Base’s Denim mainnet upgrade replaces Flashblocks with full canonical blocks every 200 milliseconds, or five blocks per second, according to a project statement shared with The Block on November 5, 2026.
For developers, the documented changes concern block subscriptions, timestamp precision and B20 token controls. Denim is the Coinbase-incubated Layer 2’s fourth independent network upgrade.
Flashblocks applications must change subscriptions
Base said applications that relied on Flashblocks must migrate to standard canonical block subscriptions. Denim retires Flashblocks and changes the behavior of the pending block tag.
Under the upgrade, each block follows its parent exactly 200 milliseconds later. The protocol enforces that interval rather than relying on the sequencer’s clock. Base described the change as making block production “simpler, more consistent, and more reliable.”
The supplied announcement does not include subscription code or detail the revised pending tag behavior, so it is not a complete migration guide.
BaseTime adds millisecond precision without changing block.timestamp
Denim introduces BaseTime, giving smart contracts access to Unix timestamps in milliseconds. The existing Ethereum-compatible block.timestamp remains at whole-second resolution.
New RPC fields also provide millisecond timestamps for:
- Blocks
- Transactions
- Logs
The distinction matters when reviewing an integration: BaseTime adds finer-grained time access, but the upgrade does not make block.timestamp millisecond-resolution.
B20 transfer and compliance controls expand
For tokens using Base’s B20 standard, Denim introduces reusable compliance policies through a NOT operator and extends transfer-executor restrictions to direct transfers.
Base also said the upgrade blocks transfers, mints and seizures that would send tokens to the token contract’s own address.
Where Denim fits in Base’s upgrade history
Denim follows three independent upgrades implemented earlier in 2026:
- Azul: introduced a new client stack and multiproof system.
- Beryl: introduced the B20 token standard.
- Cobalt: added conditional transactions and expanded B20 compliance features.
These are Base’s first four independent upgrades since its 2023 launch. The announcement documents protocol changes; it does not establish adoption or market impact.
Original publication time: November 6, 2026, at 04:00 UTC+08:00 (November 5, 2026, at 20:00 UTC).