Base's Cobalt upgrade adds validity transactions and new B20 token policies
Serguey Asael Shinder2 min readBase, the Ethereum layer 2 network incubated by Coinbase, activated its Cobalt hardfork on mainnet on 30 September. Node operators had to run version 1.4.2 of the Base node software by 18:00 UTC that day, according to the release notes, which point to Base's documentation for what changed. The upgrade touches four areas.
Validity transactions. Cobalt introduces signed transactions that Base includes only if onchain conditions match at the time of inclusion: predicates on contract storage, on the block number, or on the index of the Flashblock, Base's sub-block unit. The documentation names conditional swaps and withdrawals among the uses. For users this means a transaction can state the state it expects and simply not land if that state has changed, rather than executing against something different.
B20 token standard. Base's B20 standard for tokens gets scheduled updates to its multiplier, a simplified way of blocking transfers, and two new policy types, Union and Intersect, for combining rules. These are the controls issuers of regulated or tokenised assets use to decide who can hold and move a token.
Dynamic upgrades. A new Ethereum contract stores upgrade timestamps that Base nodes can query to apply changes live. On mainnet it runs in metrics-only mode for now, while data is collected to check that the mechanism works.
Signer registration. New Trusted Execution Environment signers are now registered by verifying AWS Nitro attestations fully onchain, replacing a flow that relied on RISC Zero and Boundless to produce proofs offchain. Base says registration is faster and no longer depends on an external proving service, while key generation and proof verification are unchanged.
Why it matters
Validity transactions move a check that usually lives in application code - "only if the price or balance is still what I saw" - into the protocol. The B20 changes point the other way: more control for token issuers, which is what tokenised-asset issuers ask for and what some users will watch closely.