The Monero (XMR) blockchain experienced its deepest chain reorganization on record over the weekend—an 18-block “reorg” that temporarily rewrote roughly 36 minutes of on-chain history and invalidated about 117–118 transactions, according to multiple monitoring sources. The event is being linked by reporters and analysts to the Qubic mining effort, which has been challenging Monero’s network security since mid-August.
Despite the unsettling technical setback, XMR’s price climbed more than 5–7% in the hours that followed, underscoring resilient investor sentiment around the privacy coin—even as the community intensifies debate over additional safeguards.
What exactly happened?
ForkLog and other outlets report that Monero’s chain was reorganized by 18 blocks on September 14, 2025, the largest such rollback in the network’s 12-year history. Cointelegraph notes around 117 transactions were reversed; Decrypt/Yahoo Finance puts the figure at 118, with the depth equating to roughly 36 minutes of block history.
Independent node operators flagged the event on X (formerly Twitter), and subsequent coverage tied it to the same actors involved in last month’s Monero turbulence. ForkLog’s English edition framed it as the biggest reorg in 12 years, citing community observations.
Why Qubic is at the center of the story
Coverage by Cointelegraph and others links the reorg to Qubic, a mining effort associated with IOTA co-founder Sergey Ivancheglo, which claimed or amassed majority-level hash power against Monero in August. That earlier incident prompted Kraken to pause XMR deposits as a precaution, before later re-enabling them with stricter confirmation requirements. This weekend’s event appears to be the most dramatic consequence to date of that hash-power concentration.
Why the reorg depth matters
Monero historically relied on a 10-block lock as a practical safety buffer; Sunday’s 18-block reversal exceeded that threshold, according to Cointelegraph’s account citing community researcher commentary. Practically, this means merchants and exchanges may now extend the number of confirmations they require for high-value XMR deposits and payments until confidence is restored.
Some developers and community members have also floated temporary defenses—such as DNS or rolling checkpoints—to limit how far a chain can be reorganized in real time. Logs from the Monero Research Lab channel show prior discussion of checkpointing depth and design trade-offs in recent days, reflecting an active search for mitigations. (Critics warn such measures can increase centralization and must be weighed carefully.)
Market reaction: resilience, with caveats
In a counterintuitive twist, XMR rallied after news of the reorg became public, with several outlets citing 5–7% intraday gains. As of Monday afternoon (Bangkok time), XMR traded near $309, according to live market data. The bounce suggests that—at least for now—traders perceive the incident as containable, or that buyers faded fear-driven headlines. Still, the security optics are hard to ignore: a privacy coin’s value proposition hinges on credible, censorship-resistant settlement.
How we got here: a brief timeline
- Aug. 12–18, 2025: Qubic publicly claims majority hash power over Monero; Kraken temporarily pauses XMR deposits and later re-enables them with heightened confirmations. The episode focuses industry attention on Monero’s mining distribution and reorg defenses.
- Mid-Aug to early Sept.: Deeper-than-usual reorgs (e.g., six blocks) are discussed by analysts and on Monero forums; checkpointing proposals and other mitigations are debated in public channels.
- Sept. 14, 2025: The 18-block reorg occurs, reversing ~117–118 transactions—the largest rollback on Monero to date. Coverage spreads across crypto media.
What is a “reorg” and why it’s serious
A blockchain reorganization replaces a recent stretch of blocks with a longer, competing chain—effectively rewriting that segment of history. Reorgs happen naturally at shallow depths on many Proof-of-Work networks. But deep reorgsraise red flags because they invalidate confirmed transactions, delay finality, and open the door to double-spend attempts by an attacker with enough hash power. Monero’s 18-block incident stands out on all three counts.
What the community might do next
Short-term operational changes (like waiting more confirmations for deposits) are likely while developers evaluate structural fixes. The checkpointing debate—using periodic, rolling checkpoints to finalize blocks beyond a certain depth—has resurfaced. Proponents argue it stops extreme reorgs; skeptics worry about centralization and reliance on off-chain signaling. Developer discussions captured in public logs indicate draft proposals are being explored, though any change will need broad review and testing.
Broader implications for privacy coins
For Monero—and privacy-focused cryptocurrencies more broadly—the incident underlines a classic trade-off: robust, decentralized mining is a security cornerstone. Where hash power clusters (even temporarily), networks become vulnerable to reorgs and censorship. Sunday’s event will likely reignite conversations about miner incentives, pool diversity, and whether protocol-level tweaks can harden finality without eroding Monero’s ethos.
Key facts at a glance
- Depth: 18 blocks (≈36 minutes of history).
- Impact: ~117–118 transactions reversed and re-mined.
- Attribution (per media): Linked to Qubic amid ongoing hash-power pressure.
- Price move: XMR +5–7% intraday despite the scare.
- Next steps: More confirmations recommended; debate over checkpointing and related mitigations ongoing.