diff --git a/src/elements/content-sidebar/activity-feed-v2/ActivityFeedV2.tsx b/src/elements/content-sidebar/activity-feed-v2/ActivityFeedV2.tsx
index 84ee811a76..39dd23ae03 100644
--- a/src/elements/content-sidebar/activity-feed-v2/ActivityFeedV2.tsx
+++ b/src/elements/content-sidebar/activity-feed-v2/ActivityFeedV2.tsx
@@ -18,7 +18,7 @@ import TaskModalV2 from './task-modal-v2';
 import FeedItemRow from './FeedItemRow';
 import { serializeEditorContent } from './helpers';
 import { mapCollaboratorToUserContact } from './task-modal-v2/utils/contactMapping';
-import { transformFeedItem } from './transformers';
+import { transformFeedItem, transformTaskAssignees } from './transformers';
 import { useAvatarUrls } from './useAvatarUrls';
 import { useTimeFormat } from './useTimeFormat';
 import { useVideoTimestamp } from './useVideoTimestamp';
@@ -230,6 +230,24 @@ const ActivityFeedV2 = ({
 
     const avatarUrls = useAvatarUrls(feedItems, getAvatarUrl);
 
+    // Loads the full assignee list (limit=API_PAGE_LIMIT via getTaskCollaborators) when the
+    // assignee list's "Show more" is clicked on a task whose embedded first page of assignees
+    // was incomplete (assigned_to.next_marker present, i.e. hasNextPage). Rejections are
+    // rethrown so AssigneeList can render its inline load error.
+    const handleTaskLoadAllAssignees = React.useMemo(() => {
+        if (!getTaskCollaborators) return undefined;
+        return async (task: TaskNew) => {
+            try {
+                const collection = await getTaskCollaborators(task);
+                return transformTaskAssignees(collection.entries, avatarUrls);
+            } catch (error) {
+                // eslint-disable-next-line no-console
+                console.error(`ActivityFeedV2: failed to load assignees for task "${task.id}"`, error);
+                throw error;
+            }
+        };
+    }, [avatarUrls, getTaskCollaborators]);
+
     const transformedItems: TransformedFeedItem[] = React.useMemo(() => {
         if (!feedItems) return [];
         return feedItems.reduce<TransformedFeedItem[]>((acc, item) => {
@@ -507,6 +525,7 @@ const ActivityFeedV2 = ({
                                     onTaskAssignmentUpdate={onTaskAssignmentUpdate}
                                     onTaskDelete={onTaskDelete}
                                     onTaskEdit={onTaskUpdate ? handleTaskEdit : undefined}
+                                    onTaskLoadAllAssignees={handleTaskLoadAllAssignees}
                                     onTaskView={onTaskView}
                                     onVersionHistoryClick={onVersionHistoryClick}
                                     timeFormat={timeFormat}
diff --git a/src/elements/content-sidebar/activity-feed-v2/FeedItemRow.tsx b/src/elements/content-sidebar/activity-feed-v2/FeedItemRow.tsx
index 311a08b7e9..5a6682615f 100644
--- a/src/elements/content-sidebar/activity-feed-v2/FeedItemRow.tsx
+++ b/src/elements/content-sidebar/activity-feed-v2/FeedItemRow.tsx
@@ -18,7 +18,7 @@ import { annotationTargetToBadge } from './transformers';
 import { formatByTimeFormat } from './useTimeFormat';
 import { seekVideoToMs } from './useVideoTimestamp';
 
-import type { OnReplyDelete, OnReplyUpdate, TransformedFeedItem, UserSelectorProps } from './types';
+import type { OnReplyDelete, OnReplyUpdate, TaskItemProps, TransformedFeedItem, UserSelectorProps } from './types';
 
