diff --git a/ui/src/pages/Inbox.test.tsx b/ui/src/pages/Inbox.test.tsx
index 4a3c61994e6..cc1300d489d 100644
--- a/ui/src/pages/Inbox.test.tsx
+++ b/ui/src/pages/Inbox.test.tsx
@@ -5,7 +5,7 @@ import type { ComponentProps } from "react";
 import { createRoot } from "react-dom/client";
 import type { Issue } from "@paperclipai/shared";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
-import { FailedRunInboxRow, InboxIssueMetaLeading, InboxIssueTrailingColumns } from "./Inbox";
+import { FailedRunInboxRow, InboxGroupHeader, InboxIssueMetaLeading, InboxIssueTrailingColumns } from "./Inbox";
 
 vi.mock("@/lib/router", () => ({
   Link: ({ children, className, ...props }: ComponentProps<"a">) => (
@@ -245,3 +245,52 @@ describe("InboxIssueTrailingColumns", () => {
     });
   });
 });
+
+describe("InboxGroupHeader", () => {
+  let container: HTMLDivElement;
+
+  beforeEach(() => {
+    container = document.createElement("div");
+    document.body.appendChild(container);
+  });
+
+  afterEach(() => {
+    container.remove();
+  });
+
+  it("shows a left caret and expanded state for collapsible mobile headers", () => {
+    const root = createRoot(container);
+
+    act(() => {
+      root.render(<InboxGroupHeader label="Primary workspace (default)" collapsible collapsed={false} />);
+    });
+
+    const button = container.querySelector("button");
+    expect(button).not.toBeNull();
+    expect(button?.getAttribute("aria-expanded")).toBe("true");
+    expect(button?.textContent).toContain("Primary workspace (default)");
+    const caret = container.querySelector("svg");
+    expect(caret?.className.baseVal).toContain("rotate-90");
+
+    act(() => {
+      root.unmount();
+    });
+  });
+
+  it("keeps the caret collapsed when the mobile group is hidden", () => {
+    const root = createRoot(container);
+
+    act(() => {
+      root.render(<InboxGroupHeader label="Feature Branch" collapsible collapsed />);
+    });
+
+    const button = container.querySelector("button");
+    expect(button?.getAttribute("aria-expanded")).toBe("false");
+    const caret = container.querySelector("svg");
+    expect(caret?.className.baseVal).not.toContain("rotate-90");
+
+    act(() => {
+      root.unmount();
+    });
+  });
+});
diff --git a/ui/src/pages/Inbox.tsx b/ui/src/pages/Inbox.tsx
index c438bea1f05..96d53d30312 100644
--- a/ui/src/pages/Inbox.tsx
+++ b/ui/src/pages/Inbox.tsx
@@ -149,6 +149,47 @@ type InboxGroupedSection = {
   isArchivedSearch: boolean;
 };
 
+export function InboxGroupHeader({
+  label,
+  collapsible = false,
+  collapsed = false,
+  onToggle,
+}: {
+  label: string;
+  collapsible?: boolean;
+  collapsed?: boolean;
+  onToggle?: () => void;
+}) {
+  if (collapsible) {
+    return (
+      <button
+        type="button"
+        className="flex w-full items-center gap-2 text-left"
+        aria-expanded={!collapsed}
+        onClick={onToggle}
+      >
+        <ChevronRight
+          className={cn("h-3.5 w-3.5 shrink-0 transition-transform", !collapsed && "rotate-90")}
+        />
+        <span className="max-w-[75vw] truncate rounded-full border border-border/70 bg-background/80 px-2.5 py-0.5 text-[11px] font-medium text-muted-foreground">
+          {label}
+        </span>
+        <span className="h-px flex-1 bg-border/80" />
+      </button>
+    );
+  }
+
+  return (
+    <div className="flex min-w-0 items-center gap-2">
+      <div className="h-px flex-1 bg-border/80" />
+      <span className="max-w-[75vw] truncate rounded-full border border-border/70 bg-background/80 px-2.5 py-0.5 text-[11px] font-medium text-muted-foreground sm:max-w-none">
+        {label}
+      </span>
+      <div className="h-px flex-1 bg-border/80" />
+    </div>
+  );
+}
+
 function buildGroupedInboxSections(
   items: InboxWorkItem[],
   groupBy: InboxWorkItemGroupBy,
@@ -1101,6 +1142,15 @@ export function Inbox() {
     });
   }, []);
   const [collapsedInboxParents, setCollapsedInboxParents] = useState<Set<string>>(new Set());
+  const [collapsedGroupKeys, setCollapsedGroupKeys] = useState<Set<string>>(new Set());
+  const toggleGroupCollapse = useCallback((groupKey: string) => {
+    setCollapsedGroupKeys((prev) => {
+      const next = new Set(prev);
+      if (next.has(groupKey)) next.delete(groupKey);
+      else next.add(groupKey);
+      return next;
+    });
+  }, []);
   const groupedSections = useMemo<InboxGroupedSection[]>(() => [
     ...buildGroupedInboxSections(effectiveWorkItems, groupBy, nestingEnabled, inboxWorkspaceGrouping),
     ...buildGroupedInboxSections(
@@ -2063,6 +2113,8 @@ export function Inbox() {
                 let previousTimestamp = Number.POSITIVE_INFINITY;
                 return groupedSections.flatMap((group, groupIndex) => {
                   const elements: ReactNode[] = [];
+                  const mobileWorkspaceGrouping = isMobile && groupBy === "workspace";
+                  const isGroupCollapsed = mobileWorkspaceGrouping && collapsedGroupKeys.has(group.key);
                   if (group.isArchivedSearch && (groupIndex === 0 || !groupedSections[groupIndex - 1]?.isArchivedSearch)) {
                     elements.push(
                       <div
@@ -2086,16 +2138,16 @@ export function Inbox() {
                           groupIndex > 0 && "border-t border-border",
                         )}
                       >
-                        <div className="flex min-w-0 items-center gap-2">
-                          <div className="h-px flex-1 bg-border/80" />
-                          <span className="max-w-[75vw] truncate rounded-full border border-border/70 bg-background/80 px-2.5 py-0.5 text-[11px] font-medium text-muted-foreground sm:max-w-none">
-                            {group.label}
-                          </span>
-                          <div className="h-px flex-1 bg-border/80" />
-                        </div>
+                        <InboxGroupHeader
+                          label={group.label}
+                          collapsible={mobileWorkspaceGrouping}
+                          collapsed={isGroupCollapsed}
+                          onToggle={mobileWorkspaceGrouping ? () => toggleGroupCollapse(group.key) : undefined}
+                        />
                       </div>,
                     );
                   }
+                  if (isGroupCollapsed) return elements;
 
                   for (let index = 0; index < group.displayItems.length; index += 1) {
                     const item = group.displayItems[index]!;