Base replaces Flashblocks previews with native 200-millisecond blocks

Base says its Denim upgrade is live on mainnet, producing five complete blocks per second instead of one every two seconds. The 5 November release replaces Flashblocks previews, while Ethereum settlement still determines stronger finality.

Previously, Flashblocks supplied incremental previews while a full Base block was assembled. Denim makes the faster updates canonical blocks that ordinary applications can read through standard interfaces. For users, the intended benefit is quicker inclusion and more consistent application state, rather than a separate preview that must later be reconciled.

Base explicitly cautions that inclusion in a 200-millisecond block is not final settlement. Batches still need to be posted to Ethereum and finalised there. A faster receipt should therefore not be presented as an instant, irreversible cross-chain guarantee.

The upgrade also adds millisecond time information and changes transfer controls for B20 assets. One concrete warning for application operators: block numbers now advance ten times faster, so timers expressed as a count of blocks need review. A cooldown that was designed around the old cadence can become much shorter even if its code has not changed.