diff --git a/examples/ai-chatbot/package.json b/examples/ai-chatbot/package.json
index 2d0068d6c..ab21c6912 100644
--- a/examples/ai-chatbot/package.json
+++ b/examples/ai-chatbot/package.json
@@ -18,7 +18,7 @@
     "next": "^16.2.4",
     "react": "^19.2.6",
     "react-dom": "^19.2.6",
-    "stream-chat": "10.0.0-rc.25",
+    "stream-chat": "10.0.0-rc.28",
     "stream-chat-react": "workspace:^"
   },
   "devDependencies": {
diff --git a/examples/cookbook/package.json b/examples/cookbook/package.json
index d49081db7..99518e364 100644
--- a/examples/cookbook/package.json
+++ b/examples/cookbook/package.json
@@ -19,7 +19,7 @@
     "react": "^19.2.6",
     "react-dom": "^19.2.6",
     "react-leaflet": "^5.0.0",
-    "stream-chat": "10.0.0-rc.25",
+    "stream-chat": "10.0.0-rc.28",
     "stream-chat-react": "workspace:^"
   },
   "devDependencies": {
diff --git a/examples/tutorial/package.json b/examples/tutorial/package.json
index c38a10c80..e68162832 100644
--- a/examples/tutorial/package.json
+++ b/examples/tutorial/package.json
@@ -16,7 +16,7 @@
     "emoji-mart": "^5.6.0",
     "react": "^19.2.6",
     "react-dom": "^19.2.6",
-    "stream-chat": "10.0.0-rc.25",
+    "stream-chat": "10.0.0-rc.28",
     "stream-chat-react": "workspace:^"
   },
   "devDependencies": {
diff --git a/examples/vite/package.json b/examples/vite/package.json
index 7148ee8e1..3a10f9874 100644
--- a/examples/vite/package.json
+++ b/examples/vite/package.json
@@ -18,7 +18,7 @@
     "modern-normalize": "^3.0.1",
     "react": "^19.2.6",
     "react-dom": "^19.2.6",
-    "stream-chat": "10.0.0-rc.25",
+    "stream-chat": "10.0.0-rc.28",
     "stream-chat-react": "workspace:^"
   },
   "devDependencies": {
diff --git a/package.json b/package.json
index 0bce69b73..8b4b45972 100644
--- a/package.json
+++ b/package.json
@@ -144,7 +144,7 @@
     "modern-normalize": "^3.0.1",
     "react": "^19.0.0 || ^18.0.0 || ^17.0.0",
     "react-dom": "^19.0.0 || ^18.0.0 || ^17.0.0",
-    "stream-chat": "^10.0.0-rc.25"
+    "stream-chat": "^10.0.0-rc.28"
   },
   "peerDependenciesMeta": {
     "@breezystack/lamejs": {
@@ -210,7 +210,7 @@
     "react-dom": "^19.2.6",
     "sass": "^1.100.0",
     "semantic-release": "^25.0.3",
-    "stream-chat": "10.0.0-rc.25",
+    "stream-chat": "10.0.0-rc.28",
     "typescript": "^6.0.3",
     "typescript-eslint": "^8.59.4",
     "vite": "^8.1.3",
diff --git a/src/components/MessageComposer/__tests__/MessageInput.test.tsx b/src/components/MessageComposer/__tests__/MessageInput.test.tsx
index 4a9402231..fc1119762 100644
--- a/src/components/MessageComposer/__tests__/MessageInput.test.tsx
+++ b/src/components/MessageComposer/__tests__/MessageInput.test.tsx
@@ -1075,7 +1075,7 @@ describe(`MessageInputFlat`, () => {
       await waitFor(() => {
         expect(sendMessageMock).toHaveBeenCalledWith(
           customChannel,
-          expect.objectContaining(customMessageData),
+          expect.objectContaining({ custom: customMessageData }),
           {},
         );
       });
@@ -1103,11 +1103,12 @@ describe(`MessageInputFlat`, () => {
 
       await act(() => submit());
 
-      // The custom handler receives the composed message (text + custom data) and the send options.
+      // The custom handler receives the composed message (text + custom data, nested under `custom`)
+      // and the send options.
       await waitFor(() =>
         expect(sendMessageMock).toHaveBeenCalledWith(
           customChannel,
-          expect.objectContaining({ text: messageText, ...customMessageData }),
+          expect.objectContaining({ custom: customMessageData, text: messageText }),
           {},
         ),
       );
diff --git a/src/mock-builders/event/messageDelivered.ts b/src/mock-builders/event/messageDelivered.ts
index 40b45693d..3ae9c210c 100644
--- a/src/mock-builders/event/messageDelivered.ts
+++ b/src/mock-builders/event/messageDelivered.ts
@@ -15,11 +15,9 @@ type MessageDeliveredEvent = {
   channel_member_count: number;
   channel_type: string;
   cid: string;
-  // `created_at` is unix nanoseconds like other wire timestamps, but the spec declares
-  // `last_delivered_at` as a plain string, so it arrives as RFC3339.
   created_at: TimestampNS;
   custom: CustomEventData;
-  last_delivered_at: string;
+  last_delivered_at: TimestampNS;
   last_delivered_message_id: string;
   user: UserResponse;
 };
@@ -35,7 +33,7 @@ export const makeMessageDeliveredEvent = (
   cid: 'messaging:test',
   created_at: convertDateToTimestamp('2025-09-16T13:25:57.996011272Z'),
   custom: {},
-  last_delivered_at: '2025-09-16T13:25:57Z',
+  last_delivered_at: convertDateToTimestamp('2025-09-16T13:25:57Z'),
   last_delivered_message_id: 'aefbf38a-0e02-4ba6-a480-e595c37ec78a',
   type: 'message.delivered',
   user: {
@@ -74,7 +72,7 @@ export const dispatchMessageDeliveredEvent = ({
       channel_type: channel.type,
       cid: channel.cid,
       created_at: convertDateToTimestamp(),
-      last_delivered_at: deliveredAt,
+      last_delivered_at: convertDateToTimestamp(deliveredAt),
       last_delivered_message_id: lastDeliveredMessageId,
       user,
     }),
diff --git a/yarn.lock b/yarn.lock
index 56c831af2..d2028223e 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2160,14 +2160,14 @@ __metadata:
   languageName: node
   linkType: hard
 
