We are upgrading our Base Sepolia and Mainnet infrastructure to v1.5.0 on 2026-10-19 to support the Denim hardfork on Sepolia. This release introduces hardfork support, performance improvements to proof generation and snapshot downloads, and critical bug fixes. Brief interruptions to RPC availability may occur on that date.
Denim moves Base block production from one canonical block every two seconds to five complete canonical blocks per second, each with its own hash, state root, receipts, and forkchoice lifecycle. Denim replaces Flashblocks, so applications using Flashblocks must migrate to canonical block and RPC streams.
The "pending" block tag is also being retired. Denim activates at the protocol level on Sepolia at 18:00 UTC on October 21 — once that timestamp hits on Sepolia, Flashblocks subscriptions and any RPC call using "pending" (eth_getBalance, eth_getTransactionCount, eth_call, eth_estimateGas, eth_simulateV1, eth_getBlockByNumber, eth_getBlockTransactionCountByNumber, eth_getLogs ranges ending at "pending") stop returning preconfirmation data, with no direct equivalent. Replace these calls with normal requests against the latest canonical block before the fork activates. Inventory your Flashblocks subscriptions and "pending"-tag usage now and migrate ahead of October 21 — see the full migration table: https://docs.base.org/upgrades/denim/migrate-from-flashblocks