A 12-second gap between Antpool and Foundry blocks on March 24 created a two-deep fork. Foundry won with six consecutive blocks as hashrate concentration grows.
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On March 24, 2026, Antpool mined block 941,881 at 15:49:35 UTC. Twelve seconds later, Foundry USA mined its own version of the same block. Bitcoin split into two competing chains. Foundry won by mining six consecutive blocks on its branch, forcing a reorganization that orphaned Antpool's block and one from ViaBTC.
Bitcoin mining operates without a central referee. When a miner finds a block, that block must propagate across the network before all participants agree on the latest tip. The trip takes seconds, sometimes longer. If a second miner finds a valid block before hearing about the first, both broadcast their own versions. For a brief window, two equally valid blocks exist at the same height.
Neither block violates the protocol. The only difference is timing and which nodes heard which one first. Roughly half the network mines on top of one candidate, half on the other. Bitcoin resolves the split the same way it resolves everything: whichever chain accumulates more proof-of-work becomes the accepted version. The other side's blocks get orphaned.
Orphaned blocks lose their reward and fees. Transactions confirmed only on the losing side drop back into the mempool and get picked up again. Most splits resolve after a single extra block, without anyone outside mining-infrastructure circles noticing.
A genuine two-block-deep race is rare. It requires the coin-flip odds of a tie to land twice in a row. That happened on March 24. After Antpool and Foundry each produced block 941,881, ViaBTC extended AntPool's version with block 941,882 while Foundry extended its own version. For one block the network was split down the middle. Then Foundry mined blocks 941,883 through 941,886 in succession. Its chain became "the heaviest by a wide margin," one Bitcoin developer tracking the event said.
Every node reorganized to Foundry's chain. Antpool and ViaBTC lost their blocks. The transactions were reconfirmed shortly after. Bitcoin analyst b10c, who first flagged the event publicly, called it "a rare-ish two block fork/reorg between Foundry and AntPool+ViaBTC."
The rarity is real. The event also drew attention to a less comfortable trend. Foundry stringing together six consecutive blocks is easier when a pool already commands a large share of global hashrate. Industry data shows shrinking margins have been pushing smaller miners out and concentrating hashpower into fewer, larger pools. Concentration does not make a single-block race more common. Concentration does make a well-resourced pool's odds of winning any given race and stringing together the follow-up blocks measurably better than a small miner's.
Two-block reorgs are the exception. The underlying race condition behind them is not. Data pulled from mempool.space covering the three days before the reorg (heights 941,452 to 941,887) shows 40 of 435 consecutive-block intervals landed within 60 seconds of each other. One pair was just 5 seconds apart. Every one of those close calls represents a moment when a genuine race condition existed on the network.
Almost all resolve within that same single block because the next miner overwhelmingly builds on whichever tip reached them first. Compact block relay and low-latency relay networks like FIBRE, which most large pools now use, have reduced the propagation delays that cause races. That is exactly why a race surviving two full blocks is rare enough to be newsworthy rather than routine.
The March 24 event was a reminder that Bitcoin's security model depends on propagation speed and hashrate distribution, not just total hashpower. A network where a single pool can stitch together six consecutive blocks after a split will resolve that split quickly. A network where hashpower is more evenly spread would take longer to converge, and the risk of deeper reorgs would rise. Some mining analysts said the event showed that concentration makes the network more deterministic in resolving such races, even as it reinforces centralization concerns.
Bitcoin's next difficulty adjustment is roughly two weeks away. Miners will keep racing every ten minutes.
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