Coinbase

The Base blockchain network implemented its Denim upgrade on November 5 at 18:00 UTC, retiring the older Flashblocks data feeds. Following this release, developers utilizing these feeds must migrate their applications. According to migration instructions provided by Base, the old WebSocket endpoints continue to accept connections, but they no longer deliver streaming data, creating a compatibility trap where an open connection does not guarantee that an application is receiving updates.

The Denim upgrade retired Flashblocks, requiring developers to migrate their data subscriptions immediately.

Base now instructs developers to replace their Flashblocks connections using subscriptions through a WebSocket-capable remote procedure call provider or their own node. Additionally, developers must review application behavior regarding the pending block tag. Although the network still accepts this tag, it now resolves to the latest canonical block rather than exposing previous preconfirmation state.

Transaction handling has also changed. Applications can still poll for receipts, but those receipts only become available once a transaction enters a canonical block arriving every 200 milliseconds. Preconfirmed transaction results are no longer accessible. Furthermore, a notice updated on November 5 mentioned an ongoing investigation into periodic transaction inclusion delays and a higher than expected rate of empty blocks.

Why it matters This upgrade affects developers building on the Base network who must update their integrations to avoid broken data feeds. Applications that fail to migrate risk relying on outdated assumptions about pending states and preconfirmed receipts.