Subblocks go live on OP Sepolia Monday, Aug 17.
Preconfirmations move from 250ms to 200ms.
Four payload fields are set to their zero value:
- state_root
- block_hash
- withdrawals_root
- withdrawals to their zero value
For teams consuming the subblock stream directly:
-
Upgrade 19, the Karst hard fork, is scheduled to activate on Mainnet OP Stack chains Wed, Jul 8, 2026 at 16:00:01 UTC. Please refer to the notice page for full details and required actions.
