Base Activates Denim Upgrade, Cutting Block Times to 200ms

Base activated Denim, its fourth major upgrade, on mainnet on 5 November at 18:00 UTC, trading two-second blocks for five canonical blocks every second. Each 200-millisecond block has its own block number, hash, state root, receipts and forkchoice lifecycle, so a Base block now works the way a block does on Ethereum, just ten times as often.

Base's own documentation for the upgrade sets out what changed. When those pages were read, the mainnet rollout was still listed as "planning" and the client versions required to run a mainnet node were marked "not yet published," and no on-chain check of the exact activation time was available. Reporting around the 5 November date treats Denim as live.

Key Facts

• Base moved from one block every two seconds to five complete blocks per second, each with its own hash, state root, receipts and forkchoice lifecycle, per the Denim overview.
• Denim switches off Flashblocks, the 200ms preconfirmation layer live since July 2025. Apps reading those streams or the "pending" tag must move to canonical block feeds.
• block.number now advances ten times faster in wall-clock time, while block.timestamp still advances in whole seconds.
• Horizen's L3, which settles to Base, says it cannot follow the change and stops accepting user transactions about 40 minutes after activation.
• Gas per block falls from about 400 million to about 40 million, holding throughput near 200 million gas per second.

Flashblocks Are Gone, So Some Apps Must Move

Flashblocks went live on Base in July 2025 as a way to squeeze faster signals out of a two-second block. It streamed 200ms preconfirmations inside the canonical block, which developers read through the newFlashblocks or pendingLogs subscriptions, or the pending block tag.

Denim makes preconfirmations redundant, because the blocks themselves now arrive every 200ms. Base switches the feature off, and the replacements return canonical data from the new blocks rather than preconfirmed or pending data. The migration guide says the pending tag and the Flashblocks preconfirmation state have no direct equivalent after the upgrade.

Any app, bot or indexer still pointed at those streams has to be repointed at standard canonical feeds. Most users will never see the change, until an app that skipped it serves stale or missing data.

Block Numbers Now Tick Ten Times Faster

Because production went from one block every two seconds to five a second, block.number moves ten times faster in wall-clock time. block.timestamp does not: it still advances in whole seconds.

Anything a contract counts in blocks runs ten times faster as a result. Timelocks, vesting schedules and governance voting windows written in blocks will elapse roughly ten times sooner than intended. A one-hour cooldown set at 1,800 blocks would lapse in about six minutes. Immutable contracts cannot be retuned, so the contracts that got this wrong cannot simply be patched.

BaseTime Adds a Millisecond Clock, B20 Rules Tighten

Denim adds onchain millisecond time through a BaseTime predeploy. A BaseTime metadata deposit supplies the sub-second part of each block's timestamp, so a contract can read the millisecond component of the current block while EVM block.timestamp stays seconds-based. That gives contracts a finer clock for order expirations, auction deadlines and similar timing logic.

Denim also tightens the rules around B20 tokens: transfers, mints and seizes to a token's own address now revert, TRANSFER_EXECUTOR_POLICY applies to every transfer path, and any policy can be inverted with a NOT flag. The change follows Azul, Beryl and Cobalt in Base's line since it left Optimism's Superchain, a run we covered when Cobalt added conditional transactions and new B20 rules.

Throughput Holds Flat, RPC Bills May Not

Denim changes latency, not capacity. The gas limit per block drops by the same factor as the block time, from about 400 million per two-second block to about 40 million per 200ms block, keeping throughput near 200 million gas per second, according to the RPC provider Dwellir.

The block count tells the other half of the story. Base produces 43,200 blocks a day at two-second spacing; at 200ms it will produce 432,000, with newHeads events rising from 0.5 a second to 5. Anything that runs once per block, including indexers, bots, oracles, keepers and block explorers, makes ten times the calls, so per-block RPC bills can rise roughly tenfold.

Native transaction batching and gas sponsorship are not part of Denim. They belong to the separate Everest upgrade, whose activation dates are still unset.

Horizen's L3 Shuts Down About 40 Minutes After Activation

Not every chain that settles to Base can follow the change. Horizen says its OP Stack L3 cannot adapt, and that about 40 minutes after Denim activates the chain can no longer include user transactions, permanently.

In its own notice, Horizen says its infrastructure provider confirmed there is no fix, and that it set the bridging cutoff a day before the hard shutdown so the snapshot would be clean and nothing would be in flight when the chain stops. Bridging from the Horizen L3 back to Base closed on 4 November at 13:00 UTC, when the snapshot was taken. Denim then activates on 5 November at 18:00 UTC. The snapshot is due around 7 November for review, and from about 15 November the DAO distributes remaining balances on Base.