Arbitrum Sepolia stalls for hours as Nitro issue halts block production

Arbitrum’s Sepolia testnet has experienced a partial outage, with block production halted for several hours due to a suspected issue in its core Nitro infrastructure.

In an update shared by the Arbitrum developers, the team said block production was temporarily paused after identifying a potential block divergence linked to Nitro, the network’s execution engine. 

The team is currently working on an infrastructure update, with a new Nitro release expected to restore normal operations.

Testnet activity frozen as blocks stop advancing

Data from the Arbitrum Sepolia explorer shows that no new transactions have been processed for roughly 3–4 hours. This confirms that the network is not merely delayed but fully stalled.

The latest recorded batches and transactions are timestamped several hours ago, and the explorer shows it is still “scanning new transactions” with no new activity. This suggests the chain has effectively stopped advancing during the outage.

Nitro issue causes block divergence

According to the team, the root cause appears to be related to Nitro, Arbitrum’s core scaling and execution system.

Block divergence occurs when nodes disagree on the state of the chain, preventing consensus and halting block production. In such cases, networks are typically paused to avoid inconsistencies or further errors while a fix is prepared.

Arbitrum said no action is required from infrastructure providers at this stage. Still, node operators will need to upgrade once a patched Nitro version is released.

Developers advised to pause testing

The outage primarily affects developers using the Sepolia testnet for contract deployment and testing.

Arbitrum has advised developers to:

• Pause time-sensitive testing
• Consider alternative environments until recovery

Infrastructure providers, including validators and RPC operators, have also been warned to expect a stalled chain head until block production resumes.

No funds at risk as mainnet remains unaffected.

The team emphasized that no user funds are at risk, as the issue is limited to the Sepolia testnet environment.

While testnet outages do not impact live user assets, they can disrupt development workflows and highlight underlying infrastructure risks within core systems.

Recovery underway with update expected

Arbitrum said it is actively investigating the issue and will release a new Nitro version to resolve the divergence and restart block production.

Further updates are expected as the team progresses toward restoring normal network operations.

Final Summary

• Arbitrum’s Sepolia testnet has been frozen for hours, with no new transactions processed due to a Nitro-related block divergence.
• While no funds are at risk, the outage underscores how core infrastructure issues can halt blockchain activity entirely, even in controlled environments