diff --git a/src/serve_session.rs b/src/serve_session.rs
index cfc6d4f1..05ff0d93 100644
--- a/src/serve_session.rs
+++ b/src/serve_session.rs
@@ -99,6 +99,10 @@ impl<F: ImfsFetcher + Send + 'static> ServeSession<F> {
 }
 
 impl<F: ImfsFetcher> ServeSession<F> {
+    pub fn tree_handle(&self) -> Arc<Mutex<RojoTree>> {
+        Arc::clone(&self.tree)
+    }
+
     pub fn tree(&self) -> MutexGuard<'_, RojoTree> {
         self.tree.lock().unwrap()
     }
diff --git a/src/web/api.rs b/src/web/api.rs
index 1c979e74..8be66359 100644
--- a/src/web/api.rs
+++ b/src/web/api.rs
@@ -13,8 +13,9 @@ use crate::{
     serve_session::ServeSession,
     web::{
         interface::{
-            ErrorResponse, Instance, ReadResponse, ServerInfoResponse, SubscribeMessage,
-            SubscribeResponse, PROTOCOL_VERSION, SERVER_VERSION,
+            ErrorResponse, Instance, InstanceMetadata as WebInstanceMetadata, InstanceUpdate,
+            ReadResponse, ServerInfoResponse, SubscribeMessage, SubscribeResponse,
+            PROTOCOL_VERSION, SERVER_VERSION,
         },
         util::{json, json_ok},
     },
@@ -89,15 +90,46 @@ impl<F: ImfsFetcher> ApiService<F> {
             message_queue.subscribe(input_cursor, sender);
         }
 
+        let tree_handle = self.serve_session.tree_handle();
+
         Box::new(receiver.then(move |result| match result {
             Ok((message_cursor, messages)) => {
-                // TODO: Transform applied patch sets into subscribe responses
+                let tree = tree_handle.lock().unwrap();
+
                 let api_messages = messages
                     .into_iter()
                     .map(|message| {
                         let removed_instances = message.removed;
-                        let added_instances = HashMap::new(); // TODO
-                        let updated_instances = Vec::new(); // TODO
+
+                        let mut added_instances = HashMap::new();
+                        for id in message.added {
+                            let instance = tree.get_instance(id).unwrap();
+                            added_instances.insert(id, Instance::from_rojo_instance(instance));
+
+                            for instance in tree.descendants(id) {
+                                added_instances
+                                    .insert(instance.id(), Instance::from_rojo_instance(instance));
+                            }
+                        }
+
+                        let updated_instances = message
+                            .updated
+                            .into_iter()
+                            .map(|update| {
+                                let changed_metadata = update
+                                    .changed_metadata
+                                    .as_ref()
+                                    .map(WebInstanceMetadata::from_rojo_metadata);
+
+                                InstanceUpdate {
+                                    id: update.id,
+                                    changed_name: update.changed_name,
+                                    changed_class_name: update.changed_class_name,
+                                    changed_properties: update.changed_properties,
+                                    changed_metadata,
+                                }
+                            })
+                            .collect();
 
                         SubscribeMessage {
                             removed_instances,
diff --git a/src/web/interface.rs b/src/web/interface.rs
index a3ab3432..dcfc3bdf 100644
--- a/src/web/interface.rs
+++ b/src/web/interface.rs
@@ -8,7 +8,10 @@ use std::{
 use rbx_dom_weak::{RbxId, RbxValue};
 use serde::{Deserialize, Serialize};
 
-use crate::{session_id::SessionId, snapshot::InstanceWithMeta};
+use crate::{
+    session_id::SessionId,
+    snapshot::{InstanceMetadata as RojoInstanceMetadata, InstanceWithMeta},
+};
 
 /// Server version to report over the API, not exposed outside this crate.
 pub(crate) const SERVER_VERSION: &str = env!("CARGO_PKG_VERSION");
@@ -31,7 +34,9 @@ pub struct InstanceUpdate {
     pub id: RbxId,
     pub changed_name: Option<String>,
     pub changed_class_name: Option<String>,
-    pub changed_properties: HashMap<String, RbxValue>,
+    // TODO: Transform from HashMap<String, Option<_>> to something else, since
+    // null will get lost when decoding from JSON in some languages.
+    pub changed_properties: HashMap<String, Option<RbxValue>>,
     pub changed_metadata: Option<InstanceMetadata>,
 }
 
@@ -41,6 +46,14 @@ pub struct InstanceMetadata {
     pub ignore_unknown_instances: bool,
 }
 
+impl InstanceMetadata {
+    pub(crate) fn from_rojo_metadata(meta: &RojoInstanceMetadata) -> Self {
+        Self {
+            ignore_unknown_instances: meta.ignore_unknown_instances,
+        }
+    }
+}
+
 #[derive(Debug, Serialize, Deserialize)]
 #[serde(rename_all = "PascalCase")]
 pub struct Instance<'a> {
@@ -52,15 +65,13 @@ pub struct Instance<'a> {
 }
 
 impl<'a> Instance<'a> {
-    pub fn from_rojo_instance<'b>(source: InstanceWithMeta<'b>) -> Instance<'b> {
+    pub(crate) fn from_rojo_instance<'b>(source: InstanceWithMeta<'b>) -> Instance<'b> {
         Instance {
             name: Cow::Borrowed(source.name()),
             class_name: Cow::Borrowed(source.class_name()),
             properties: Cow::Borrowed(source.properties()),
             children: Cow::Borrowed(source.children()),
-            metadata: Some(InstanceMetadata {
-                ignore_unknown_instances: source.metadata().ignore_unknown_instances,
-            }),
+            metadata: Some(InstanceMetadata::from_rojo_metadata(source.metadata())),
         }
     }
 }