diff --git a/Cargo.lock b/Cargo.lock
index ffdc736830..18950cdb82 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1217,6 +1217,7 @@ version = "0.1.0"
 dependencies = [
  "anyhow",
  "client",
+ "clock",
  "collections",
  "db",
  "feature_flags",
@@ -1530,6 +1531,7 @@ dependencies = [
  "tracing-subscriber",
  "unindent",
  "util",
+ "uuid 1.4.1",
  "workspace",
 ]
 
diff --git a/crates/channel/src/channel_buffer.rs b/crates/channel/src/channel_buffer.rs
index a03eb1f1b5..a097cc5467 100644
--- a/crates/channel/src/channel_buffer.rs
+++ b/crates/channel/src/channel_buffer.rs
@@ -2,14 +2,17 @@ use crate::Channel;
 use anyhow::Result;
 use client::{Client, Collaborator, UserStore};
 use collections::HashMap;
-use gpui::{AppContext, AsyncAppContext, Entity, ModelContext, ModelHandle};
+use gpui::{AppContext, AsyncAppContext, Entity, ModelContext, ModelHandle, Task};
+use language::proto::serialize_version;
 use rpc::{
     proto::{self, PeerId},
     TypedEnvelope,
 };
-use std::sync::Arc;
+use std::{sync::Arc, time::Duration};
 use util::ResultExt;
 
+const ACKNOWLEDGE_DEBOUNCE_INTERVAL: Duration = Duration::from_millis(250);
+
 pub(crate) fn init(client: &Arc<Client>) {
     client.add_model_message_handler(ChannelBuffer::handle_update_channel_buffer);
     client.add_model_message_handler(ChannelBuffer::handle_update_channel_buffer_collaborators);
@@ -24,11 +27,13 @@ pub struct ChannelBuffer {
     buffer_epoch: u64,
     client: Arc<Client>,
     subscription: Option<client::Subscription>,
+    acknowledge_task: Option<Task<Result<()>>>,
 }
 
 pub enum ChannelBufferEvent {
     CollaboratorsChanged,
     Disconnected,
+    BufferEdited,
 }
 
 impl Entity for ChannelBuffer {
@@ -36,6 +41,9 @@ impl Entity for ChannelBuffer {
 
     fn release(&mut self, _: &mut AppContext) {
         if self.connected {
+            if let Some(task) = self.acknowledge_task.take() {
+                task.detach();
+            }
             self.client
                 .send(proto::LeaveChannelBuffer {
                     channel_id: self.channel.id,
@@ -81,6 +89,7 @@ impl ChannelBuffer {
                 client,
                 connected: true,
                 collaborators: Default::default(),
+                acknowledge_task: None,
                 channel,
                 subscription: Some(subscription.set_model(&cx.handle(), &mut cx.to_async())),
                 user_store,
@@ -159,19 +168,45 @@ impl ChannelBuffer {
         &mut self,
         _: ModelHandle<language::Buffer>,
         event: &language::Event,
-        _: &mut ModelContext<Self>,
+        cx: &mut ModelContext<Self>,
     ) {
-        if let language::Event::Operation(operation) = event {
-            let operation = language::proto::serialize_operation(operation);
-            self.client
-                .send(proto::UpdateChannelBuffer {
-                    channel_id: self.channel.id,
-                    operations: vec![operation],
-                })
-                .log_err();
+        match event {
+            language::Event::Operation(operation) => {
+                let operation = language::proto::serialize_operation(operation);
+                self.client
+                    .send(proto::UpdateChannelBuffer {
+                        channel_id: self.channel.id,
+                        operations: vec![operation],
+                    })
+                    .log_err();
+            }
+            language::Event::Edited => {
+                cx.emit(ChannelBufferEvent::BufferEdited);
+            }
+            _ => {}
         }
     }
 
+    pub fn acknowledge_buffer_version(&mut self, cx: &mut ModelContext<'_, ChannelBuffer>) {
+        let buffer = self.buffer.read(cx);
+        let version = buffer.version();
+        let buffer_id = buffer.remote_id();
+        let client = self.client.clone();
+        let epoch = self.epoch();
+
+        self.acknowledge_task = Some(cx.spawn_weak(|_, cx| async move {
+            cx.background().timer(ACKNOWLEDGE_DEBOUNCE_INTERVAL).await;
+            client
+                .send(proto::AckBufferOperation {
+                    buffer_id,
+                    epoch,
+                    version: serialize_version(&version),
+                })
+                .ok();
+            Ok(())
+        }));
+    }
+
     pub fn epoch(&self) -> u64 {
         self.buffer_epoch
     }
diff --git a/crates/channel/src/channel_chat.rs b/crates/channel/src/channel_chat.rs
index 8e03a3b6fd..5b32d67f63 100644
--- a/crates/channel/src/channel_chat.rs
+++ b/crates/channel/src/channel_chat.rs
@@ -1,4 +1,4 @@
-use crate::Channel;
+use crate::{Channel, ChannelStore};
 use anyhow::{anyhow, Result};
 use client::{
     proto,
@@ -16,7 +16,9 @@ use util::{post_inc, ResultExt as _, TryFutureExt};
 pub struct ChannelChat {
     channel: Arc<Channel>,
     messages: SumTree<ChannelMessage>,
+    channel_store: ModelHandle<ChannelStore>,
     loaded_all_messages: bool,
+    last_acknowledged_id: Option<u64>,
     next_pending_message_id: usize,
     user_store: ModelHandle<UserStore>,
     rpc: Arc<Client>,
@@ -77,6 +79,7 @@ impl Entity for ChannelChat {
 impl ChannelChat {
     pub async fn new(
         channel: Arc<Channel>,
+        channel_store: ModelHandle<ChannelStore>,
         user_store: ModelHandle<UserStore>,
         client: Arc<Client>,
         mut cx: AsyncAppContext,
@@ -94,11 +97,13 @@ impl ChannelChat {
             let mut this = Self {
                 channel,
                 user_store,
+                channel_store,
                 rpc: client,
                 outgoing_messages_lock: Default::default(),
                 messages: Default::default(),
                 loaded_all_messages,
                 next_pending_message_id: 0,
+                last_acknowledged_id: None,
                 rng: StdRng::from_entropy(),
                 _subscription: subscription.set_model(&cx.handle(), &mut cx.to_async()),
             };
@@ -219,6 +224,26 @@ impl ChannelChat {
         false
     }
 
