Base disables Flashblocks, subscriptions and pending statuses no longer return data

Base has disabled Flashblocks in the Denim upgrade, switching to generating a complete standard block every 200 milliseconds. Denim was activated on Base Sepolia on October 21, 2026, at 18:00 UTC, and on the Base mainnet on November 5 at 18:00 UTC. After activation, Base stopped producing Flashblocks on both networks, and Flashblocks subscriptions, WebSocket streams, and pending states will no longer return data.

The official documentation states that endpoints like wss://mainnet.flashblocks.base.org/ws will still accept connections but will no longer push any data. Developers need to replace ethsubscribe("newFlashblocks") with ethsubscribe("newHeads"), replace pendingLogs with logs, and for newFlashblockTransactions, switch to pulling transactions by standard blocks after using newHeads; RPC calls using the "pending" block tag should be changed to read the latest standard block and state.

Regarding node configuration, mainnet nodes must be upgraded to base/base v1.5.1 or higher, and Sepolia nodes must be v1.5.0 or higher, while removing settings such as RETHFBWEBSOCKETURL, --flashblocks-url, --max-pending-blocks-depth, and --flashblocks.ping-interval. Additionally, validity transactions with the flashblockindex predicate will be rejected, and it is recommended to use block_number to limit the range.