Base, the Ethereum Layer 2 built by Coinbase, activated its Denim upgrade at 18:00 UTC on Thursday, according to the network’s status page. The first 200‑millisecond block (number 53,556,127) was recorded one second after activation, marking a ten‑fold acceleration from the previous two‑second block cadence. Base confirmed the upgrade as “officially live on mainnet” in a post on X shortly after the rollout.

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How Denim changes block timing

Denim rewrites the block interval from two seconds to 200 ms, turning every partial result that Flashblocks previously emitted into a full block with its own hash, safety, and finality stages. The change shrinks any duration measured in block counts to one‑tenth of its original length, affecting governance votes, vesting schedules, cooldowns, and other time‑locked mechanisms that reference block numbers, according to the Denim specification. Contracts that read `block.timestamp` remain unaffected because timestamps still advance in whole seconds, but a new BaseTime contract now exposes millisecond‑precision timestamps, and RPC responses can include optional millisecond fields.

Migration and immediate impact

Applications that relied on Flashblocks must migrate to the canonical block and RPC streams; the migration guide maps old Flashblocks subscriptions to standard ones and notes that the `pending` block tag has no direct equivalent after Denim. Node operators are required to run base/base v1.5.1 or later, with version v1.5.3 later addressing a separate state‑root bug. Fourteen minutes after activation Base reported “periodic transaction inclusion delays, causing a higher than expected rate of empty blocks.” Unchained’s data showed 146 of the first 300 blocks were empty, though later hourly samples showed no empties.

Effects on dependent chains

Horizen, a Layer 3 built on the OP Stack and settling to Base, announced that it could not continue operating after Denim’s launch. The Horizen DAO gave users until 13:00 UTC on Nov. 4 to move assets, after which remaining balances will be returned to holders. The incident underscores the upgrade’s broader impact on ecosystems that depend on Base’s block cadence.

What to watch next

The next scheduled upgrade for Base, code‑named Everest, has no announced date, but observers will monitor how developers adjust time‑sensitive contracts and whether other Layer 3s can adapt to the new block speed. Additionally, the frequency of empty blocks and any lingering transaction‑inclusion delays will be key metrics as the network stabilises.