Base, Coinbase’s Ethereum Layer 2 network, activated its Cobalt hard fork on mainnet on September 30, following a Sepolia testnet launch on September 23. It is the network’s third upgrade of 2026 after the Azul and Beryl forks, with a fourth upgrade, Denim, expected in October.
Validity Transactions are the headline feature. They enable signed transactions that remain dormant until onchain conditions such as balance, storage, block-number, and Flashblock-index predicates are met. The Base team said a trader could submit a swap that becomes eligible only if a pool price reaches a certain USDC value before a specific block. “The API is neutral infrastructure that provides advanced traders with the added benefit of keeping their submissions private until they land,” Base explained.
The Cobalt fork also expands the B20 token standard introduced in the Beryl upgrade. Composite Policies let issuers combine allowlists and blocklists with OR or AND logic, making it possible to reuse KYC allowlists and sanctions blocklists without copying member lists. Schedule Multiplier Updates align the B20 Asset multiplier with ERC-8056 and support scheduled display changes such as stock splits. A new seizeWithMemo function allows authorized administrators to reassign a holder’s balance when seizure is enabled, recording source, destination, amount, and memo onchain.
Infrastructure changes include Dynamic upgrades, where an Ethereum smart contract stores upgrade timestamps for Base nodes; on mainnet it is initially running in metrics-only mode. Cobalt also changes TEE prover registration by verifying AWS Nitro attestations fully onchain using P-384 hints, replacing the RISC Zero and Boundless proving flow to make registration faster and remove dependence on an external proving service.
Base plans to reduce block times from two seconds to 200 milliseconds, make smart accounts native at the protocol level with gas sponsorship and transaction batching, and support a subset of EVM improvements from Ethereum’s Glamsterdam upgrade in the coming months.
