denim

Base, the Coinbase-backed network, has tightened its block-production cadence by a notch on testnet first.
On October 21, Jesse Pollak posted a short message: “200ms blocks live on testnet, mainnet soon.” According to the official docs, this is the Denim upgrade: Base Sepolia is scheduled to switch to native 200-millisecond block production at 18:00 UTC—going from one block every 2 seconds to five full canonical blocks per second. The old Flashblocks preconfirmation stream is being retired, and apps will need to migrate to subscriptions such as canonical newHeads.
The key caveat: each 200ms block has its own hash, state root, and receipt lifecycle. EVM's block.timestamp still advances in seconds, with milliseconds supplied by BaseTime metadata. But block.number advances about 10 times faster—once mainnet catches up, any contract that uses a number of blocks as a cooldown will see that period shrink to one-tenth its original length. Mainnet is targeted for November, but the docs warn that months without a firm date are only tentative plans and may change.