+    pub fn acknowledge_last_message(&mut self, cx: &mut ModelContext<Self>) {
+        if let ChannelMessageId::Saved(latest_message_id) = self.messages.summary().max_id {
+            if self
+                .last_acknowledged_id
+                .map_or(true, |acknowledged_id| acknowledged_id < latest_message_id)
+            {
+                self.rpc
+                    .send(proto::AckChannelMessage {
+                        channel_id: self.channel.id,
+                        message_id: latest_message_id,
+                    })
+                    .ok();
+                self.last_acknowledged_id = Some(latest_message_id);
+                self.channel_store.update(cx, |store, cx| {
+                    store.acknowledge_message_id(self.channel.id, latest_message_id, cx);
+                });
+            }
+        }
+    }
+
     pub fn rejoin(&mut self, cx: &mut ModelContext<Self>) {
         let user_store = self.user_store.clone();
         let rpc = self.rpc.clone();
diff --git a/crates/channel/src/channel_store.rs b/crates/channel/src/channel_store.rs
index f0f66f4839..db6d5f42c5 100644
--- a/crates/channel/src/channel_store.rs
+++ b/crates/channel/src/channel_store.rs
@@ -43,8 +43,8 @@ pub type ChannelData = (Channel, ChannelPath);
 pub struct Channel {
     pub id: ChannelId,
     pub name: String,
-    pub has_note_changed: bool,
-    pub has_new_messages: bool,
+    pub unseen_note_version: Option<(u64, clock::Global)>,
+    pub unseen_message_id: Option<u64>,
 }
 
 #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Serialize, Deserialize)]
@@ -201,34 +201,60 @@ impl ChannelStore {
     ) -> Task<Result<ModelHandle<ChannelBuffer>>> {
         let client = self.client.clone();
         let user_store = self.user_store.clone();
-        let open_channel_buffer = self.open_channel_resource(
+        self.open_channel_resource(
             channel_id,
             |this| &mut this.opened_buffers,
             |channel, cx| ChannelBuffer::new(channel, client, user_store, cx),
             cx,
-        );
-        cx.spawn(|this, mut cx| async move {
-            let buffer = open_channel_buffer.await?;
-            this.update(&mut cx, |this, cx| {
-                this.channel_index.clear_note_changed(channel_id);
-                cx.notify();
-            });
-            Ok(buffer)
-        })
+        )
     }
 
     pub fn has_channel_buffer_changed(&self, channel_id: ChannelId) -> Option<bool> {
         self.channel_index
             .by_id()
             .get(&channel_id)
-            .map(|channel| channel.has_note_changed)
+            .map(|channel| channel.unseen_note_version.is_some())
     }
 
     pub fn has_new_messages(&self, channel_id: ChannelId) -> Option<bool> {
         self.channel_index
             .by_id()
             .get(&channel_id)
-            .map(|channel| channel.has_new_messages)
+            .map(|channel| channel.unseen_message_id.is_some())
+    }
+
+    pub fn notes_changed(
+        &mut self,
+        channel_id: ChannelId,
+        epoch: u64,
+        version: &clock::Global,
+        cx: &mut ModelContext<Self>,
+    ) {
+        self.channel_index.note_changed(channel_id, epoch, version);
+        cx.notify();
+    }
+
+    pub fn acknowledge_message_id(
+        &mut self,
+        channel_id: ChannelId,
+        message_id: u64,
+        cx: &mut ModelContext<Self>,
+    ) {
+        self.channel_index
+            .acknowledge_message_id(channel_id, message_id);
+        cx.notify();
+    }
+
+    pub fn acknowledge_notes_version(
+        &mut self,
+        channel_id: ChannelId,
+        epoch: u64,
+        version: &clock::Global,
+        cx: &mut ModelContext<Self>,
+    ) {
+        self.channel_index
+            .acknowledge_note_version(channel_id, epoch, version);
+        cx.notify();
     }
 
     pub fn open_channel_chat(
@@ -238,20 +264,13 @@ impl ChannelStore {
     ) -> Task<Result<ModelHandle<ChannelChat>>> {
         let client = self.client.clone();
         let user_store = self.user_store.clone();
-        let open_channel_chat = self.open_channel_resource(
+        let this = cx.handle();
+        self.open_channel_resource(
             channel_id,
             |this| &mut this.opened_chats,
-            |channel, cx| ChannelChat::new(channel, user_store, client, cx),
+            |channel, cx| ChannelChat::new(channel, this, user_store, client, cx),
             cx,
-        );
-        cx.spawn(|this, mut cx| async move {
-            let chat = open_channel_chat.await?;
-            this.update(&mut cx, |this, cx| {
-                this.channel_index.clear_message_changed(channel_id);
-                cx.notify();
-            });
-            Ok(chat)
-        })
+        )
     }
 
     /// Asynchronously open a given resource associated with a channel.
@@ -811,8 +830,8 @@ impl ChannelStore {
                     Arc::new(Channel {
                         id: channel.id,
                         name: channel.name,
-                        has_note_changed: false,
-                        has_new_messages: false,
+                        unseen_note_version: None,
+                        unseen_message_id: None,
                     }),
                 ),
             }
@@ -822,8 +841,8 @@ impl ChannelStore {
             || !payload.delete_channels.is_empty()
             || !payload.insert_edge.is_empty()
             || !payload.delete_edge.is_empty()
-            || !payload.notes_changed.is_empty()
-            || !payload.new_messages.is_empty();
+            || !payload.unseen_channel_messages.is_empty()
+            || !payload.unseen_channel_buffer_changes.is_empty();
 
         if channels_changed {
             if !payload.delete_channels.is_empty() {
@@ -850,12 +869,20 @@ impl ChannelStore {
                 index.insert(channel)
             }
 
-            for id_changed in payload.notes_changed {
-                index.note_changed(id_changed);
+            for unseen_buffer_change in payload.unseen_channel_buffer_changes {
+                let version = language::proto::deserialize_version(&unseen_buffer_change.version);
+                index.note_changed(
+                    unseen_buffer_change.channel_id,
+                    unseen_buffer_change.epoch,
+                    &version,
+                );
             }
 
-            for id_changed in payload.new_messages {
-                index.new_messages(id_changed);
+            for unseen_channel_message in payload.unseen_channel_messages {
+                index.new_messages(
+                    unseen_channel_message.channel_id,
+                    unseen_channel_message.message_id,
+                );
             }
 
             for edge in payload.insert_edge {
diff --git a/crates/channel/src/channel_store/channel_index.rs b/crates/channel/src/channel_store/channel_index.rs
index 513e20e3a7..2a93ca6573 100644
--- a/crates/channel/src/channel_store/channel_index.rs
+++ b/crates/channel/src/channel_store/channel_index.rs
@@ -39,17 +39,38 @@ impl ChannelIndex {
         }
     }
 
-    pub fn clear_note_changed(&mut self, channel_id: ChannelId) {
+    pub fn acknowledge_note_version(
+        &mut self,
+        channel_id: ChannelId,
+        epoch: u64,
+        version: &clock::Global,
+    ) {
         if let Some(channel) = self.channels_by_id.get_mut(&channel_id) {
-            Arc::make_mut(channel).has_note_changed = false;
+            let channel = Arc::make_mut(channel);
+            if let Some((unseen_epoch, unseen_version)) = &channel.unseen_note_version {
+                if epoch > *unseen_epoch
+                    || epoch == *unseen_epoch && version.observed_all(unseen_version)
+                {
+                    channel.unseen_note_version = None;
+                }
+            }
         }
     }
 
