Base, the Coinbase-backed Ethereum Layer 2 network, activated its Cobalt hard fork on mainnet on September 30 at 18:00 UTC, following a week-long trial on the Sepolia test network. The upgrade shipped without significant disruption, according to initial reports from the hours after activation.

Cobalt is the third major hard fork in Base's 2026 roadmap and introduces a set of infrastructure-level changes aimed at transaction flexibility, upgrade automation and signer registration. Node operators were required to update to Base v1.4.2 or newer before activation, while Binance halted transfers on the Base network during the upgrade window as a precaution.

What Cobalt changes

The upgrade refines the B20 native token standard, a precompile originally introduced during the Beryl upgrade. The changes affect how the standard operates under the hood, with the practical effect for users being improved reliability and consistency when interacting with tokens built on the standard.

The most consequential addition is the introduction of validity and conditional transactions. These allow a transaction to execute only if specific on-chain conditions are verified at the time of inclusion. If the conditions are not met, the transaction does not execute.

Cobalt also establishes a framework for dynamic on-chain upgrade scheduling. Coordinating hard forks previously required manual intervention and, in some cases, full restarts of client systems. The new framework allows future upgrades to be scheduled and executed with less operational friction, reducing downtime and coordination overhead for node operators.

Finally, the upgrade accelerates registration for Trusted Execution Environment (TEE) signers by moving verification fully on-chain. Removing the dependency on off-chain verification steps tightens the security model while shortening the registration process.

Compatibility and rollout

For developers and protocols deployed on Base, the Cobalt changes are largely backward-compatible. The node software update was mandatory, but application-level code should not require significant changes. The new transaction types are additive, meaning existing transaction formats continue to function as before.

The activation followed a week of testing on Sepolia, and no notable issues surfaced in the hours after Cobalt went live on mainnet.

Aggressive cadence

Base has maintained an aggressive upgrade cadence in 2026. Azul activated on June 25, Beryl followed, and Cobalt landed at the end of September. Denim, the fourth upgrade in the series, is targeted for October 2026. Four hard forks in roughly four months reflect a deliberate strategy of shipping improvements incrementally rather than bundling them into a single high-risk upgrade.

With Denim scheduled for next month, node operators face another mandatory software cycle in short order, and the new on-chain scheduling framework introduced in Cobalt will face its first practical test in coordinating that rollout.