 import {
     FEED_ITEM_TYPE_ANNOTATION,
@@ -61,6 +61,7 @@ type FeedItemRowProps = {
     onTaskAssignmentUpdate?: (taskId: string, taskAssignmentId: string, status: TaskCollabStatus) => void;
     onTaskDelete?: (task: TaskNew) => void;
     onTaskEdit?: (task: TaskNew) => void;
+    onTaskLoadAllAssignees?: (task: TaskNew) => Promise<TaskItemProps['assignees']>;
     onTaskView?: (id: string, isCreator: boolean) => void;
     onVersionHistoryClick?: (version: { id: string; version_number: number }) => void;
     timeFormat: TimeFormat;
@@ -101,6 +102,7 @@ const FeedItemRow = ({
     onTaskAssignmentUpdate,
     onTaskDelete,
     onTaskEdit,
+    onTaskLoadAllAssignees,
     onTaskView,
     onVersionHistoryClick,
     timeFormat,
@@ -269,6 +271,9 @@ const FeedItemRow = ({
                     onComplete={canActOnAssignment ? () => handleAssignmentUpdate(TASK_NEW_COMPLETED) : undefined}
                     onDelete={onTaskDelete ? () => onTaskDelete(item.originalTask) : undefined}
                     onEdit={onTaskEdit ? () => onTaskEdit(item.originalTask) : undefined}
+                    onLoadAllAssignee={
+                        onTaskLoadAllAssignees ? () => onTaskLoadAllAssignees(item.originalTask) : undefined
+                    }
                     onReject={canActOnAssignment ? () => handleAssignmentUpdate(TASK_NEW_REJECTED) : undefined}
                     onView={
                         onTaskView
diff --git a/src/elements/content-sidebar/activity-feed-v2/__tests__/ActivityFeedV2.test.tsx b/src/elements/content-sidebar/activity-feed-v2/__tests__/ActivityFeedV2.test.tsx
index 9d5c83086e..003c1a1cb0 100644
--- a/src/elements/content-sidebar/activity-feed-v2/__tests__/ActivityFeedV2.test.tsx
+++ b/src/elements/content-sidebar/activity-feed-v2/__tests__/ActivityFeedV2.test.tsx
@@ -28,12 +28,18 @@ const mockScrollTo = jest.fn<boolean, [string]>(() => true);
 type FilterMenuProps = { children?: React.ReactNode; hasActiveFilters?: boolean };
 type FilterOptionProps = { checked?: boolean; onCheckedChange?: (checked: boolean) => void };
 type RootProps = React.ComponentProps<typeof ActivityFeed.Root>;
+type TaskListItemProps = {
+    hasNextPage?: boolean;
+    id: string;
+    onLoadAllAssignee?: () => Promise<unknown>;
+};
 let lastFilterMenuProps: FilterMenuProps = {};
 let lastShowResolvedOptionProps: FilterOptionProps = {};
 let lastMentionMeOptionProps: FilterOptionProps = {};
 let lastEditorProps: Partial<EditorProps> = {};
 let lastRootProps: Partial<RootProps> = {};
 let lastTaskModalProps: Partial<TaskModalV2Props> = {};
+let lastTaskItemProps: Partial<TaskListItemProps> = {};
 
 jest.mock('../task-modal-v2', () => ({
     __esModule: true,
@@ -55,7 +61,10 @@ jest.mock('@box/activity-feed', () => {
     ActivityFeedList.AppActivity = (props: { id: string }) => (
         <div data-testid={`app-activity-${props.id}`}>AppActivity</div>
     );
-    ActivityFeedList.Task = (props: { id: string }) => <div data-testid={`task-${props.id}`}>Task</div>;
+    ActivityFeedList.Task = (props: TaskListItemProps) => {
+        lastTaskItemProps = props;
+        return <div data-testid={`task-${props.id}`}>Task</div>;
+    };
     ActivityFeedList.ThreadedAnnotation = (props: { messages?: Array<{ id: string }> }) => (
         <div data-testid={`threaded-annotation-${props.messages?.[0]?.id}`}>ThreadedAnnotation</div>
     );
@@ -186,6 +195,7 @@ describe('elements/content-sidebar/activity-feed-v2/ActivityFeedV2', () => {
         lastEditorProps = {};
         lastRootProps = {};
         lastTaskModalProps = {};
+        lastTaskItemProps = {};
         mockSerializeMentionMarkup.mockImplementation((doc: unknown) => ({
             hasMention: false,
             text: JSON.stringify(doc),
@@ -252,6 +262,109 @@ describe('elements/content-sidebar/activity-feed-v2/ActivityFeedV2', () => {
         expect(screen.getByTestId('task-task-1')).toBeVisible();
     });
 