-    pub fn clear_message_changed(&mut self, channel_id: ChannelId) {
+    pub fn acknowledge_message_id(&mut self, channel_id: ChannelId, message_id: u64) {
         if let Some(channel) = self.channels_by_id.get_mut(&channel_id) {
-            Arc::make_mut(channel).has_new_messages = false;
+            let channel = Arc::make_mut(channel);
+            if let Some(unseen_message_id) = channel.unseen_message_id {
+                if message_id >= unseen_message_id {
+                    channel.unseen_message_id = None;
+                }
+            }
         }
     }
+
+    pub fn note_changed(&mut self, channel_id: ChannelId, epoch: u64, version: &clock::Global) {
+        insert_note_changed(&mut self.channels_by_id, channel_id, epoch, version);
+    }
 }
 
 impl Deref for ChannelIndex {
@@ -88,15 +109,14 @@ impl<'a> ChannelPathsInsertGuard<'a> {
         }
     }
 
-    pub fn note_changed(&mut self, channel_id: ChannelId) {
-        if let Some(channel) = self.channels_by_id.get_mut(&channel_id) {
-            Arc::make_mut(channel).has_note_changed = true;
-        }
+    pub fn note_changed(&mut self, channel_id: ChannelId, epoch: u64, version: &clock::Global) {
+        insert_note_changed(&mut self.channels_by_id, channel_id, epoch, &version);
     }
 
-    pub fn new_messages(&mut self, channel_id: ChannelId) {
+    pub fn new_messages(&mut self, channel_id: ChannelId, message_id: u64) {
         if let Some(channel) = self.channels_by_id.get_mut(&channel_id) {
-            Arc::make_mut(channel).has_new_messages = true;
+            let unseen_message_id = Arc::make_mut(channel).unseen_message_id.get_or_insert(0);
+            *unseen_message_id = message_id.max(*unseen_message_id);
         }
     }
 
@@ -109,8 +129,8 @@ impl<'a> ChannelPathsInsertGuard<'a> {
                 Arc::new(Channel {
                     id: channel_proto.id,
                     name: channel_proto.name,
-                    has_note_changed: false,
-                    has_new_messages: false,
+                    unseen_note_version: None,
+                    unseen_message_id: None,
                 }),
             );
             self.insert_root(channel_proto.id);
@@ -186,3 +206,21 @@ fn channel_path_sorting_key<'a>(
     path.iter()
         .map(|id| Some(channels_by_id.get(id)?.name.as_str()))
 }
+
+fn insert_note_changed(
+    channels_by_id: &mut BTreeMap<ChannelId, Arc<Channel>>,
+    channel_id: u64,
+    epoch: u64,
+    version: &clock::Global,
+) {
+    if let Some(channel) = channels_by_id.get_mut(&channel_id) {
+        let unseen_version = Arc::make_mut(channel)
+            .unseen_note_version
+            .get_or_insert((0, clock::Global::new()));
+        if epoch > unseen_version.0 {
+            *unseen_version = (epoch, version.clone());
+        } else {
+            unseen_version.1.join(&version);
+        }
+    }
+}
diff --git a/crates/client/src/client.rs b/crates/client/src/client.rs
index 5eae700404..5767ac54b7 100644
--- a/crates/client/src/client.rs
+++ b/crates/client/src/client.rs
@@ -34,7 +34,7 @@ use std::{
     future::Future,
     marker::PhantomData,
     path::PathBuf,
-    sync::{Arc, Weak},
+    sync::{atomic::AtomicU64, Arc, Weak},
     time::{Duration, Instant},
 };
 use telemetry::Telemetry;
@@ -105,7 +105,7 @@ pub fn init(client: &Arc<Client>, cx: &mut AppContext) {
 }
 
 pub struct Client {
-    id: usize,
+    id: AtomicU64,
     peer: Arc<Peer>,
     http: Arc<dyn HttpClient>,
     telemetry: Arc<Telemetry>,
@@ -374,7 +374,7 @@ impl settings::Setting for TelemetrySettings {
 impl Client {
     pub fn new(http: Arc<dyn HttpClient>, cx: &AppContext) -> Arc<Self> {
         Arc::new(Self {
-            id: 0,
+            id: AtomicU64::new(0),
             peer: Peer::new(0),
             telemetry: Telemetry::new(http.clone(), cx),
             http,
@@ -387,17 +387,16 @@ impl Client {
         })
     }
 
-    pub fn id(&self) -> usize {
-        self.id
+    pub fn id(&self) -> u64 {
+        self.id.load(std::sync::atomic::Ordering::SeqCst)
     }
 
     pub fn http_client(&self) -> Arc<dyn HttpClient> {
         self.http.clone()
     }
 
-    #[cfg(any(test, feature = "test-support"))]
-    pub fn set_id(&mut self, id: usize) -> &Self {
-        self.id = id;
+    pub fn set_id(&self, id: u64) -> &Self {
+        self.id.store(id, std::sync::atomic::Ordering::SeqCst);
         self
     }
 
@@ -454,7 +453,7 @@ impl Client {
     }
 
     fn set_status(self: &Arc<Self>, status: Status, cx: &AsyncAppContext) {
-        log::info!("set status on client {}: {:?}", self.id, status);
+        log::info!("set status on client {}: {:?}", self.id(), status);
         let mut state = self.state.write();
         *state.status.0.borrow_mut() = status;
 
@@ -805,6 +804,7 @@ impl Client {
             }
         }
         let credentials = credentials.unwrap();
+        self.set_id(credentials.user_id);
 
         if was_disconnected {
             self.set_status(Status::Connecting, cx);
@@ -1221,7 +1221,7 @@ impl Client {
     }
 
     pub fn send<T: EnvelopedMessage>(&self, message: T) -> Result<()> {
-        log::debug!("rpc send. client_id:{}, name:{}", self.id, T::NAME);
+        log::debug!("rpc send. client_id:{}, name:{}", self.id(), T::NAME);
         self.peer.send(self.connection_id()?, message)
     }
 
@@ -1237,7 +1237,7 @@ impl Client {
         &self,
         request: T,
     ) -> impl Future<Output = Result<TypedEnvelope<T::Response>>> {
-        let client_id = self.id;
+        let client_id = self.id();
         log::debug!(
             "rpc request start. client_id:{}. name:{}",
             client_id,
@@ -1258,7 +1258,7 @@ impl Client {
     }
 
     fn respond<T: RequestMessage>(&self, receipt: Receipt<T>, response: T::Response) -> Result<()> {
-        log::debug!("rpc respond. client_id:{}. name:{}", self.id, T::NAME);
+        log::debug!("rpc respond. client_id:{}. name:{}", self.id(), T::NAME);
         self.peer.respond(receipt, response)
     }
 
@@ -1267,7 +1267,7 @@ impl Client {
         receipt: Receipt<T>,
         error: proto::Error,
     ) -> Result<()> {
-        log::debug!("rpc respond. client_id:{}. name:{}", self.id, T::NAME);
+        log::debug!("rpc respond. client_id:{}. name:{}", self.id(), T::NAME);
         self.peer.respond_with_error(receipt, error)
     }
 
