@@ -114,6 +114,9 @@ export type AuthType = 'signin' | 'signup' | 'recovery';
 /**
  * Get the appropriate FieldType for an input component.
  */
+/** Upper bound on STACK grid slots, so a mistyped `items` cannot render thousands of cells. */
+const MAX_STACK_ITEMS = 12;
+
 const getFieldType = (variant: EmbeddedFlowComponentType): FieldType => {
   switch (variant) {
     case EmbeddedFlowComponentType.EmailInput:
@@ -726,14 +729,48 @@ const createAuthComponentFromFlow = (
       const align: string = (component as any).align || 'center';
       const justify: string = (component as any).justify || 'flex-start';
 
-      const stackStyle: CSSProperties = {
-        alignItems: align,
-        display: 'flex',
-        flexDirection: direction as CSSProperties['flexDirection'],
-        flexWrap: 'wrap',
-        gap: `${gap * 0.5}rem`,
-        justifyContent: justify,
-      };
+      // `items` is the number of slots across the main axis and `direction` picks
+      // that axis: with `row` it is the column count (items: 2 with four buttons
+      // renders a 2 x 2 grid), and with `column` it is the row count and children
+      // flow into further columns. Fewer than two slots keeps the flex layout, so
+      // stacks authored before grid support are unaffected.
+      const rawItems: string | number | undefined = component.items;
+      const parsedItems: number =
+        typeof rawItems === 'string' ? Number(rawItems) : typeof rawItems === 'number' ? rawItems : NaN;
+      const items: number | null =
+        Number.isFinite(parsedItems) && Math.floor(parsedItems) >= 2
+          ? Math.min(Math.floor(parsedItems), MAX_STACK_ITEMS)
+          : null;
+      // CSS Grid has no reverse auto-flow, so the reverse variants fall back to
+      // their base axis rather than silently becoming a row.
+      const isColumn: boolean = direction.startsWith('column');
+      const gridJustify: string = component.justify ?? 'stretch';
+      // Equal `1fr` tracks fill the container, leaving `justify-content` no free
+      // space to distribute. Content-sized tracks restore it, so every justify
+      // value has a visible effect while the default stays an even split.
+      const track: string = gridJustify === 'stretch' ? '1fr' : 'auto';
+
+      const stackStyle: CSSProperties =
+        items !== null
+          ? {
+              alignItems: component.align ?? 'stretch',
+              display: 'grid',
+              gap: `${gap * 0.5}rem`,
+              gridAutoFlow: isColumn ? 'column' : 'row',
+              justifyContent: gridJustify,
+              width: '100%',
+              ...(isColumn
+                ? {gridTemplateRows: `repeat(${items}, ${track})`}
+                : {gridTemplateColumns: `repeat(${items}, ${track})`}),
+            }
+          : {
+              alignItems: align,
+              display: 'flex',
+              flexDirection: direction as CSSProperties['flexDirection'],
+              flexWrap: 'wrap',
+              gap: `${gap * 0.5}rem`,
+              justifyContent: justify,
+            };
 
       const stackChildren: (ReactElement | null)[] = component.components
         ? component.components.map((childComponent: any, index: number) =>
 
@@ -173,3 +173,96 @@ describe('AuthOptionFactory rich-text action', () => {
     expect(() => container.querySelector<HTMLAnchorElement>('a')!.click()).not.toThrow();
   });
 });
+
+describe('AuthOptionFactory stack grid layout', () => {
+  const stackWith = (extra: Record<string, unknown>, childCount = 4): EmbeddedFlowComponent =>
+    ({
+      components: Array.from({length: childCount}, (_, index) => ({
+        id: `text_${index}`,
+        label: `<p>Option ${index}</p>`,
+        type: EmbeddedFlowComponentType.RichText,
+      })),
+      id: 'stack_1',
+      type: EmbeddedFlowComponentType.Stack,
+      ...extra,
+    }) as EmbeddedFlowComponent;
+
+  const stackElement = (component: EmbeddedFlowComponent): HTMLElement => {
+    const {container} = renderInto(component);
+    return container.querySelector<HTMLElement>('#stack_1')!;
+  };
+
+  it('renders a grid with the configured number of columns when items is 2', () => {
+    const stack = stackElement(stackWith({items: 2}));
+
+    expect(stack.style.display).toBe('grid');
+    expect(stack.style.gridTemplateColumns).toBe('repeat(2, 1fr)');
+    expect(stack.children).toHaveLength(4);
+  });
+
+  it('supports arbitrary column counts provided as a numeric string', () => {
+    const stack = stackElement(stackWith({items: '3'}, 5));
+
+    expect(stack.style.display).toBe('grid');
+    expect(stack.style.gridTemplateColumns).toBe('repeat(3, 1fr)');
+    expect(stack.children).toHaveLength(5);
+  });
+
+  it('keeps the flex layout when items is absent', () => {
+    const stack = stackElement(stackWith({direction: 'column'}));
+
+    expect(stack.style.display).toBe('flex');
+    expect(stack.style.flexDirection).toBe('column');
+  });
+
+  it('keeps the flex layout when items is 1', () => {
+    // Stacks authored in the flow builder are seeded with items 1, so a single slot
+    // must not promote them to a grid.
+    const stack = stackElement(stackWith({items: 1}));
+
+    expect(stack.style.display).toBe('flex');
+  });
+
+  it('falls back to the base axis for the reverse directions', () => {
+    expect(stackElement(stackWith({direction: 'column-reverse', items: 2})).style.gridAutoFlow).toBe('column');
+    expect(stackElement(stackWith({direction: 'row-reverse', items: 2})).style.gridAutoFlow).toBe('row');
+  });
+
+  it('uses content-sized tracks when justify has to distribute free space', () => {
+    const stack = stackElement(stackWith({items: 2, justify: 'space-between'}));
+
+    expect(stack.style.gridTemplateColumns).toBe('repeat(2, auto)');
+    expect(stack.style.justifyContent).toBe('space-between');
+  });
+
+  it('keeps equal tracks when justify is unset', () => {
+    expect(stackElement(stackWith({items: 2})).style.gridTemplateColumns).toBe('repeat(2, 1fr)');
+  });
+
+  it('clamps absurd slot counts', () => {
+    const stack = stackElement(stackWith({items: 5000}));
+
+    expect(stack.style.gridTemplateColumns).toBe('repeat(12, 1fr)');
+  });
+
+  it('treats items as the row count when direction is column', () => {
+    const stack = stackElement(stackWith({direction: 'column', items: 2}));
+
+    expect(stack.style.display).toBe('grid');
+    expect(stack.style.gridTemplateRows).toBe('repeat(2, 1fr)');
+    expect(stack.style.gridAutoFlow).toBe('column');
+    expect(stack.style.gridTemplateColumns).toBe('');
+  });
+
+  it('falls back to the flex layout when items is not numeric', () => {
+    const stack = stackElement(stackWith({items: 'garbage'}));
+
+    expect(stack.style.display).toBe('flex');
+  });
+
+  it('falls back to the flex layout when items is a malformed numeric string', () => {
+    const stack = stackElement(stackWith({items: '2invalid'}));
+
+    expect(stack.style.display).toBe('flex');
+  });
+});