Base's Denim upgrade goes live with native 200ms blocks, retiring Flashblocks

Summary

Base said Thursday its fourth mainnet upgrade, Denim, is live, replacing Flashblocks with native canonical blocks every 200 milliseconds—five complete blocks per second—according to the project's blog and The Block.

Before Denim, Base produced one canonical block every two seconds while Flashblocks streamed pending-state previews; Base said each 200ms block is now a real canonical block with protocol-enforced timing, and Flashblocks streams plus pending-state semantics are retired.

Denim also adds BaseTime, giving contracts and RPC clients millisecond-resolution timestamps while leaving Ethereum-compatible block.timestamp in whole seconds, Base said; The Block likewise reported new millisecond fields on blocks, transactions and logs.

For B20 tokens, Denim adds a NOT operator for reusable compliance policies, extends transfer-executor checks to direct transfers, and rejects transfers, mints or seizures whose recipient is the token contract's own address, Base said.

The Block noted Denim follows Azul, Beryl and Cobalt—Base's first three independent upgrades since its 2023 launch—and that apps that relied on Flashblocks must migrate to standard canonical subscriptions such as eth_subscribe("newHeads").

Key facts

• Base: "Denim brings native 200ms blocks to Base that replaces flashblocks: five complete canonical blocks every second." (Base)
• Base warned that block.number now advances ten times faster in wall-clock time, so contracts that treat block counts as durations need review; block.timestamp is unchanged. (Base)
• Inclusion in a 200ms block does not by itself make a transaction final; safety and finality still depend on Ethereum batch posting and finalization, Base said. (Base)
• The Block said Base described Denim as making block production "simpler, more consistent, and more reliable." (The Block)