@@ -1336,7 +1336,7 @@ impl Client {
 
         if let Some(handler) = handler {
             let future = handler(subscriber, message, &self, cx.clone());
-            let client_id = self.id;
+            let client_id = self.id();
             log::debug!(
                 "rpc message received. client_id:{}, sender_id:{:?}, type:{}",
                 client_id,
diff --git a/crates/collab/src/db.rs b/crates/collab/src/db.rs
index 13bb3c06e8..e60b7cc33d 100644
--- a/crates/collab/src/db.rs
+++ b/crates/collab/src/db.rs
@@ -439,8 +439,8 @@ pub struct ChannelsForUser {
     pub channels: ChannelGraph,
     pub channel_participants: HashMap<ChannelId, Vec<UserId>>,
     pub channels_with_admin_privileges: HashSet<ChannelId>,
-    pub channels_with_changed_notes: HashSet<ChannelId>,
-    pub channels_with_new_messages: HashSet<ChannelId>,
+    pub unseen_buffer_changes: Vec<proto::UnseenChannelBufferChange>,
+    pub channel_messages: Vec<proto::UnseenChannelMessage>,
 }
 
 #[derive(Debug)]
diff --git a/crates/collab/src/db/queries/buffers.rs b/crates/collab/src/db/queries/buffers.rs
index 78ccd9e54a..c85432f2bb 100644
--- a/crates/collab/src/db/queries/buffers.rs
+++ b/crates/collab/src/db/queries/buffers.rs
@@ -432,7 +432,12 @@ impl Database {
         channel_id: ChannelId,
         user: UserId,
         operations: &[proto::Operation],
-    ) -> Result<(Vec<ConnectionId>, Vec<UserId>)> {
+    ) -> Result<(
+        Vec<ConnectionId>,
+        Vec<UserId>,
+        i32,
+        Vec<proto::VectorClockEntry>,
+    )> {
         self.transaction(move |tx| async move {
             self.check_user_is_channel_member(channel_id, user, &*tx)
                 .await?;
@@ -453,6 +458,7 @@ impl Database {
                 .collect::<Vec<_>>();
 
             let mut channel_members;
+            let max_version;
 
             if !operations.is_empty() {
                 let max_operation = operations
@@ -460,6 +466,11 @@ impl Database {
                     .max_by_key(|op| (op.lamport_timestamp.as_ref(), op.replica_id.as_ref()))
                     .unwrap();
 
+                max_version = vec![proto::VectorClockEntry {
+                    replica_id: *max_operation.replica_id.as_ref() as u32,
+                    timestamp: *max_operation.lamport_timestamp.as_ref() as u32,
+                }];
+
                 // get current channel participants and save the max operation above
                 self.save_max_operation(
                     user,
@@ -492,6 +503,7 @@ impl Database {
                     .await?;
             } else {
                 channel_members = Vec::new();
+                max_version = Vec::new();
             }
 
             let mut connections = Vec::new();
@@ -510,7 +522,7 @@ impl Database {
                 });
             }
 
-            Ok((connections, channel_members))
+            Ok((connections, channel_members, buffer.epoch, max_version))
         })
         .await
     }
@@ -712,12 +724,12 @@ impl Database {
         .await
     }
 
-    pub async fn channels_with_changed_notes(
+    pub async fn unseen_channel_buffer_changes(
         &self,
         user_id: UserId,
         channel_ids: &[ChannelId],
         tx: &DatabaseTransaction,
-    ) -> Result<HashSet<ChannelId>> {
+    ) -> Result<Vec<proto::UnseenChannelBufferChange>> {
         #[derive(Debug, Clone, Copy, EnumIter, DeriveColumn)]
         enum QueryIds {
             ChannelId,
@@ -750,37 +762,45 @@ impl Database {
         }
         drop(rows);
 
-        let last_operations = self
-            .get_last_operations_for_buffers(channel_ids_by_buffer_id.keys().copied(), &*tx)
+        let latest_operations = self
+            .get_latest_operations_for_buffers(channel_ids_by_buffer_id.keys().copied(), &*tx)
             .await?;
 
-        let mut channels_with_new_changes = HashSet::default();
-        for last_operation in last_operations {
-            if let Some(observed_edit) = observed_edits_by_buffer_id.get(&last_operation.buffer_id)
-            {
-                if observed_edit.epoch == last_operation.epoch
-                    && observed_edit.lamport_timestamp == last_operation.lamport_timestamp
-                    && observed_edit.replica_id == last_operation.replica_id
+        let mut changes = Vec::default();
+        for latest in latest_operations {
+            if let Some(observed) = observed_edits_by_buffer_id.get(&latest.buffer_id) {
+                if (
+                    observed.epoch,
+                    observed.lamport_timestamp,
+                    observed.replica_id,
+                ) >= (latest.epoch, latest.lamport_timestamp, latest.replica_id)
                 {
                     continue;
                 }
             }
 
-            if let Some(channel_id) = channel_ids_by_buffer_id.get(&last_operation.buffer_id) {
-                channels_with_new_changes.insert(*channel_id);
+            if let Some(channel_id) = channel_ids_by_buffer_id.get(&latest.buffer_id) {
+                changes.push(proto::UnseenChannelBufferChange {
+                    channel_id: channel_id.to_proto(),
+                    epoch: latest.epoch as u64,
+                    version: vec![proto::VectorClockEntry {
+                        replica_id: latest.replica_id as u32,
+                        timestamp: latest.lamport_timestamp as u32,
+                    }],
+                });
             }
         }
 
-        Ok(channels_with_new_changes)
+        Ok(changes)
     }
 
-    pub async fn get_last_operations_for_buffers(
+    pub async fn get_latest_operations_for_buffers(
         &self,
-        channel_ids: impl IntoIterator<Item = BufferId>,
+        buffer_ids: impl IntoIterator<Item = BufferId>,
         tx: &DatabaseTransaction,
     ) -> Result<Vec<buffer_operation::Model>> {
         let mut values = String::new();
-        for id in channel_ids {
+        for id in buffer_ids {
             if !values.is_empty() {
                 values.push_str(", ");
             }
@@ -795,13 +815,10 @@ impl Database {
             r#"
             SELECT
                 *
-            FROM (
+            FROM
+            (
                 SELECT
-                    buffer_id,
-                    epoch,
-                    lamport_timestamp,
-                    replica_id,
-                    value,
+                    *,
                     row_number() OVER (
                         PARTITION BY buffer_id
                         ORDER BY
@@ -812,17 +829,17 @@ impl Database {
                 FROM buffer_operations
                 WHERE
                     buffer_id in ({values})
-            ) AS operations
+            ) AS last_operations
             WHERE
                 row_number = 1
             "#,
         );
 
         let stmt = Statement::from_string(self.pool.get_database_backend(), sql);
-        let operations = buffer_operation::Model::find_by_statement(stmt)
+        Ok(buffer_operation::Entity::find()
+            .from_raw_sql(stmt)
             .all(&*tx)
-            .await?;
-        Ok(operations)
+            .await?)
     }
 }
 
diff --git a/crates/collab/src/db/queries/channels.rs b/crates/collab/src/db/queries/channels.rs
index 207cca7657..ab31f59541 100644
--- a/crates/collab/src/db/queries/channels.rs
+++ b/crates/collab/src/db/queries/channels.rs
@@ -463,20 +463,20 @@ impl Database {
         }
 
         let channel_ids = graph.channels.iter().map(|c| c.id).collect::<Vec<_>>();
-        let channels_with_changed_notes = self
-            .channels_with_changed_notes(user_id, &channel_ids, &*tx)
+        let channel_buffer_changes = self
+            .unseen_channel_buffer_changes(user_id, &channel_ids, &*tx)
             .await?;
 
