[Urgent] Base - Sepolia - Upgrade to v1.4.0

Scheduled for Sep 21, 00:00 UTC - Sep 22, 00:00 UTC

Scheduled

We are upgrading our Base Sepolia infrastructure to v1.4.0 ahead of the Cobalt hardfork, scheduled for September 23, 2026 at 18:00 UTC.

During the maintenance window, brief interruptions to RPC availability may occur.

RPC Changes:
- Cobalt introduces validity transactions — signed transactions that only execute onchain when specified conditions (balance, storage, block number, or Flashblock index) are met, enabling conditional swaps, withdrawals, and other state-dependent actions via standard transaction submission.
- Cobalt also brings improvements to the B20 token standard, including the ability to pay transaction fees in B20 tokens, scheduled multiplier updates, and new Union/Intersect policies.

https://github.com/base/base/releases/tag/v1.4.0

Posted Sep 17, 2026 - 17:42 UTC

This scheduled maintenance affects: Base (Sepolia - JSON-RPC API).