Base Disables Flashblocks, Ending Subscription and Pending-State Data

According to ChainCatcher citing official documentation, Base disabled Flashblocks as part of the Denim upgrade, switching to producing a complete canonical block every 200 milliseconds. Denim activated on Base Sepolia on October 21, 2026, at 18:00 UTC, and on Base mainnet on November 5, 2026, at 18:00 UTC. After activation, Flashblocks subscriptions, WebSocket streams, and pending-state queries no longer return data, although the endpoints still accept connections. Developers should replace `eth_subscribe("newFlashblocks")` with `eth_subscribe("newHeads")` and `pendingLogs` with `logs`. They should use `newHeads` and fetch transactions from canonical blocks instead of using `newFlashblockTransactions`. RPC calls using the `pending` block tag should read the latest canonical block and state. Mainnet nodes must run `base/base` v1.5.1 or later, while Sepolia nodes must run v1.5.0 or later. Operators should remove the `RETH_FB_WEBSOCKET_URL`, `--flashblocks-url`, `--max-pending-blocks-depth`, and `--flashblocks.ping-interval` settings. Validity transactions using the `flashblock_index` predicate will be rejected; the documentation recommends using a `block_number` range instead.