# BlockchainSync.Updates A single-consumer `AsyncSequence` of [`BlockchainSync.Update`](/documentation/BitcoinKernel/BlockchainSync/Update) values emitted as the sync engine drives the chainstate forward. ``` struct Updates ``` ## Overview Backed by an [`AsyncStream`](https://developer.apple.com/documentation/swift/asyncstream) with `.bufferingNewest(64)` — under a slow consumer, mid-sync updates may be dropped, but the initial [`BlockchainSync.Update.State.preparing`](/documentation/BitcoinKernel/BlockchainSync/Update/State-swift.enum/preparing) and the terminal [`BlockchainSync.Update.State.finished`](/documentation/BitcoinKernel/BlockchainSync/Update/State-swift.enum/finished) / [`BlockchainSync.Update.State.failed(_:)`](/documentation/BitcoinKernel/BlockchainSync/Update/State-swift.enum/failed(_:)) are always delivered. > Note: Iterating the same `Updates` value twice starts an independent > sync run on each iteration. That’s rarely what you want; store a > single `Updates` value and iterate it once.