Optimism speeds up to 200 ms subblocks but warns of data feed gaps
Optimism cuts subblock time to 200 ms with a compatibility warning
Optimism, a layer-2 network built on Ethereum that processes transactions faster and cheaper, is reducing its subblock time from 250 milliseconds to 200 ms. The change began rolling out on August 31.
Subblocks, previously called Flashblocks, are quick updates sent by the network’s sequencer while it builds a full block. They give apps early feedback before a block is finalized.
Four payload fields now return zero values
As part of the update, four fields in the streamed payload will still appear but will no longer carry usable data. According to Optimism’s migration notice, state_root, block_hash, and withdrawals_root will show as all-zero values, while withdrawals will be an empty list. Other fields, such as receipts_root and logs_bloom, will still contain real data.
The payload type remains unchanged, so software can keep parsing the stream without errors. This makes the change easy to overlook for systems that assume all fields are valid if the stream decodes successfully.
Who needs to act
Optimism states that direct stream consumers and RPC providers that forward raw fields must audit their systems. They need to identify any use of the four affected fields, treat the placeholder values as unavailable, and prevent them from reaching downstream systems like state, balances, or proof inputs. Providers relaying raw payloads must also inform their users.
Most applications connect through a subblocks-aware RPC provider and use standard Ethereum methods, which are safer. A properly configured provider maintains its own state view, so calls like eth_getBalance can return derived preconfirmed data without relying on the zeroed fields.
Rollout status and provider updates
Optimism notes the August 31 target may shift, and the rollout is gradual with no set completion time. Its status page showed no incidents at the time of the report. Provider documentation, such as from Alchemy and QuickNode, already reflects the 200 ms updates for Optimism Mainnet and testnet endpoints.
What is confirmed
- OP Mainnet is targeting 200 ms subblocks, down from 250 ms.
- Four payload fields (
state_root,block_hash,withdrawals_root,withdrawals) will return zero or empty values. - The payload type remains
ExecutionPayloadFlashblockDeltaV1, so streams remain parseable. - Direct stream consumers and RPC providers must audit and adjust their systems.
- The rollout is gradual, with no fixed completion date.
Why this matters
The speed improvement could benefit apps relying on fast preconfirmations. However, the zeroed fields introduce a silent risk: systems that do not audit their data handling may pass invalid values downstream, potentially affecting state or proof calculations.