-        let channels_with_new_messages = self
-            .channels_with_new_messages(user_id, &channel_ids, &*tx)
+        let unseen_messages = self
+            .unseen_channel_messages(user_id, &channel_ids, &*tx)
             .await?;
 
         Ok(ChannelsForUser {
             channels: graph,
             channel_participants,
             channels_with_admin_privileges,
-            channels_with_changed_notes,
-            channels_with_new_messages,
+            unseen_buffer_changes: channel_buffer_changes,
+            channel_messages: unseen_messages,
         })
     }
 
diff --git a/crates/collab/src/db/queries/messages.rs b/crates/collab/src/db/queries/messages.rs
index 893c1726da..db1252230e 100644
--- a/crates/collab/src/db/queries/messages.rs
+++ b/crates/collab/src/db/queries/messages.rs
@@ -279,12 +279,12 @@ impl Database {
         Ok(())
     }
 
-    pub async fn channels_with_new_messages(
+    pub async fn unseen_channel_messages(
         &self,
         user_id: UserId,
         channel_ids: &[ChannelId],
         tx: &DatabaseTransaction,
-    ) -> Result<collections::HashSet<ChannelId>> {
+    ) -> Result<Vec<proto::UnseenChannelMessage>> {
         let mut observed_messages_by_channel_id = HashMap::default();
         let mut rows = observed_channel_messages::Entity::find()
             .filter(observed_channel_messages::Column::UserId.eq(user_id))
@@ -334,7 +334,7 @@ impl Database {
             .all(&*tx)
             .await?;
 
-        let mut channels_with_new_changes = HashSet::default();
+        let mut changes = Vec::new();
         for last_message in last_messages {
             if let Some(observed_message) =
                 observed_messages_by_channel_id.get(&last_message.channel_id)
@@ -343,10 +343,13 @@ impl Database {
                     continue;
                 }
             }
-            channels_with_new_changes.insert(last_message.channel_id);
+            changes.push(proto::UnseenChannelMessage {
+                channel_id: last_message.channel_id.to_proto(),
+                message_id: last_message.id.to_proto(),
+            });
         }
 
-        Ok(channels_with_new_changes)
+        Ok(changes)
     }
 
     pub async fn remove_channel_message(
diff --git a/crates/collab/src/db/tests/buffer_tests.rs b/crates/collab/src/db/tests/buffer_tests.rs
index 407cc22108..e5d8ab8cf9 100644
--- a/crates/collab/src/db/tests/buffer_tests.rs
+++ b/crates/collab/src/db/tests/buffer_tests.rs
@@ -235,7 +235,7 @@ async fn test_channel_buffers_last_operations(db: &Database) {
         .transaction(|tx| {
             let buffers = &buffers;
             async move {
-                db.get_last_operations_for_buffers([buffers[0].id, buffers[2].id], &*tx)
+                db.get_latest_operations_for_buffers([buffers[0].id, buffers[2].id], &*tx)
                     .await
             }
         })
@@ -299,7 +299,7 @@ async fn test_channel_buffers_last_operations(db: &Database) {
         .transaction(|tx| {
             let buffers = &buffers;
             async move {
-                db.get_last_operations_for_buffers([buffers[1].id, buffers[2].id], &*tx)
+                db.get_latest_operations_for_buffers([buffers[1].id, buffers[2].id], &*tx)
                     .await
             }
         })
@@ -317,7 +317,7 @@ async fn test_channel_buffers_last_operations(db: &Database) {
         .transaction(|tx| {
             let buffers = &buffers;
             async move {
-                db.get_last_operations_for_buffers([buffers[0].id, buffers[1].id], &*tx)
+                db.get_latest_operations_for_buffers([buffers[0].id, buffers[1].id], &*tx)
                     .await
             }
         })
@@ -331,11 +331,11 @@ async fn test_channel_buffers_last_operations(db: &Database) {
         ],
     );
 
-    let changed_channels = db
+    let buffer_changes = db
         .transaction(|tx| {
             let buffers = &buffers;
             async move {
-                db.channels_with_changed_notes(
+                db.unseen_channel_buffer_changes(
                     observer_id,
                     &[
                         buffers[0].channel_id,
@@ -349,31 +349,42 @@ async fn test_channel_buffers_last_operations(db: &Database) {
         })
         .await
         .unwrap();
+
     assert_eq!(
-        changed_channels,
+        buffer_changes,
         [
-            buffers[0].channel_id,
-            buffers[1].channel_id,
-            buffers[2].channel_id,
+            rpc::proto::UnseenChannelBufferChange {
+                channel_id: buffers[0].channel_id.to_proto(),
+                epoch: 0,
+                version: serialize_version(&text_buffers[0].version()),
+            },
+            rpc::proto::UnseenChannelBufferChange {
+                channel_id: buffers[1].channel_id.to_proto(),
+                epoch: 1,
+                version: serialize_version(&text_buffers[1].version()),
+            },
+            rpc::proto::UnseenChannelBufferChange {
+                channel_id: buffers[2].channel_id.to_proto(),
+                epoch: 0,
+                version: serialize_version(&text_buffers[2].version()),
+            },
         ]
-        .into_iter()
-        .collect::<HashSet<_>>()
     );
 
     db.observe_buffer_version(
         buffers[1].id,
         observer_id,
         1,
-        &serialize_version(&text_buffers[1].version()),
+        serialize_version(&text_buffers[1].version()).as_slice(),
     )
     .await
     .unwrap();
 
-    let changed_channels = db
+    let buffer_changes = db
         .transaction(|tx| {
             let buffers = &buffers;
             async move {
-                db.channels_with_changed_notes(
+                db.unseen_channel_buffer_changes(
                     observer_id,
                     &[
                         buffers[0].channel_id,
@@ -387,11 +398,21 @@ async fn test_channel_buffers_last_operations(db: &Database) {
         })
         .await
         .unwrap();
+
     assert_eq!(
-        changed_channels,
-        [buffers[0].channel_id, buffers[2].channel_id,]
-            .into_iter()
-            .collect::<HashSet<_>>()
+        buffer_changes,
+        [
+            rpc::proto::UnseenChannelBufferChange {
+                channel_id: buffers[0].channel_id.to_proto(),
+                epoch: 0,
+                version: serialize_version(&text_buffers[0].version()),
+            },
+            rpc::proto::UnseenChannelBufferChange {
+                channel_id: buffers[2].channel_id.to_proto(),
+                epoch: 0,
+                version: serialize_version(&text_buffers[2].version()),
+            },
+        ]
     );
 
     // Observe an earlier version of the buffer.
@@ -407,11 +428,11 @@ async fn test_channel_buffers_last_operations(db: &Database) {
     .await
     .unwrap();
 