+    describe('task assignee loading', () => {
+        // First page of assignees is partial (next_marker set), so hasNextPage is passed as true
+        // to the Task item (which is what makes the real AssigneeList offer "Show more")
+        const taskWithMoreAssignees = {
+            ...mockTask,
+            assigned_to: {
+                entries: [
+                    {
+                        id: 'assignment-1',
+                        permissions: { can_delete: true, can_update: true },
+                        role: 'ASSIGNEE',
+                        status: 'NOT_STARTED',
+                        target: { id: 'user-2', name: 'Assignee One', type: 'user' },
+                        type: 'task_collaborator',
+                    },
+                ],
+                limit: 20,
+                next_marker: 'marker-1',
+            },
+        };
+
+        test('should fetch and transform the full assignee list when onLoadAllAssignee fires', async () => {
+            const getTaskCollaborators = jest.fn().mockResolvedValue({
+                entries: [
+                    {
+                        id: 'assignment-1',
+                        permissions: { can_delete: true, can_update: true },
+                        role: 'ASSIGNEE',
+                        status: 'NOT_STARTED',
+                        target: { id: 'user-2', name: 'Assignee One', type: 'user' },
+                        type: 'task_collaborator',
+                    },
+                    {
+                        completed_at: '2024-03-02T00:00:00Z',
+                        id: 'assignment-2',
+                        permissions: { can_delete: false, can_update: false },
+                        role: 'ASSIGNEE',
+                        status: 'COMPLETED',
+                        target: { id: 'user-3', name: 'Assignee Two', type: 'user' },
+                        type: 'task_collaborator',
+                    },
+                ],
+                limit: 1000,
+                next_marker: null,
+            });
+            render(
+                <ActivityFeedV2
+                    currentUser={mockCurrentUser}
+                    feedItems={[taskWithMoreAssignees] as ActivityFeedV2Props['feedItems']}
+                    getTaskCollaborators={getTaskCollaborators}
+                />,
+            );
+
+            expect(lastTaskItemProps.hasNextPage).toBe(true);
+
+            const result = await lastTaskItemProps.onLoadAllAssignee?.();
+
+            expect(getTaskCollaborators).toHaveBeenCalledWith(taskWithMoreAssignees);
+            expect(result).toEqual([
+                expect.objectContaining({ id: 'user-2', name: 'Assignee One', status: 'NOT_STARTED' }),
+                expect.objectContaining({
+                    completedAt: new Date('2024-03-02T00:00:00Z').getTime(),
+                    id: 'user-3',
+                    name: 'Assignee Two',
+                    status: 'COMPLETED',
+                }),
+            ]);
+        });
+
+        test('should omit onLoadAllAssignee when getTaskCollaborators is not provided', () => {
+            render(
+                <ActivityFeedV2
+                    currentUser={mockCurrentUser}
+                    feedItems={[taskWithMoreAssignees] as ActivityFeedV2Props['feedItems']}
+                />,
+            );
+
+            expect(lastTaskItemProps.hasNextPage).toBe(true);
+            expect(lastTaskItemProps.onLoadAllAssignee).toBeUndefined();
+        });
+
+        test('should log and rethrow when getTaskCollaborators rejects so AssigneeList can show its error state', async () => {
+            const loadError = new Error('network failure');
+            const getTaskCollaborators = jest.fn().mockRejectedValue(loadError);
+            const consoleSpy = jest.spyOn(console, 'error').mockImplementation(() => undefined);
+            render(
+                <ActivityFeedV2
+                    currentUser={mockCurrentUser}
+                    feedItems={[taskWithMoreAssignees] as ActivityFeedV2Props['feedItems']}
+                    getTaskCollaborators={getTaskCollaborators}
+                />,
+            );
+
+            await expect(lastTaskItemProps.onLoadAllAssignee?.()).rejects.toThrow('network failure');
+
+            expect(consoleSpy).toHaveBeenCalledWith(
+                'ActivityFeedV2: failed to load assignees for task "task-1"',
+                loadError,
+            );
+            consoleSpy.mockRestore();
+        });
+    });
+
     test('should render version feed items alongside other items', () => {
         render(
             <ActivityFeedV2
diff --git a/src/elements/content-sidebar/activity-feed-v2/__tests__/FeedItemRow.test.tsx b/src/elements/content-sidebar/activity-feed-v2/__tests__/FeedItemRow.test.tsx
index 8ce4274b93..81b365ccfd 100644
--- a/src/elements/content-sidebar/activity-feed-v2/__tests__/FeedItemRow.test.tsx
+++ b/src/elements/content-sidebar/activity-feed-v2/__tests__/FeedItemRow.test.tsx
@@ -882,6 +882,23 @@ describe('elements/content-sidebar/activity-feed-v2/FeedItemRow', () => {
 
