Base activated its Cobalt hard fork on mainnet on September 30, the third upgrade for Coinbase's Ethereum Layer 2 this year following Azul and Beryl.
The upgrade refines the B20 token standard with scheduled multiplier updates and a simplified transfer-blocking mechanism, expanding on the framework Beryl established in June. New Union and Intersect policy types are integrated into the standard.
Cobalt introduces validity transactions—signed transactions included on Base only when specific on-chain conditions are met, such as balance, storage, block-number, and Flashblock-index predicates. This mechanism enables conditional swaps, withdrawals, and other state-dependent actions.
A new `seizeWithMemo` function allows authorized administrators to reassign a holder's balance for B20 assets and stablecoins where seizure has been explicitly enabled. Binance Wallet already supports B20 token trading, signaling early exchange integration.
Two infrastructure changes accompany the fork. Dynamic Upgrades introduces an Ethereum smart contract that stores upgrade timestamps for Base nodes, allowing them to apply changes live. The mainnet rollout is currently in metrics-only mode to gather validation data.
The second change modifies how new TEE prover signers register. AWS Nitro attestations are now verified entirely on-chain using P-384 hints, replacing the previous RISC Zero and Boundless proving processes. This speeds registration and removes dependency on external proving services. Enclave key generation, PCR0 image selection, and proof verification remain unchanged.
Base holds the largest TVL among Ethereum Layer 2s. The network's development roadmap includes the Denim upgrade, targeted for October, which aims to introduce native 200-millisecond blocks and replace Flashblocks with canonical block and RPC streams.
