Base's Denim upgrade goes live, cutting block times from two seconds to 200 milliseconds and retiring Flashblocks
Base's Denim upgrade is live on mainnet. The Block reported on Thursday that the Coinbase-incubated Layer 2 now produces a full, canonical block every 200 milliseconds, down from one every two seconds, and that the protocol enforces the interval. Bankless said activation was set for 18:00 UTC, or 1 p.m. Eastern.
Denim retires Flashblocks, which Bankless said had run since July 2025. Base describes the result as simpler, more consistent and more reliable. Apps that read Flashblocks streams or the pending block tag must switch to standard block subscriptions. Smart contracts also get millisecond timestamps through a new BaseTime feature, while the usual block timestamp stays in whole seconds.
The speed-up carries a warning. Base Hub's specification says contracts that treat block numbers as time will see timelocks, cooldowns and vesting windows shrink to a tenth of their intended length, and immutable contracts cannot be fixed afterward. Bankless said Horizen, whose Layer 3 settles to Base, cannot adapt and would stop taking user transactions about 40 minutes after activation. Denim also changes the B20 token standard's compliance rules. It is Base's fourth independent upgrade after Azul, Beryl and Cobalt.
This story is reporting and analysis. It is not financial, legal or tax advice.
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