Competing blocks at height 966,500
Bitcoin experienced a small blockchain reorganization on Sept. 11 when two mining pools produced valid competing blocks at the same height. The event occurred at block height 966,500, where SpiderPool and AntPool independently built blocks on the same parent block. According to Galaxy Research, SpiderPool’s version of block 966,500 was initially treated as the tip of the Bitcoin blockchain by their node. However, AntPool also produced a valid block at the same height. The network eventually selected AntPool’s block as part of the canonical chain, leaving SpiderPool’s block stale or orphaned.
AntPool’s ultimately successful block 966,500 carried a timestamp of 11:30:30 UTC and contained 4,359 transactions. The block earned a mining reward of about 3.1411 BTC. In contrast, SpiderPool’s discarded block contained a reward of roughly 3.1389 BTC. Because the block was orphaned, this reward subsequently became unusable. The difference in rewards reflects the specific transaction data included in each version of the block, but the primary consequence for SpiderPool was the loss of the block’s place in the canonical history.
Standard proof-of-work mechanics
The reorganization process was driven by the standard proof-of-work mechanism, not a consensus bug or a successful attack on the network. Bitcoin blocks do not reach every computer on the network simultaneously, meaning different nodes may temporarily see different versions of the latest block. Galaxy Research noted that their node was initially unaware that two versions of block 966,500 existed. This situation changed when AntPool produced block 966,501 on top of its version of block 966,500.
Bitcoin nodes are programmed to follow the valid chain with the greatest accumulated proof-of-work. Upon seeing the new block, Galaxy’s node abandoned the SpiderPool version and switched to AntPool’s branch. This shift is a routine aspect of how the Bitcoin network resolves which block becomes the official record. Galaxy Research described these short-lived competing blocks as completely normal, emphasizing that the temporary divergence does not indicate instability in the underlying protocol.
Third reorg in less than a month
Galaxy Research states this was the third one-block reorganization to occur in less than a month. The previous two incidents took place at heights 962,722 and 963,853. The reorganization at height 962,722 occurred on Aug. 16, while the event at height 963,853 took place on Aug. 24. Like the recent event, these prior reorganizations involved competing blocks at the same height that resulted in one branch being extended and the other being discarded.
The frequency of these one-block reorganizations has increased in recent weeks, with three such events occurring between mid-August and early September. While the financial impact on the miners of orphaned blocks is immediate, the overall integrity of the Bitcoin blockchain remains intact. The network continues to operate under its established consensus rules, with nodes consistently selecting the longest valid chain as the source of truth.
Why It Matters
For market participants, frequent one-block reorganizations underscore the competitive dynamics among major mining pools like AntPool and SpiderPool. While these events do not compromise network security, they result in immediate financial losses for miners whose blocks are orphaned. The recurrence of such events within a short timeframe may prompt closer monitoring of mining pool behavior and network latency, though no consensus vulnerabilities have been identified.
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