Bitcoin’s mining landscape has recently hit a notable event illustrating the growing concentration of mining power within the network. This phenomenon became evident during a recent blockchain incident resulting in a small “reorg.”
At the heart of this occurrence is Foundry USA, the largest Bitcoin mining pool, which orchestrates efforts from a variety of miners to verify transactions, mine blocks, and share the rewards in Bitcoin. In the decentralized world of Bitcoin, multiple miners can find a block nearly simultaneously, leading to a temporary split in the blockchain as different versions are established. Such scenarios, known as blockchain reorganizations or “reorgs,” generally resolve as the network reestablishes consensus around the chain that grows the fastest.
On the day in question, a race ensued as Foundry and AntPool both mined blocks within seconds of each other. Foundry quickly outpaced its competition by producing several consecutive blocks, resulting in the network’s decision to follow Foundry’s version of the chain. Consequently, the blocks mined by AntPool and another pool, ViaBTC, were orphaned—signifying those miners received no rewards for their efforts.
This event serves as a metaphorical illustration of checkout lines in a busy store: initially moving at a similar pace, one line eventually clears customers faster, attracting everyone while the slower line becomes abandoned. This highlights the dangers of mining dominance; when one pool possesses greater power, it can decisively influence the network, leading to potential losses for smaller entities.
Breaking down the sequence of the split and reorganization, a two-block chain reorganization occurred, a phenomenon rare in the Bitcoin ecosystem, but not entirely without precedent. At block height 941,881, both AntPool and Foundry discovered valid blocks within a 12-second window, sparking a brief chain split as some nodes committed to one chain and others to the other. Following this, ViaBTC managed to extend AntPool’s chain while Foundry continued to expand its own, creating a situation where both chains ran parallel for two blocks deep.
Ultimately, Foundry’s subsequent blocks from 941,883 through 941,886 cemented its chain as the dominant one. Despite the misfortune for AntPool and ViaBTC, valid transactions encapsulated in orphaned blocks were not lost; they reverted to the mempool, allowing for potential inclusion in future blocks. Such orphaned blocks, while legitimate, face elimination if found to be part of a race lost to a competing miner, underscoring the randomness of mining success.
While a two-block reorganization does not raise security concerns for Bitcoin, this incident exemplifies the intricacies of how network dynamics react when more hashrate is centered within fewer pools. Such trends elevate the likelihood of one pool discovering multiple blocks in quick succession, heightening the chances of competing chains when large pools overlap in successful mining.
This situation unfolds against a backdrop of recent shifts in mining difficulty and hashrate. A 7.76% decrease in mining difficulty was reported, marking the second-largest negative adjustment for 2026, as the hashrate receded to approximately 920 EH/s from the previous record of 1 zetahash. Smaller and mid-sized miners are increasingly exiting the market as Bitcoin’s price, currently around $70,000, remains below the estimated average production cost of $88,000. Each exiting miner amplifies the concentration of hashrate among the remaining pools, further complicating the mining ecosystem.