-    let changed_channels = db
+    let buffer_changes = db
         .transaction(|tx| {
             let buffers = &buffers;
             async move {
-                db.channels_with_changed_notes(
+                db.unseen_channel_buffer_changes(
                     observer_id,
                     &[
                         buffers[0].channel_id,
@@ -425,11 +446,21 @@ async fn test_channel_buffers_last_operations(db: &Database) {
         })
         .await
         .unwrap();
+
     assert_eq!(
-        changed_channels,
-        [buffers[0].channel_id, buffers[2].channel_id,]
-            .into_iter()
-            .collect::<HashSet<_>>()
+        buffer_changes,
+        [
+            rpc::proto::UnseenChannelBufferChange {
+                channel_id: buffers[0].channel_id.to_proto(),
+                epoch: 0,
+                version: serialize_version(&text_buffers[0].version()),
+            },
+            rpc::proto::UnseenChannelBufferChange {
+                channel_id: buffers[2].channel_id.to_proto(),
+                epoch: 0,
+                version: serialize_version(&text_buffers[2].version()),
+            },
+        ]
     );
 }
 
diff --git a/crates/collab/src/db/tests/message_tests.rs b/crates/collab/src/db/tests/message_tests.rs
index f3d385e4a0..4966ef1bda 100644
--- a/crates/collab/src/db/tests/message_tests.rs
+++ b/crates/collab/src/db/tests/message_tests.rs
@@ -144,25 +144,32 @@ async fn test_channel_message_new_notification(db: &Arc<Database>) {
         .await
         .unwrap();
 
-    let _ = db
+    let (fourth_message, _, _) = db
         .create_channel_message(channel_2, user, "2_1", OffsetDateTime::now_utc(), 4)
         .await
         .unwrap();
 
     // Check that observer has new messages
-    let channels_with_new_messages = db
+    let unseen_messages = db
         .transaction(|tx| async move {
-            db.channels_with_new_messages(observer, &[channel_1, channel_2], &*tx)
+            db.unseen_channel_messages(observer, &[channel_1, channel_2], &*tx)
                 .await
         })
         .await
         .unwrap();
 
     assert_eq!(
-        channels_with_new_messages,
-        [channel_1, channel_2]
-            .into_iter()
-            .collect::<collections::HashSet<_>>()
+        unseen_messages,
+        [
+            rpc::proto::UnseenChannelMessage {
+                channel_id: channel_1.to_proto(),
+                message_id: third_message.to_proto(),
+            },
+            rpc::proto::UnseenChannelMessage {
+                channel_id: channel_2.to_proto(),
+                message_id: fourth_message.to_proto(),
+            },
+        ]
     );
 
     // Observe the second message
@@ -171,18 +178,25 @@ async fn test_channel_message_new_notification(db: &Arc<Database>) {
         .unwrap();
 
     // Make sure the observer still has a new message
-    let channels_with_new_messages = db
+    let unseen_messages = db
         .transaction(|tx| async move {
-            db.channels_with_new_messages(observer, &[channel_1, channel_2], &*tx)
+            db.unseen_channel_messages(observer, &[channel_1, channel_2], &*tx)
                 .await
         })
         .await
         .unwrap();
     assert_eq!(
-        channels_with_new_messages,
-        [channel_1, channel_2]
-            .into_iter()
-            .collect::<collections::HashSet<_>>()
+        unseen_messages,
+        [
+            rpc::proto::UnseenChannelMessage {
+                channel_id: channel_1.to_proto(),
+                message_id: third_message.to_proto(),
+            },
+            rpc::proto::UnseenChannelMessage {
+                channel_id: channel_2.to_proto(),
+                message_id: fourth_message.to_proto(),
+            },
+        ]
     );
 
     // Observe the third message,
@@ -191,16 +205,20 @@ async fn test_channel_message_new_notification(db: &Arc<Database>) {
         .unwrap();
 
     // Make sure the observer does not have a new method
-    let channels_with_new_messages = db
+    let unseen_messages = db
         .transaction(|tx| async move {
-            db.channels_with_new_messages(observer, &[channel_1, channel_2], &*tx)
+            db.unseen_channel_messages(observer, &[channel_1, channel_2], &*tx)
                 .await
         })
         .await
         .unwrap();
+
     assert_eq!(
-        channels_with_new_messages,
-        [channel_2].into_iter().collect::<collections::HashSet<_>>()
+        unseen_messages,
+        [rpc::proto::UnseenChannelMessage {
+            channel_id: channel_2.to_proto(),
+            message_id: fourth_message.to_proto(),
+        }]
     );
 
     // Observe the second message again, should not regress our observed state
@@ -208,16 +226,19 @@ async fn test_channel_message_new_notification(db: &Arc<Database>) {
         .await
         .unwrap();
 
-    // Make sure the observer does not have a new method
-    let channels_with_new_messages = db
+    // Make sure the observer does not have a new message
+    let unseen_messages = db
         .transaction(|tx| async move {
-            db.channels_with_new_messages(observer, &[channel_1, channel_2], &*tx)
+            db.unseen_channel_messages(observer, &[channel_1, channel_2], &*tx)
                 .await
         })
         .await
         .unwrap();
     assert_eq!(
-        channels_with_new_messages,
-        [channel_2].into_iter().collect::<collections::HashSet<_>>()
+        unseen_messages,
+        [rpc::proto::UnseenChannelMessage {
+            channel_id: channel_2.to_proto(),
+            message_id: fourth_message.to_proto(),
+        }]
     );
 }
diff --git a/crates/collab/src/rpc.rs b/crates/collab/src/rpc.rs
index 371d0466c1..1f0ecce2bf 100644
--- a/crates/collab/src/rpc.rs
+++ b/crates/collab/src/rpc.rs
@@ -274,7 +274,8 @@ impl Server {
             .add_message_handler(unfollow)
             .add_message_handler(update_followers)
             .add_message_handler(update_diff_base)
-            .add_request_handler(get_private_user_info);
+            .add_request_handler(get_private_user_info)
+            .add_message_handler(acknowledge_channel_message);
 
         Arc::new(server)
     }
@@ -2568,16 +2569,8 @@ async fn respond_to_channel_invite(
                         name: channel.name,
                     }),
             );
-        update.notes_changed = result
-            .channels_with_changed_notes
-            .iter()
-            .map(|id| id.to_proto())
-            .collect();
-        update.new_messages = result
-            .channels_with_new_messages
-            .iter()
-            .map(|id| id.to_proto())
-            .collect();
+        update.unseen_channel_messages = result.channel_messages;
+        update.unseen_channel_buffer_changes = result.unseen_buffer_changes;
         update.insert_edge = result.channels.edges;
         update
             .channel_participants
@@ -2701,7 +2694,7 @@ async fn update_channel_buffer(
     let db = session.db().await;
     let channel_id = ChannelId::from_proto(request.channel_id);
 
-    let (collaborators, non_collaborators) = db
+    let (collaborators, non_collaborators, epoch, version) = db
         .update_channel_buffer(channel_id, session.user_id, &request.operations)
         .await?;
 
