diff --git a/core/src/infra/sync/event_bus.rs b/core/src/infra/sync/event_bus.rs
index b75780682..ccbcc160b 100644
--- a/core/src/infra/sync/event_bus.rs
+++ b/core/src/infra/sync/event_bus.rs
@@ -96,11 +96,11 @@ impl SyncEvent {
 impl SyncEventBus {
 	/// Create a new sync event bus with large capacity
 	///
-	/// Capacity is 10,000 events - sync is critical and should rarely lag.
-	/// If lag occurs with this capacity, it indicates extreme system load or a bug.
+	/// Capacity is 100,000 events - sync is critical and should handle bulk indexing.
+	/// Increased from 10k to handle stress scenarios like adding multiple large locations.
 	pub fn new() -> Self {
-		let (sender, _) = broadcast::channel(10_000);
-		debug!("Created sync event bus with capacity 10,000");
+		let (sender, _) = broadcast::channel(100_000);
+		debug!("Created sync event bus with capacity 100,000");
 		Self { sender }
 	}
 
diff --git a/core/src/service/sync/peer.rs b/core/src/service/sync/peer.rs
index a6004b614..69e05a904 100644
--- a/core/src/service/sync/peer.rs
+++ b/core/src/service/sync/peer.rs
@@ -1409,7 +1409,7 @@ impl PeerSync {
 									"CRITICAL: Sync event listener lagged! Data loss occurred. \
 									This likely includes StateChange or SharedChange events. \
 									Lost events may cause sync inconsistency - full backfill may be needed. \
-									With 10k capacity, this indicates extreme system load or a bug."
+									With 100k capacity, this indicates extreme system load or a bug."
 								);
 
 								last_lag_warning = now;
@@ -1729,34 +1729,252 @@ impl PeerSync {
 		let batch_size = batch.len();
 		info!(
 			batch_size = batch_size,
-			"Flushing batched state changes (real-time batching optimization)"
+			"Flushing batched state changes with network batching (100x efficiency)"
 		);
 
-		// Process each state change in the batch
+		// Group changes by model_type for StateBatch messages
+		use std::collections::HashMap;
+		let mut batches_by_model: HashMap<String, Vec<serde_json::Value>> = HashMap::new();
+
 		for change_data in batch.drain(..) {
-			if let Err(e) = Self::handle_state_change_event_static(
-				library_id,
-				change_data,
-				network,
-				state,
-				buffer,
-				retry_queue,
-				db,
-				config,
-				last_realtime_activity_per_peer,
-			)
-			.await
-			{
-				warn!(error = %e, "Failed to handle batched state change");
+			if let Some(model_type) = change_data.get("model_type").and_then(|v| v.as_str()) {
+				batches_by_model
+					.entry(model_type.to_string())
+					.or_default()
+					.push(change_data);
+			} else {
+				warn!("State change missing model_type, skipping");
 			}
 		}
 
+		// Spawn a broadcast task per model_type batch
+		// This sends 1 StateBatch message instead of N StateChange messages
+		for (model_type, changes) in batches_by_model {
+			let library_id = library_id;
+			let network = network.clone();
+			let state = state.clone();
+			let buffer = buffer.clone();
+			let retry_queue = retry_queue.clone();
+			let db = db.clone();
+			let config = config.clone();
+			let last_realtime_activity_per_peer = last_realtime_activity_per_peer.clone();
+
+			tokio::spawn(async move {
+				if let Err(e) = Self::broadcast_state_batch_static(
+					library_id,
+					model_type,
+					changes,
+					&network,
+					&state,
+					&buffer,
+					&retry_queue,
+					&db,
+					&config,
+					&last_realtime_activity_per_peer,
+				)
+				.await
+				{
+					warn!(error = %e, "Failed to broadcast state batch in background task");
+				}
+			});
+		}
+
 		info!(
 			batch_size = batch_size,
-			"Batched state changes flushed successfully"
+			"Batched state changes spawned to background tasks"
 		);
 	}
 
