Apps still using Base’s retired Flashblocks feeds can connect without receiving updates. They need a new data route, not another reconnect.

Coinbase’s Base blockchain retired its Flashblocks data feeds in the Nov. 5 Denim upgrade, requiring apps using them to migrate. The old WebSocket endpoints still accept connections but no longer deliver data, according to Base’s migration instructions.

Denim activated on mainnet at 18:00 UTC on Nov. 5. Base’s upgrade overview describes complete canonical blocks every 200 milliseconds, each with its own hash, state root and receipts. These are the chain’s blocks rather than previews of a block still being built.

The compatibility trap is that an open connection no longer establishes that an app is receiving updates. Reconnecting to a retired Flashblocks endpoint leaves the underlying integration problem unresolved.

Denim retired Flashblocks. Apps must move their data route to canonical block and RPC streams.

Replace the Flashblocks data route and review what pending-state requests now return.

Schematic routes, not measured traffic or transaction-inclusion latency. Canonical block inclusion remains separate from Ethereum finality.

Schematic data routes, not a traffic measurement or latency scale. Rectangles represent complete canonical blocks; arrows identify the replacement data route, with no implied transaction-inclusion guarantee.

Schematic routes, not measured traffic or transaction-inclusion latency. Canonical block inclusion remains separate from Ethereum finality.

Base directs developers to replace Flashblocks connections with subscriptions through a WebSocket-capable RPC provider or their own node. Its replacement map has three main subscription changes:

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