@@ -2726,7 +2719,11 @@ async fn update_channel_buffer(
             session.peer.send(
                 peer_id.into(),
                 proto::UpdateChannels {
-                    notes_changed: vec![channel_id.to_proto()],
+                    unseen_channel_buffer_changes: vec![proto::UnseenChannelBufferChange {
+                        channel_id: channel_id.to_proto(),
+                        epoch: epoch as u64,
+                        version: version.clone(),
+                    }],
                     ..Default::default()
                 },
             )
@@ -2859,9 +2856,7 @@ async fn send_channel_message(
         message: Some(message),
     })?;
 
-    dbg!(&non_participants);
     let pool = &*session.connection_pool().await;
-
     broadcast(
         None,
         non_participants
@@ -2871,7 +2866,10 @@ async fn send_channel_message(
             session.peer.send(
                 peer_id.into(),
                 proto::UpdateChannels {
-                    new_messages: vec![channel_id.to_proto()],
+                    unseen_channel_messages: vec![proto::UnseenChannelMessage {
+                        channel_id: channel_id.to_proto(),
+                        message_id: message_id.to_proto(),
+                    }],
                     ..Default::default()
                 },
             )
@@ -2900,6 +2898,20 @@ async fn remove_channel_message(
     Ok(())
 }
 
+async fn acknowledge_channel_message(
+    request: proto::AckChannelMessage,
+    session: Session,
+) -> Result<()> {
+    let channel_id = ChannelId::from_proto(request.channel_id);
+    let message_id = MessageId::from_proto(request.message_id);
+    session
+        .db()
+        .await
+        .observe_channel_message(channel_id, session.user_id, message_id)
+        .await?;
+    Ok(())
+}
+
 async fn join_channel_chat(
     request: proto::JoinChannelChat,
     response: Response<proto::JoinChannelChat>,
@@ -3035,18 +3047,8 @@ fn build_initial_channels_update(
         });
     }
 
-    update.notes_changed = channels
-        .channels_with_changed_notes
-        .iter()
-        .map(|channel_id| channel_id.to_proto())
-        .collect();
-
-    update.new_messages = channels
-        .channels_with_new_messages
-        .iter()
-        .map(|channel_id| channel_id.to_proto())
-        .collect();
-
+    update.unseen_channel_buffer_changes = channels.unseen_buffer_changes;
+    update.unseen_channel_messages = channels.channel_messages;
     update.insert_edge = channels.channels.edges;
 
     for (channel_id, participants) in channels.channel_participants {
diff --git a/crates/collab/src/tests/channel_buffer_tests.rs b/crates/collab/src/tests/channel_buffer_tests.rs
index 68acffacf8..d9d12d485b 100644
--- a/crates/collab/src/tests/channel_buffer_tests.rs
+++ b/crates/collab/src/tests/channel_buffer_tests.rs
@@ -445,8 +445,8 @@ fn channel(id: u64, name: &'static str) -> Channel {
     Channel {
         id,
         name: name.to_string(),
-        has_note_changed: false,
-        has_new_messages: false,
+        unseen_note_version: None,
+        unseen_message_id: None,
     }
 }
 
diff --git a/crates/collab/src/tests/test_server.rs b/crates/collab/src/tests/test_server.rs
index a56df311bd..cf5b58703c 100644
--- a/crates/collab/src/tests/test_server.rs
+++ b/crates/collab/src/tests/test_server.rs
@@ -151,12 +151,12 @@ impl TestServer {
 
         Arc::get_mut(&mut client)
             .unwrap()
-            .set_id(user_id.0 as usize)
+            .set_id(user_id.to_proto())
             .override_authenticate(move |cx| {
                 cx.spawn(|_| async move {
                     let access_token = "the-token".to_string();
                     Ok(Credentials {
-                        user_id: user_id.0 as u64,
+                        user_id: user_id.to_proto(),
                         access_token,
                     })
                 })
diff --git a/crates/collab_ui/src/channel_view.rs b/crates/collab_ui/src/channel_view.rs
index 1d9e409748..a955768050 100644
--- a/crates/collab_ui/src/channel_view.rs
+++ b/crates/collab_ui/src/channel_view.rs
@@ -1,6 +1,6 @@
 use anyhow::{anyhow, Result};
 use call::report_call_event_for_channel;
-use channel::{Channel, ChannelBuffer, ChannelBufferEvent, ChannelId};
+use channel::{Channel, ChannelBuffer, ChannelBufferEvent, ChannelId, ChannelStore};
 use client::{
     proto::{self, PeerId},
     Collaborator, ParticipantIndex,
@@ -36,6 +36,7 @@ pub fn init(cx: &mut AppContext) {
 pub struct ChannelView {
     pub editor: ViewHandle<Editor>,
     project: ModelHandle<Project>,
+    channel_store: ModelHandle<ChannelStore>,
     channel_buffer: ModelHandle<ChannelBuffer>,
     remote_id: Option<ViewId>,
     _editor_event_subscription: Subscription,
@@ -94,7 +95,13 @@ impl ChannelView {
             pane.update(&mut cx, |pane, cx| {
                 pane.items_of_type::<Self>()
                     .find(|channel_view| channel_view.read(cx).channel_buffer == channel_buffer)
-                    .unwrap_or_else(|| cx.add_view(|cx| Self::new(project, channel_buffer, cx)))
+                    .unwrap_or_else(|| {
+                        cx.add_view(|cx| {
+                            let mut this = Self::new(project, channel_store, channel_buffer, cx);
+                            this.acknowledge_buffer_version(cx);
+                            this
+                        })
+                    })
             })
             .ok_or_else(|| anyhow!("pane was dropped"))
         })
@@ -102,6 +109,7 @@ impl ChannelView {
 
     pub fn new(
         project: ModelHandle<Project>,
+        channel_store: ModelHandle<ChannelStore>,
         channel_buffer: ModelHandle<ChannelBuffer>,
         cx: &mut ViewContext<Self>,
     ) -> Self {
@@ -121,6 +129,7 @@ impl ChannelView {
         Self {
             editor,
             project,
+            channel_store,
             channel_buffer,
             remote_id: None,
             _editor_event_subscription,
@@ -137,13 +146,44 @@ impl ChannelView {
         event: &ChannelBufferEvent,
         cx: &mut ViewContext<Self>,
     ) {
-        if let ChannelBufferEvent::Disconnected = event {
-            self.editor.update(cx, |editor, cx| {
+        match event {
+            ChannelBufferEvent::Disconnected => self.editor.update(cx, |editor, cx| {
                 editor.set_read_only(true);
                 cx.notify();
-            })
+            }),
+            ChannelBufferEvent::BufferEdited => {
+                if cx.is_self_focused() || self.editor.is_focused(cx) {
+                    self.acknowledge_buffer_version(cx);
+                } else {
+                    self.channel_store.update(cx, |store, cx| {
+                        let channel_buffer = self.channel_buffer.read(cx);
+                        store.notes_changed(
+                            channel_buffer.channel().id,
+                            channel_buffer.epoch(),
+                            &channel_buffer.buffer().read(cx).version(),
+                            cx,
+                        )
+                    });
+                }
+            }
+            _ => {}
         }
     }
+
+    fn acknowledge_buffer_version(&mut self, cx: &mut ViewContext<'_, '_, ChannelView>) {
+        self.channel_store.update(cx, |store, cx| {
+            let channel_buffer = self.channel_buffer.read(cx);
+            store.acknowledge_notes_version(
+                channel_buffer.channel().id,
+                channel_buffer.epoch(),
+                &channel_buffer.buffer().read(cx).version(),
+                cx,
+            )
+        });
+        self.channel_buffer.update(cx, |buffer, cx| {
+            buffer.acknowledge_buffer_version(cx);
+        });
+    }
 }
 
