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 eth_subscribe("newFlashblocks") with eth_subscribe("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 RETH_FB_WEBSOCKET_URL, --flashblocks-url, --max-pending-blocks-depth, and --flashblocks.ping-interval. Additionally, validity transactions with the flashblock_index predicate will be rejected, and it is recommended to use block_number to limit the range.