Bitcoin Gold rejected a 1,300-block attack chain on July 10, 2020

On July 10, 2020, Bitcoin Gold’s accepted network rejected an alternate blockchain containing more than 1,300 blocks, according to the project’s developers and repository records. The episode mattered because it showed both the vulnerability of a smaller proof-of-work network to deep chain reorganizations and the power that emergency checkpoints gave software maintainers and infrastructure operators over which history nodes would accept.

What the network rejected

Bitcoin Gold’s team said the unknown miner began building the alternate history on July 1, 2020, and released it to the network on July 10. The chain extended for more than 1,300 blocks. In ordinary proof-of-work consensus, nodes generally prefer the valid chain with the most accumulated work. A sufficiently powerful miner can exploit that rule by privately building a rival history and releasing it later, potentially reversing payments made on the public chain.

The project had prepared for that possibility. Bitcoin Gold Core version 0.17.2, released on July 2 at 06:48 according to GitHub’s release record, added a checkpoint at block height 640,650. The checkpoint fixed one specific block as part of the history recognized by upgraded software. Because the alternate chain diverged before that point, nodes running the update rejected it even if the rival chain presented more accumulated work.

The code record verifies that version 0.17.2 existed and that the checkpoint was embedded in Bitcoin Gold’s chain parameters. A later repository note, edited on July 27, records that the more-than-1,300-block chain was released on July 10 and rejected. CoinDesk’s report published at 10:21 p.m. Eastern on July 10 also attributed the sequence to Bitcoin Gold’s developers.

Security succeeded, decentralization became the question

The immediate operational result was favorable: the developers said the accepted chain continued and the rival history did not replace it. No source reviewed for this reconstruction establishes a completed double-spend, a loss amount, or the attacker’s identity. Calling the episode an attempted 51% attack therefore describes the developers’ assessment of the long private chain, not an independently proven motive.

The defense nevertheless exposed a governance tradeoff. A checkpoint can protect exchanges, miners and users from a deep reorganization, but it suspends the normal most-work rule at a chosen height. Its effectiveness depends on operators adopting the software and agreeing on the designated history. Bitcoin Gold’s developers said major mining pools and exchanges had received or adopted the update; the surviving records reviewed here do not provide a complete operator-by-operator adoption list.

That distinction was institutionally important on July 10, 2020. Exchanges accepting deposits from proof-of-work networks had to manage confirmation depth and reorganization risk, while node operators had to decide whether an emergency release represented a necessary security boundary or excessive reliance on maintainers. The checkpoint stopped the reported chain from becoming canonical for upgraded nodes, but it did not remove the underlying economics that allowed an unknown miner to construct such a long alternative.

Market context and limits

CoinDesk reported that BTG traded between $9 and $10 on Bitfinex from July 7 through its July 10 publication and said the attempted takeover had not visibly moved that venue’s price. That is a single-exchange BTG price window, not a global benchmark or proof that the event had no market effect. This reconstruction makes no return calculation and does not infer market-wide volume, liquidity or losses from that observation.

Later-record context

The July 27 repository note supplies the cleanest surviving technical summary, but it postdates the event and is used only to clarify the mechanism. The event-day framing remains limited to what was reported on July 10: developers said an emergency checkpoint caused upgraded Bitcoin Gold nodes to reject a long rival chain, while the attacker’s purpose and any intended transactions remained unverified.