Base has activated its Denim upgrade on mainnet, replacing a two-second canonical block cadence with five complete blocks per second. The Coinbase-incubated Ethereum layer-2 network said the upgrade switched on at 18:00 UTC on November 5. Fourteen minutes later, its status page confirmed successful activation while also reporting periodic transaction inclusion delays and a higher-than-expected rate of empty blocks.

Native blocks replace Flashblocks

Denim changes the network's rapid-feedback system rather than simply speeding up the same block structure. Base's technical documentation says each 200-millisecond interval now produces a complete canonical block with its own hash, state root, receipts and fork-choice lifecycle. That replaces Flashblocks, which previously streamed partial preconfirmation updates while a standard two-second block was being assembled. Applications still consuming Flashblocks streams or relying on the pending block tag need to move to canonical block and RPC feeds.

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Millisecond timing reaches contracts and APIs

The upgrade also introduces BaseTime, a predeploy that supplies the sub-second component of block time. Ethereum Virtual Machine block timestamps remain measured in whole seconds, but contracts can use BaseTime for millisecond precision. RPC responses for blocks, headers, transactions, logs and receipts can now include optional millisecond fields. Base says those fields are derived from authenticated metadata and may be absent for historical data when the underlying block body or metadata is unavailable.

Block-count timers need review

Faster blocks can alter application behavior when contracts treat a fixed number of blocks as a proxy for elapsed time. Independent coverage by Bankless highlighted timelocks, vesting schedules and governance windows as areas that can run ten times faster if developers leave block-count parameters unchanged. Base advises developers to use timestamp comparisons where possible and to assess immutable contracts that cannot be retuned. The change is operationally significant even though users were already receiving fast feedback from Flashblocks.

B20 transfer rules also change

Denim includes several changes to Base's B20 token standard and PolicyRegistry. Transfers, mints and seizures to a token's own address now revert, the transfer-executor policy applies across transfer paths, and policies can be inverted with a NOT flag. These adjustments are designed to make policy enforcement more consistent, while the BaseTime and RPC changes give applications a common way to work with the faster block cadence.

What users should expect

For ordinary transfers and application interactions, Denim's most visible effect should be a faster stream of confirmed Base blocks. It does not make those blocks equivalent to final settlement on Ethereum: a transaction can appear in a Base block before its batch is posted to Ethereum and before Ethereum finalizes that batch. Wallets, exchanges and explorers therefore still need to communicate the difference between inclusion, safety and finality. The current inclusion delays also mean the theoretical 200-millisecond cadence does not guarantee every transaction will enter the next available block.

Activation is live, but monitoring continues

The activation did not conclude without operational questions. Base's status page placed the upgrade in a verifying state because some transactions were taking longer to be included and empty blocks were appearing more often than expected. At the time of verification, the public dashboard showed block production, deposits, withdrawals and batch submission as operational, while the transaction pool was marked as degraded. The network had not posted a resolution for the Denim-related delay. Developers and users should therefore distinguish successful protocol activation from full stabilization of transaction flow.

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