pending block tag — eth_getBlockByNumber, eth_call, eth_getBalance, eth_getTransactionCount, eth_getCode, eth_getStorageAt, eth_estimateGas — plus eth_getTransactionReceipt, eth_getTransactionByHash, and eth_sendRawTransactionSync for preconfirmed transactions.
See Flashblocks on Optimism for the full guide, including the Optimism vs. Base differences, performance expectations, and a verification snippet.