Base goes live with Denim: 200ms canonical blocks, Flashblocks retired

Base said on Nov. 5, 2026 that its fourth independent network upgrade, Denim, is live on mainnet. The Coinbase-incubated Layer 2 now produces a full canonical block every 200 milliseconds — five per second — and retires the Flashblocks pending-state stream that filled the old two-second gap between blocks, according to Base's engineering blog.

What Denim changes

Before Denim, Base produced one canonical block every two seconds and used Flashblocks to stream a preview of the block still being built. Denim replaces that model with native 200ms blocks. Each block's full timestamp is exactly 200ms after its parent, and the protocol validates that progression, Base wrote. Including a transaction in a 200ms block does not by itself make it final: like every Base block, it becomes safe when its batch is posted to Ethereum and final when Ethereum finalizes that batch.

The Block reported that applications which previously relied on Flashblocks must migrate to standard canonical block subscriptions. Base's migration table maps eth_subscribe("newFlashblocks") to eth_subscribe("newHeads"), and drops Flashblocks-aware "pending" semantics for balance and call RPCs.

BaseTime and B20

Denim also ships BaseTime: a predeploy at 0x4200…0030 that exposes millisecond Unix time so contracts can expire orders, stream rewards or accrue interest at 200ms resolution. Ethereum-compatible block.timestamp stays in whole seconds; new optional RPC fields such as timestampMs expose the authenticated millisecond clock.

On the token side, Denim adds a NOT operator for reusable B20 compliance lists, extends TRANSFER_EXECUTOR_POLICY to every transfer path (including holder-initiated transfer), and reverts transfers, mints or seizures that would send tokens to the token contract's own address with InvalidReceiver.

Base warned that block.number now advances ten times faster in wall-clock time. Contracts that treat block counts as durations — timelocks, vesting, per-block rate limits, default ERC20Votes clocks — need a review; block.timestamp is unchanged.