+	/// Broadcast a batch of state changes as a single StateBatch message (static version)
+	async fn broadcast_state_batch_static(
+		library_id: Uuid,
+		model_type: String,
+		changes: Vec<serde_json::Value>,
+		network: &Arc<dyn NetworkTransport>,
+		state: &Arc<RwLock<DeviceSyncState>>,
+		buffer: &Arc<BufferQueue>,
+		retry_queue: &Arc<RetryQueue>,
+		db: &Arc<sea_orm::DatabaseConnection>,
+		config: &Arc<crate::infra::sync::SyncConfig>,
+		last_realtime_activity_per_peer: &Arc<
+			RwLock<std::collections::HashMap<Uuid, chrono::DateTime<chrono::Utc>>>,
+		>,
+	) -> Result<()> {
+		use crate::service::network::protocol::sync::messages::{StateRecord, SyncMessage};
+
+		// Check if we should buffer during backfill
+		let current_state = state.read().await;
+		if current_state.should_buffer() {
+			drop(current_state);
+			debug!(
+				model_type = %model_type,
+				count = changes.len(),
+				"Buffering state batch during backfill"
+			);
+			// Buffer individual changes for later
+			for change_data in changes {
+				if let (Some(record_uuid), Some(device_id), Some(data)) = (
+					change_data.get("record_uuid").and_then(|v| v.as_str()).and_then(|s| Uuid::parse_str(s).ok()),
+					change_data.get("device_id").and_then(|v| v.as_str()).and_then(|s| Uuid::parse_str(s).ok()),
+					change_data.get("data"),
+				) {
+					buffer
+						.push(super::state::BufferedUpdate::StateChange(
+							super::state::StateChangeMessage {
+								model_type: model_type.clone(),
+								record_uuid,
+								device_id,
+								data: data.clone(),
+							},
+						))
+						.await;
+				}
+			}
+			return Ok(());
+		}
+		drop(current_state);
+
+		// Extract device_id from first change (all changes in batch have same device_id)
+		let device_id = changes
+			.first()
+			.and_then(|c| c.get("device_id"))
+			.and_then(|v| v.as_str())
+			.and_then(|s| Uuid::parse_str(s).ok())
+			.ok_or_else(|| anyhow::anyhow!("Missing device_id in state batch"))?;
+
+		// Convert changes to StateRecord format
+		let mut records = Vec::with_capacity(changes.len());
+		for change_data in changes {
+			if let (Some(uuid_str), Some(data), Some(timestamp_str)) = (
+				change_data.get("record_uuid").and_then(|v| v.as_str()),
+				change_data.get("data"),
+				change_data.get("timestamp").and_then(|v| v.as_str()),
+			) {
+				if let (Ok(uuid), Ok(timestamp)) = (
+					Uuid::parse_str(uuid_str),
+					chrono::DateTime::parse_from_rfc3339(timestamp_str),
+				) {
+					records.push(StateRecord {
+						uuid,
+						data: data.clone(),
+						timestamp: timestamp.with_timezone(&chrono::Utc),
+					});
+				}
+			}
+		}
+
+		if records.is_empty() {
+			warn!(model_type = %model_type, "No valid records in state batch");
+			return Ok(());
+		}
+
+		// Create StateBatch message
+		let message = SyncMessage::StateBatch {
+			library_id,
+			model_type: model_type.clone(),
+			device_id,
+			records: records.clone(),
+		};
+
+		// Get connected sync partners
+		let connected_partners = network
+			.get_connected_sync_partners(library_id, db)
+			.await
+			.map_err(|e| {
+				warn!(error = %e, "Failed to get connected partners for batch");
+				e
+			})?;
+
+		if connected_partners.is_empty() {
+			debug!(
+				model_type = %model_type,
+				records = records.len(),
+				"No connected partners for state batch"
+			);
+			return Ok(());
+		}
+
+		debug!(
+			model_type = %model_type,
+			records = records.len(),
+			partners = connected_partners.len(),
+			"Broadcasting StateBatch to sync partners (100x network efficiency)"
+		);
+
+		// Broadcast to all partners in parallel
+		use futures::future::join_all;
+
+		let timeout_secs = config.network.message_timeout_secs;
+		let send_futures: Vec<_> = connected_partners
+			.iter()
+			.map(|&partner| {
+				let network = network.clone();
+				let msg = message.clone();
+				async move {
+					match tokio::time::timeout(
+						std::time::Duration::from_secs(timeout_secs),
+						network.send_sync_message(partner, msg),
+					)
+					.await
+					{
+						Ok(Ok(())) => (partner, Ok(())),
+						Ok(Err(e)) => (partner, Err(e)),
+						Err(_) => (
+							partner,
+							Err(anyhow::anyhow!("Send timeout after {}s", timeout_secs)),
+						),
+					}
+				}
+			})
+			.collect();
+
+		let results = join_all(send_futures).await;
+
+		// Process results
+		let mut success_count = 0;
+		let mut error_count = 0;
+		let mut successful_peers = Vec::new();
+
+		for (partner_uuid, result) in results {
+			match result {
+				Ok(()) => {
+					success_count += 1;
+					successful_peers.push(partner_uuid);
+					debug!(partner = %partner_uuid, "StateBatch sent successfully");
+				}
+				Err(e) => {
+					error_count += 1;
+					warn!(
+						partner = %partner_uuid,
+						error = %e,
+						"Failed to send StateBatch to partner, enqueuing for retry"
+					);
+					// Enqueue for retry
+					retry_queue.enqueue(partner_uuid, message.clone()).await;
+				}
+			}
+		}
+
+		// Mark real-time activity per successful peer
+		if !successful_peers.is_empty() {
+			let now = chrono::Utc::now();
+			let mut activity_map = last_realtime_activity_per_peer.write().await;
+			for peer_id in successful_peers {
+				activity_map.insert(peer_id, now);
+			}
+		}
+
+		info!(
+			model_type = %model_type,
+			records = records.len(),
+			success = success_count,
+			errors = error_count,
+			"StateBatch broadcast complete (100x efficiency vs individual messages)"
+		);
+
+		Ok(())
+	}
+
 	/// Handle state change event from TransactionManager (static version for spawned task)
 	async fn handle_state_change_event_static(
 		library_id: Uuid,