Base Denim is live on mainnet: five blocks per second, and Flashblocks are gone

What Base announced

Denim is now running on Base. Base's official account posted on 5 November 2026 that "Base Denim is officially live on mainnet", listing native 200ms blocks, BaseTime for millisecond precision and B20 improvements. The post came at 20:02 UTC, after the 18:00 UTC activation time that Base's documentation had set for mainnet.

The upgrade had been running on Base Sepolia, the test network, since 21 October. Base Build first gave 5 November as the mainnet date on 29 October, and we covered both the upgrade and that date in earlier articles.

Five blocks a second, no more Flashblocks

The headline change is speed. According to Base's documentation, Base used to produce one block every two seconds and now produces five complete blocks per second, each with its own block number, hash and receipts. Denim also replaces Flashblocks, the faster preview updates Base previously published inside each two-second block, so apps that relied on Flashblocks have to switch to the normal block and RPC streams.

BaseTime and B20 changes

BaseTime gives contracts the millisecond part of each block's time, while the standard block timestamp still counts whole seconds. RPC responses gain optional millisecond timestamp fields next to the existing ones. For B20 tokens, Denim makes transfers, mints and seizes to the token's own address fail, applies the transfer executor policy to every transfer path, and lets any policy be inverted with a NOT flag.

What it means for users and builders

Most people sending USDC or using apps on Base do not need to do anything; transactions should simply confirm faster. Builders have a real checklist, though. Base's documentation warns that block numbers now advance ten times faster, so timelocks, cooldowns, vesting schedules, deadlines and governance voting periods counted in blocks will run out in a tenth of the intended time. Logic based on block timestamps is unaffected.

Our take

Five blocks a second is a big step for payments and trading apps on Base, where waiting even two seconds is noticeable. The part to watch is contracts that count time in blocks, especially ones that cannot be upgraded. If you want to try Base apps on the faster network, the Base app is linked on this page.