 impl Entity for ChannelView {
@@ -161,6 +201,7 @@ impl View for ChannelView {
 
     fn focus_in(&mut self, _: AnyViewHandle, cx: &mut ViewContext<Self>) {
         if cx.is_self_focused() {
+            self.acknowledge_buffer_version(cx);
             cx.focus(self.editor.as_any())
         }
     }
@@ -200,6 +241,7 @@ impl Item for ChannelView {
     fn clone_on_split(&self, _: WorkspaceId, cx: &mut ViewContext<Self>) -> Option<Self> {
         Some(Self::new(
             self.project.clone(),
+            self.channel_store.clone(),
             self.channel_buffer.clone(),
             cx,
         ))
diff --git a/crates/collab_ui/src/chat_panel.rs b/crates/collab_ui/src/chat_panel.rs
index 81a421e8d9..626b3004d7 100644
--- a/crates/collab_ui/src/chat_panel.rs
+++ b/crates/collab_ui/src/chat_panel.rs
@@ -42,6 +42,7 @@ pub struct ChatPanel {
     local_timezone: UtcOffset,
     fs: Arc<dyn Fs>,
     width: Option<f32>,
+    active: bool,
     pending_serialization: Task<Option<()>>,
     subscriptions: Vec<gpui::Subscription>,
     workspace: WeakViewHandle<Workspace>,
@@ -138,6 +139,7 @@ impl ChatPanel {
                 has_focus: false,
                 subscriptions: Vec::new(),
                 workspace: workspace_handle,
+                active: false,
                 width: None,
             };
 
@@ -154,9 +156,9 @@ impl ChatPanel {
                     }),
                 );
 
-            this.init_active_channel(cx);
+            this.update_channel_count(cx);
             cx.observe(&this.channel_store, |this, _, cx| {
-                this.init_active_channel(cx);
+                this.update_channel_count(cx)
             })
             .detach();
 
@@ -225,10 +227,8 @@ impl ChatPanel {
         );
     }
 
-    fn init_active_channel(&mut self, cx: &mut ViewContext<Self>) {
+    fn update_channel_count(&mut self, cx: &mut ViewContext<Self>) {
         let channel_count = self.channel_store.read(cx).channel_count();
-        self.message_list.reset(0);
-        self.active_chat = None;
         self.channel_select.update(cx, |select, cx| {
             select.set_item_count(channel_count, cx);
         });
@@ -247,6 +247,7 @@ impl ChatPanel {
             }
             let subscription = cx.subscribe(&chat, Self::channel_did_change);
             self.active_chat = Some((chat, subscription));
+            self.acknowledge_last_message(cx);
             self.channel_select.update(cx, |select, cx| {
                 if let Some(ix) = self.channel_store.read(cx).index_of_channel(id) {
                     select.set_selected_index(ix, cx);
@@ -268,11 +269,22 @@ impl ChatPanel {
                 new_count,
             } => {
                 self.message_list.splice(old_range.clone(), *new_count);
+                self.acknowledge_last_message(cx);
             }
         }
         cx.notify();
     }
 
+    fn acknowledge_last_message(&mut self, cx: &mut ViewContext<'_, '_, ChatPanel>) {
+        if self.active {
+            if let Some((chat, _)) = &self.active_chat {
+                chat.update(cx, |chat, cx| {
+                    chat.acknowledge_last_message(cx);
+                });
+            }
+        }
+    }
+
     fn render_channel(&self, cx: &mut ViewContext<Self>) -> AnyElement<Self> {
         let theme = theme::current(cx);
         Flex::column()
@@ -627,8 +639,12 @@ impl Panel for ChatPanel {
     }
 
     fn set_active(&mut self, active: bool, cx: &mut ViewContext<Self>) {
-        if active && !is_chat_feature_enabled(cx) {
-            cx.emit(Event::Dismissed);
+        self.active = active;
+        if active {
+            self.acknowledge_last_message(cx);
+            if !is_chat_feature_enabled(cx) {
+                cx.emit(Event::Dismissed);
+            }
         }
     }
 
diff --git a/crates/collab_ui/src/collab_panel.rs b/crates/collab_ui/src/collab_panel.rs
index 53d5140a12..5e90d438fc 100644
--- a/crates/collab_ui/src/collab_panel.rs
+++ b/crates/collab_ui/src/collab_panel.rs
@@ -1821,7 +1821,7 @@ impl CollabPanel {
                         channel.name.clone(),
                         theme
                             .channel_name
-                            .in_state(channel.has_new_messages)
+                            .in_state(channel.unseen_message_id.is_some())
                             .text
                             .clone(),
                     )
@@ -1880,7 +1880,7 @@ impl CollabPanel {
                         let participants =
                             self.channel_store.read(cx).channel_participants(channel_id);
                         if participants.is_empty() {
-                            if channel.has_note_changed {
+                            if channel.unseen_note_version.is_some() {
                                 Svg::new("icons/terminal.svg")
                                     .with_color(theme.channel_note_active_color)
                                     .constrained()
diff --git a/crates/rpc/proto/zed.proto b/crates/rpc/proto/zed.proto
index 0f289edcf8..3501e70e6a 100644
--- a/crates/rpc/proto/zed.proto
+++ b/crates/rpc/proto/zed.proto
@@ -957,8 +957,19 @@ message UpdateChannels {
     repeated uint64 remove_channel_invitations = 6;
     repeated ChannelParticipants channel_participants = 7;
     repeated ChannelPermission channel_permissions = 8;
-    repeated uint64 notes_changed = 9;
-    repeated uint64 new_messages = 10;
+    repeated UnseenChannelMessage unseen_channel_messages = 9;
+    repeated UnseenChannelBufferChange unseen_channel_buffer_changes = 10;
+}
+
+message UnseenChannelMessage {
+    uint64 channel_id = 1;
+    uint64 message_id = 2;
+}
+
+message UnseenChannelBufferChange {
+    uint64 channel_id = 1;
+    uint64 epoch = 2;
+    repeated VectorClockEntry version = 3;
 }
 
 message ChannelEdge {
@@ -1127,8 +1138,7 @@ message RejoinChannelBuffersResponse {
 message AckBufferOperation {
     uint64 buffer_id = 1;
     uint64 epoch = 2;
-    uint64 lamport_timestamp = 3;
-    uint64 replica_id = 4;
+    repeated VectorClockEntry version = 3;
 }
 
 message JoinChannelBufferResponse {