TLDR
- Monero experienced its largest-ever chain reorganization involving 18 blocks.
- The reorg erased 36 minutes of transaction history and invalidated over 100 transactions.
- The incident began at block height 3,499,659 and lasted for almost 40 minutes.
- The Monero Research Lab confirmed the event exceeded the standard 10-block confirmation threshold.
- Developers advised implementing DNS checkpoints to improve network stability.
A recent Monero network event caused an 18-block reorganization that erased about 36 minutes of transaction data. The reorg invalidated over 100 transactions, forcing developers to reassess network safeguards. Community members labeled this the “largest reorg in Monero’s history,” raising new concerns about transaction finality.
Monero Reorg Overrides 18 Blocks of Data
Monero experienced an 18-block reorg that began at block height 3,499,659 and lasted nearly 40 minutes. During the incident, nodes saw an alternate chain that temporarily held around 117 to 118 transactions. These transactions became invalid when the network converged on the longer and more difficult chain.
The Monero Research Lab explained that the 10-block confirmation standard did not protect all affected users. The organization added that the chain rollback exceeded the default confirmation threshold, leaving some users exposed. They advised developers to consider a DNS checkpoint update to strengthen the network.
This reorg has led to warnings across the Monero ecosystem, especially regarding payment finality. Reorganizations are not uncommon in proof-of-work systems, but few reach this scale. In response, some recommended increasing confirmation requirements for large payments in Monero.
XMR Remains Resilient Despite Network Uncertainty
Despite the network disruption, Monero’s native token XMR rose 3.70%, briefly gaining over 6% following the event. Market data showed that while Monero reacted with price gains, QUBIC remained flat during the same window. This price reaction surprised some traders, considering the scale of the technical issue.
"Analyst" was used in https://t.co/eGAuGCIVWs because @xenumonero pulled all that out of his ass.#Monero #Qubic pic.twitter.com/0dXVu5of3J
— Come-from-Beyond (@c___f___b) September 14, 2025
Speculators suggested the incident might involve Qubic, a mining protocol previously linked to high Monero hashrate. The unknown mining pool behind the reorg reignited concerns about Qubic’s influence on the Monero network. Qubic had earlier stopped reporting its hashrate, which fueled further speculation.
Xenu, a Monero community podcaster, claimed Qubic used “selfish mining” tactics in the reorg. He noted, “This is the largest reorg in Monero’s history,” pointing to isolation mining behavior. However, Qubic founder Sergey Ivancheglo denied those claims and publicly dismissed the accusations.
Community Raises Reorg and Double-Spend Risks
Security experts warned that ignoring reorg risks may allow double spending even without a majority of the network’s hash power. Yu Xian from SlowMist said the threat remains serious if miners isolate blocks to rewrite transaction history. He urged developers and users to remain alert during high-volume Monero activity.
Recently, an 18-block re-org occurred on Monero's mainnet. You can check this by inputting alt_chain_info into your monerod console if your node was operating during the re-org:
18 blocks long, from height 3499659 (437 deep), diff 510191663980291508:…
— Monero Research Lab (Unofficial) (@MoneroResearchL) September 14, 2025
The incident revived discussions about mining power concentration within the Monero ecosystem. Earlier in the year, Qubic was accused of controlling over 50% of Monero’s hashrate. Although unverified, these concerns have resurfaced with the latest reorg.
Monero developers continue to evaluate potential responses, including temporary DNS checkpoints. This could harden the network against similar reorganizations and help protect transaction stability.
