Monero Faces Blockchain Reorg After Qubic Gains 51% Hashrate

Qubic announced on August 12 that it reached 51% of Monero's mining power and “successfully reorganized the blockchain.” The AI-focused project, led by IOTA co-founder Sergey Ivancheglo, described the effort as a demonstration of its “useful proof-of-work” model.

The announcement coincided with a six-block reorganization on Monero's network. Community monitoring dashboards recorded dozens of orphaned blocks during the same period. Qubic spent August directing miners to its pool to achieve majority hashrate control.

Public updates from Qubic show the campaign began with a “takeover test” window starting August 2, followed by multiple “marathons” of redirected mining power. Earlier reports indicated the project reached peaks near half of Monero's total hashrate before this week's push to cross the majority threshold.

Developers and researchers expressed concerns about sustained majority control enabling deeper reorganizations, transaction censorship, or double-spending attacks. However, debate continues over whether the observed activity constitutes a full 51% attack.

Luke Parker, lead developer of Serai DEX, questioned the severity of the incident. “A 6 re-org does not mean a ‘51% attack' was successful,” Parker stated. The comment reflects ongoing disagreement among technical observers about the demonstration's impact.

Qubic framed the effort as an experiment rather than an attack. The project's blog post emphasized the demonstration aspect: “Qubic reached 51% of Monero's hashrate dominance, successfully reorganizing the blockchain.”

Monero uses the RandomX algorithm designed to favor CPU mining over specialized hardware. The approach aims to prevent mining concentration, but coordinated efforts directing existing miners to single pools can still create temporary dominance scenarios.

The situation remained active as of August 13, with claims and responses continuing among project teams and network observers. Independent verification of sustained majority control remains under discussion among developers and researchers monitoring the network's hashrate distribution.

The incident highlights ongoing vulnerabilities in proof-of-work networks where coordinated mining efforts can achieve temporary majority control, even on privacy-focused chains designed to resist centralization.