Base Sets November 5 for Denim's 200ms Mainnet Blocks

Base has set November 5 for the mainnet rollout of Denim, an upgrade already live on its Sepolia testnet that replaces two-second blocks with complete blocks every 200 milliseconds.

“Denim is live on Base Sepolia with Mainnet coming November 5,” Base's verified builder account announced. Base's migration guide dates the testnet activation to October 21 at 2 p.m. ET.

For the Ethereum Layer 2, the change replaces Flashblocks—incremental updates to a pending block—with five canonical blocks a second. Each gets its own block number, hash, state root and receipts, according to Base's specification. Each still goes through the chain's confirmation and finalization process.

The November mainnet date moves the rollout beyond the October target Base previously published, as The Defiant reported in its Cobalt coverage.

Flashblocks Feeds Must Migrate

Base's migration guide tells developers to inventory every Flashblocks subscription and every request using the “pending” block tag before activation. Applications must subscribe to canonical block headers and logs instead, fetch transactions from each new block, and read canonical state rather than pending state. The old preconfirmation state has no direct equivalent after Denim.

Builders also need to audit contracts that measure time in blocks. Block numbers will advance ten times faster, so block-count-based timelocks, cooldowns, deadlines and governance voting windows will shrink to one tenth of their intended duration, Base warns. Immutable block-count settings may require a contract migration. Logic using the existing seconds-based timestamp is unaffected.

Denim adds BaseTime, a predeployed onchain contract that exposes the millisecond component of a block's timestamp while the Ethereum virtual machine's existing timestamp remains in seconds. Block, transaction and log responses also gain optional millisecond timestamp fields. Indexers must allow for those fields to be absent when authenticated historical metadata is unavailable, rather than assume every response contains them.

Tighter Token Transfer Rules

Denim also changes B20, Base's native token standard. Transfers, mints and seizures that send tokens to the token's own address will fail, preventing mistaken sends from locking funds there.

A separate executor-policy change applies authorization checks to every transfer path, including holders moving their own tokens. Issuers with restrictive executor policies must authorize holders before activation if they want holder-initiated transfers to keep working. Tokens without that policy retain the always-allow default.

The PolicyRegistry update adds a NOT flag that reverses an existing policy's authorization result without maintaining a second, mirrored list.

Native transaction batching and gas sponsorship belong to the separate Everest upgrade, whose activation dates remain unset, rather than Denim.

For node operators, Base's migration guide says the required mainnet versions of its execution and consensus clients have not yet been published.