diff --git a/apps/web/src/components/DiffPanel.tsx b/apps/web/src/components/DiffPanel.tsx
index 04d86f81eeb..3a30fbb2c7e 100644
--- a/apps/web/src/components/DiffPanel.tsx
+++ b/apps/web/src/components/DiffPanel.tsx
@@ -11,6 +11,8 @@ import {
   CheckIcon,
   ChevronDownIcon,
   ChevronRightIcon,
+  ChevronsDownUpIcon,
+  ChevronsUpDownIcon,
   Columns2Icon,
   PilcrowIcon,
   Rows3Icon,
@@ -32,6 +34,7 @@ import {
   resolveDiffThemeName,
   resolveFileDiffPath,
 } from "../lib/diffRendering";
+import { areAllDiffFilesCollapsed, toggleAllDiffFiles } from "../lib/diffCollapse";
 import { useTurnDiffSummaries } from "../hooks/useTurnDiffSummaries";
 import { useProject, useThread } from "../state/entities";
 import { resolveThreadRouteRef } from "../threadRoutes";
@@ -39,6 +42,7 @@ import { useClientSettings } from "../hooks/useSettings";
 import { formatShortTimestamp } from "../timestampFormat";
 import { DiffPanelLoadingState, DiffPanelShell, type DiffPanelMode } from "./DiffPanelShell";
 import { AnnotatableCodeView, type AnnotatableCodeViewHandle } from "./diffs/AnnotatableCodeView";
+import { Button } from "./ui/button";
 import { ToggleGroup, Toggle } from "./ui/toggle-group";
 import { Switch } from "./ui/switch";
 import {
@@ -446,6 +450,8 @@ export default function DiffPanel({
       }),
     [collapsedDiffFileKeys, renderableFiles],
   );
+  const diffFileKeys = useMemo(() => codeViewFiles.map((file) => file.fileKey), [codeViewFiles]);
+  const allDiffFilesCollapsed = areAllDiffFilesCollapsed(diffFileKeys, collapsedDiffFileKeys);
 
   useEffect(() => {
     if (!selectedFilePath) return;
@@ -496,6 +502,18 @@ export default function DiffPanel({
     [collapseScopeKey],
   );
 
+  const toggleDiffFileCollapse = useCallback(() => {
+    setCollapsedDiffFiles((current) => {
+      const currentKeys =
+        current.scopeKey === collapseScopeKey ? current.fileKeys : EMPTY_COLLAPSED_DIFF_FILE_KEYS;
+
+      return {
+        scopeKey: collapseScopeKey,
+        fileKeys: toggleAllDiffFiles(diffFileKeys, currentKeys),
+      };
+    });
+  }, [collapseScopeKey, diffFileKeys]);
+
   const selectTurn = (turnId: TurnId) => {
     if (!routeThreadRef) return;
     useDiffPanelStore.getState().selectTurn(routeThreadRef, turnId);
@@ -695,6 +713,30 @@ export default function DiffPanel({
         )}
       </div>
       <div className="flex shrink-0 items-center gap-1 [-webkit-app-region:no-drag]">
+        {codeViewFiles.length > 0 && (
+          <Tooltip>
+            <TooltipTrigger
+              render={
+                <Button
+                  type="button"
+                  size="icon-xs"
+                  variant="outline"
+                  aria-label={allDiffFilesCollapsed ? "Expand all files" : "Collapse all files"}
+                  onClick={toggleDiffFileCollapse}
+                />
+              }
+            >
+              {allDiffFilesCollapsed ? (
+                <ChevronsUpDownIcon className="size-3" />
+              ) : (
+                <ChevronsDownUpIcon className="size-3" />
+              )}
+            </TooltipTrigger>
+            <TooltipPopup side="top">
+              {allDiffFilesCollapsed ? "Expand all files" : "Collapse all files"}
+            </TooltipPopup>
+          </Tooltip>
+        )}
         <ToggleGroup
           className="shrink-0"
           variant="outline"
@@ -824,7 +866,7 @@ export default function DiffPanel({
                 <AnnotatableCodeView
                   viewerRef={codeViewRef}
                   key={collapseScopeKey ?? reviewSectionId}
-                  className="diff-render-surface h-full min-h-0 overflow-auto"
+                  className="diff-render-surface h-full min-h-0 overflow-auto [&>div>div:last-child]:top-0! [&>div>div:last-child]:bottom-auto!"
                   files={codeViewFiles}
                   sectionId={reviewSectionId}
                   sectionTitle={reviewSectionTitle}
diff --git a/apps/web/src/lib/diffCollapse.test.ts b/apps/web/src/lib/diffCollapse.test.ts
new file mode 100644
index 00000000000..d46f6ec963e
--- /dev/null
+++ b/apps/web/src/lib/diffCollapse.test.ts
@@ -0,0 +1,22 @@
+import { describe, expect, it } from "vite-plus/test";
+
+import { areAllDiffFilesCollapsed, toggleAllDiffFiles } from "./diffCollapse";
+
+const FILE_KEYS = ["src/app.ts", "src/index.ts"];
+const FIRST_FILE_KEY = FILE_KEYS[0]!;
+
+describe("diff collapse controls", () => {
+  it("reports whether every rendered file is collapsed", () => {
+    expect(areAllDiffFilesCollapsed(FILE_KEYS, new Set(FILE_KEYS))).toBe(true);
+    expect(areAllDiffFilesCollapsed(FILE_KEYS, new Set([FIRST_FILE_KEY]))).toBe(false);
+    expect(areAllDiffFilesCollapsed([], new Set())).toBe(false);
+  });
+
+  it("collapses all files when any rendered file is expanded", () => {
+    expect(toggleAllDiffFiles(FILE_KEYS, new Set([FIRST_FILE_KEY]))).toEqual(new Set(FILE_KEYS));
+  });
+
+  it("expands all files when every rendered file is collapsed", () => {
+    expect(toggleAllDiffFiles(FILE_KEYS, new Set(FILE_KEYS))).toEqual(new Set());
+  });
+});
diff --git a/apps/web/src/lib/diffCollapse.ts b/apps/web/src/lib/diffCollapse.ts
new file mode 100644
index 00000000000..51bdcaf94ac
--- /dev/null
+++ b/apps/web/src/lib/diffCollapse.ts
@@ -0,0 +1,13 @@
+export function areAllDiffFilesCollapsed(
+  fileKeys: ReadonlyArray<string>,
+  collapsedFileKeys: ReadonlySet<string>,
+): boolean {
+  return fileKeys.length > 0 && fileKeys.every((fileKey) => collapsedFileKeys.has(fileKey));
+}
+
+export function toggleAllDiffFiles(
+  fileKeys: ReadonlyArray<string>,
+  collapsedFileKeys: ReadonlySet<string>,
+): ReadonlySet<string> {
+  return areAllDiffFilesCollapsed(fileKeys, collapsedFileKeys) ? new Set() : new Set(fileKeys);
+}