# SynchronizationState Kernel-internal synchronization phase, passed to [`blockTip`](/documentation/BitcoinKernel/NotificationCallbacks/blockTip) and [`headerTip`](/documentation/BitcoinKernel/NotificationCallbacks/headerTip) on every tip update. ``` enum SynchronizationState ``` ## Overview Lets observers distinguish “we’re still catching up” events (when tip updates should not trigger user-visible notifications) from steady-state events. > Important: This is **distinct from** ``doc://BitcoinKernel/documentation/BitcoinKernel/BlockchainSync/Update/State-swift.enum`` > — they solve different problems. `SynchronizationState` is the > kernel’s internal IBD-or-not flag (relevant to notification callback > consumers); `BlockchainSync.Update.State` is the sync engine’s own > lifecycle enum (relevant to sync-sequence consumers). Maps to `btck_SynchronizationState` constants in the kernel C API.