             expect(lastTaskProps.onEdit).toBeUndefined();
         });
+
+        test('should call onTaskLoadAllAssignees with the original task when onLoadAllAssignee fires', async () => {
+            const allAssignees = [{ id: 'user-1', name: 'Creator', status: 'NOT_STARTED' }];
+            const onTaskLoadAllAssignees = jest.fn().mockResolvedValue(allAssignees);
+            render(<FeedItemRow {...defaultProps} item={mockTask} onTaskLoadAllAssignees={onTaskLoadAllAssignees} />);
+
+            const result = await lastTaskProps.onLoadAllAssignee?.();
+
+            expect(onTaskLoadAllAssignees).toHaveBeenCalledWith(mockOriginalTask);
+            expect(result).toEqual(allAssignees);
+        });
+
+        test('should omit onLoadAllAssignee when onTaskLoadAllAssignees is not provided', () => {
+            render(<FeedItemRow {...defaultProps} item={mockTask} />);
+
+            expect(lastTaskProps.onLoadAllAssignee).toBeUndefined();
+        });
     });
 
     describe('version rendering', () => {
diff --git a/src/elements/content-sidebar/activity-feed-v2/transformers.ts b/src/elements/content-sidebar/activity-feed-v2/transformers.ts
index bb511a9cba..2ab8006bdc 100644
--- a/src/elements/content-sidebar/activity-feed-v2/transformers.ts
+++ b/src/elements/content-sidebar/activity-feed-v2/transformers.ts
@@ -23,7 +23,7 @@ import { convertMillisecondsToTimestamp } from '../../../utils/timestamp';
 import type { Annotation, Target } from '../../../common/types/annotations';
 import type { AppActivityItem as BUIEAppActivityItem, Comment, FeedItem } from '../../../common/types/feed';
 import type { BoxItemVersion, User } from '../../../common/types/core';
-import type { TaskNew } from '../../../common/types/tasks';
+import type { TaskCollabAssignee, TaskNew } from '../../../common/types/tasks';
 
 import type {
     AnnotationBadgeTargetType,
@@ -230,12 +230,11 @@ export const transformAnnotationToMessages = (annotation: Annotation, avatarUrls
     return [root, ...replies];
 };
 
-export const transformTaskToProps = (
-    task: TaskNew,
-    currentUserId?: string,
+export const transformTaskAssignees = (
+    entries: TaskCollabAssignee[],
     avatarUrls?: AvatarUrlMap,
-): TaskItemProps => ({
-    assignees: (task.assigned_to?.entries ?? []).map(entry => ({
+): TaskItemProps['assignees'] =>
+    entries.map(entry => ({
         avatarUrl: resolveAvatarUrl(entry.target?.id, avatarUrls),
         completedAt: toUnixMs(entry.completed_at),
         id: entry.target?.id ?? entry.id,
@@ -244,7 +243,14 @@ export const transformTaskToProps = (
             ? { canDelete: entry.permissions.can_delete, canUpdate: entry.permissions.can_update }
             : undefined,
         status: entry.status as TaskItemProps['assignees'][number]['status'],
-    })),
+    }));
+
+export const transformTaskToProps = (
+    task: TaskNew,
+    currentUserId?: string,
+    avatarUrls?: AvatarUrlMap,
+): TaskItemProps => ({
+    assignees: transformTaskAssignees(task.assigned_to?.entries ?? [], avatarUrls),
     author: {
         avatarUrl: resolveAvatarUrl(task.created_by?.target?.id, avatarUrls),
         id: task.created_by?.target?.id ?? '',