-"@stream-io/logger@npm:^2.0.0":
+"@stream-io/logger@npm:^2.1.0":
   version: 2.1.0
   resolution: "@stream-io/logger@npm:2.1.0"
   checksum: 10c0/0a09c9420b8bbec7a3007bf02acccaf7c0792b18d76eb791198e2a20890f1244b42788c3cc99d6ab52a591f49fde80dd6b2236e194f95f03b36fce5d0aa71dc3
   languageName: node
   linkType: hard
 
-"@stream-io/state-store@npm:^1.1.6, @stream-io/state-store@npm:^1.2.0":
+"@stream-io/state-store@npm:^1.2.0":
   version: 1.2.0
   resolution: "@stream-io/state-store@npm:1.2.0"
   peerDependencies:
@@ -2197,7 +2197,7 @@ __metadata:
     react: "npm:^19.2.6"
     react-dom: "npm:^19.2.6"
     sass: "npm:^1.100.0"
-    stream-chat: "npm:10.0.0-rc.25"
+    stream-chat: "npm:10.0.0-rc.28"
     stream-chat-react: "workspace:^"
     typescript: "npm:^6.0.3"
   languageName: unknown
@@ -2219,7 +2219,7 @@ __metadata:
     react: "npm:^19.2.6"
     react-dom: "npm:^19.2.6"
     react-leaflet: "npm:^5.0.0"
-    stream-chat: "npm:10.0.0-rc.25"
+    stream-chat: "npm:10.0.0-rc.28"
     stream-chat-react: "workspace:^"
     typescript: "npm:^6.0.3"
     vite: "npm:^8.1.3"
@@ -2237,7 +2237,7 @@ __metadata:
     emoji-mart: "npm:^5.6.0"
     react: "npm:^19.2.6"
     react-dom: "npm:^19.2.6"
-    stream-chat: "npm:10.0.0-rc.25"
+    stream-chat: "npm:10.0.0-rc.28"
     stream-chat-react: "workspace:^"
     typescript: "npm:^6.0.3"
     vite: "npm:^8.1.3"
@@ -2265,7 +2265,7 @@ __metadata:
     react: "npm:^19.2.6"
     react-dom: "npm:^19.2.6"
     sass: "npm:^1.100.0"
-    stream-chat: "npm:10.0.0-rc.25"
+    stream-chat: "npm:10.0.0-rc.28"
     stream-chat-react: "workspace:^"
     typescript: "npm:^6.0.3"
     vite: "npm:^8.1.3"
@@ -10340,7 +10340,7 @@ __metadata:
     remark-parse: "npm:^11.0.0"
     sass: "npm:^1.100.0"
     semantic-release: "npm:^25.0.3"
-    stream-chat: "npm:10.0.0-rc.25"
+    stream-chat: "npm:10.0.0-rc.28"
     typescript: "npm:^6.0.3"
     typescript-eslint: "npm:^8.59.4"
     unified: "npm:^11.0.5"
@@ -10358,7 +10358,7 @@ __metadata:
     modern-normalize: ^3.0.1
     react: ^19.0.0 || ^18.0.0 || ^17.0.0
     react-dom: ^19.0.0 || ^18.0.0 || ^17.0.0
-    stream-chat: ^10.0.0-rc.25
+    stream-chat: ^10.0.0-rc.28
   dependenciesMeta:
     "@parcel/watcher":
       built: true
@@ -10382,12 +10382,12 @@ __metadata:
   languageName: unknown
   linkType: soft
 
-"stream-chat@npm:10.0.0-rc.25":
-  version: 10.0.0-rc.25
-  resolution: "stream-chat@npm:10.0.0-rc.25"
+"stream-chat@npm:10.0.0-rc.28":
+  version: 10.0.0-rc.28
+  resolution: "stream-chat@npm:10.0.0-rc.28"
   dependencies:
-    "@stream-io/logger": "npm:^2.0.0"
-    "@stream-io/state-store": "npm:^1.1.6"
+    "@stream-io/logger": "npm:^2.1.0"
+    "@stream-io/state-store": "npm:^1.2.0"
     axios: "npm:^1.19.0"
     linkifyjs: "npm:^4.3.3"
   dependenciesMeta:
@@ -10395,7 +10395,7 @@ __metadata:
       built: true
     husky:
       built: true
-  checksum: 10c0/cb8a316988d73c00347c9a98047246ac05cbedcba28560afaa6358b6e022b84350a51bb80a73bf3376ff68a91fffe2d203414831b342200cde831972ea027d11
+  checksum: 10c0/0132ae268d1b228eeb8b70a08b03eff77e955f8a2215fcf7804fa4df8dd7c032adc3a356d934cbf883fd4835f823612ec9d53ccf3948c494023ae5d636341f01
   languageName: node
   linkType: hard