Ethereum Layer 2 scaling solution Starknet experienced a significant mainnet outage on September 2, 2025, halting transaction processing for approximately four hours. The disruption began at 2:23 am UTC and lasted until 4:36 am UTC, during which block production stalled and transactions remained unprocessed.
Developers identified the issue as stemming from the network's sequencer failing to recognize Cairo0 code, a critical component for transaction ordering. To resolve the outage, the Starknet team executed a blockchain reorganization (reorg) starting from block number 1,960,612, effectively rolling back one hour of network activity. This required users to resubmit transactions submitted during the affected period.
This marks the second major outage on Starknet's mainnet within two months, following a 13-minute disruption on July 18, 2025. The recent incident has raised concerns about network reliability, particularly as Starknet ranks as Ethereum's seventh-largest L2 with $548 million in total value locked (TVL).
The outage occurred amidst Starknet's ongoing Grinta upgrade, which aims to enhance decentralization through changes to the sequencer, fee market, and mempool systems. The upgrade has introduced technical challenges including slow block creation and gateway inactivity. Despite these setbacks, Starknet continues to advance its decentralization efforts, including the community-approved SNIP-31 proposal that will integrate Bitcoin staking with a 25% weighting in its consensus mechanism.
The network has since resumed normal operations, with most RPC providers back online and remaining nodes undergoing upgrades. The Starknet team has committed to publishing a full retrospective analysis including root cause identification and long-term prevention measures.