Optimism is targeting 200 millisecond subblocks on OP Mainnet, reducing the preconfirmation interval from 250 milliseconds in a rolling change targeted for August 31. Subblocks, formerly called Flashblocks, are incremental updates the sequencer sends while building a normal block, providing applications feedback before that block is finalized.
The 20% speedup introduces a compatibility consideration. Four fields will remain in each streamed payload but return zero values: state_root, block_hash, and withdrawals_root will be all-zero, while withdrawals will be an empty list. The payload type remains ExecutionPayloadFlashblockDeltaV1, allowing software to continue parsing the stream without errors.
Integration Requirements
Direct stream consumers and RPC providers must audit systems to prevent the placeholder values from entering downstream state calculations, balances, or proof inputs. Applications using subblocks-aware RPC providers with standard Ethereum methods can derive preconfirmed state by executing transactions carried in the stream, reducing the audit burden.
Other fields including receipts_root and logs_bloom will still contain real values. Optimism's integration guide advises treating the zeroed state root and block hash as absent data rather than valid values.
Alchemy and QuickNode have updated their provider documentation to reflect the 200 millisecond update cadence on Optimism Mainnet and Sepolia. Optimism indicated the August 31 target may shift and the rollout is gradual, with no documented network-wide completion time.
