Base, Coinbase’s Ethereum Layer 2, is set to activate its Cobalt hard fork on mainnet on September 30, according to Base’s upgrade documentation . The network upgrade, already live on the Base Sepolia testnet since September 23, improves the B20 token standard, adds conditional validity transactions, lays groundwork for onchain-scheduled node upgrades, and changes how trusted-execution-environment (TEE) provers register. It is the network’s third upgrade of 2026, following the Azul and Beryl forks, with a fourth, Denim, targeting October.
What Cobalt adds to the network
Cobalt expands the B20 token standard with scheduled multiplier updates, a simplified transfer-blocking mechanism, and new Union and Intersect policy types. The Beryl fork made Base a first-class issuance platform for B20 tokens, and Cobalt widens that standard rather than replacing it. The upgrade also introduces validity transactions: signed transactions that Base includes only when onchain conditions such as balance, storage, block-number, and Flashblock-index predicates match. The mechanism enables conditional swaps, withdrawals, and other state-dependent actions.
Dynamic upgrades and a new prover registration flow
The fork ships two infrastructure changes. Dynamic upgrades introduces an Ethereum smart contract that stores upgrade timestamps for Base nodes, so they can query the contract and apply changes live; on mainnet it is rolled out in metrics-only mode while Base collects data to validate that upgrades work smoothly. Cobalt also changes how new TEE prover signers register: AWS Nitro attestations are verified fully onchain using P-384 hints, replacing the RISC Zero and Boundless proving flow, so registration is faster and no longer depends on an external proving service. Enclave key generation, PCR0 image selection, and proof verification stay unchanged.
Cobalt builds on Base’s B20 rollout
Base, built on the OP Stack, has grown into one of the most-used Ethereum Layer 2 networks, and Cobalt refines the B20 issuance platform introduced in the Beryl upgrade. The standard has already drawn exchange support, including Binance Wallet’s B20 token trading , while Base’s position as the largest Ethereum Layer 2 by total value locked makes each protocol upgrade a closely watched event for developers and traders. The fork continues a busy 2026 schedule: Azul strengthened security and decentralization in May, and Beryl added B20 tokens and reduced withdrawal delays in June. The next upgrade, Denim, is targeting October with native 200-millisecond blocks that replace Flashblocks with canonical block and RPC streams.
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