantee. Under Satoshi Nakamoto’s catch-up probability model, reversal risk depends on the attacker’s hashpower share. With attacker control at 10%, the model implies ~0.02% reversal risk after six confirmations; at 20% ~1.43%; at 30% ~13.2%. With Foundry’s recent pool-share snapshot around 32.2%, the implied reversal risk after six confirmations rises to about 18.9%. Key conditions cited for this “six confirmations” gap widening: (1) concentration—Foundry ~31% of global hashrate, AntPool ~18.4%, ViaBTC ~10.5% (top three ~60% of block production); (2) weakened mining economics—difficulty adjustment -7.76% on Mar. 21 and low fee contribution (~0.57% of rewards); and (3) no automatic adjustment to confirmation heuristics when pool shares shift. The article notes exchanges do not uniformly follow six confirmations (e.g., Coinbase uses two, Kraken/Gemini three) and argues that required confirmations should scale with transaction value and adversary economics rather than fixed folklore.