diff --git a/.changeset/responsive-anchored-overlay.md b/.changeset/responsive-anchored-overlay.md
new file mode 100644
index 00000000000..dd3590df18b
--- /dev/null
+++ b/.changeset/responsive-anchored-overlay.md
@@ -0,0 +1,5 @@
+---
+"@primer/react": minor
+---
+
+AnchoredOverlay: Add prop to set responsive variant. Example: `variant: {regular: 'anchored', narrow: 'anchored'}`
diff --git a/.playwright/snapshots/components/SelectPanel.test.ts-snapshots/SelectPanel-Default-responsive-width-light-modern-action-list--true-linux.png b/.playwright/snapshots/components/SelectPanel.test.ts-snapshots/SelectPanel-Default-responsive-width-light-modern-action-list--true-linux.png
new file mode 100644
index 00000000000..1b994c3baf1
Binary files /dev/null and b/.playwright/snapshots/components/SelectPanel.test.ts-snapshots/SelectPanel-Default-responsive-width-light-modern-action-list--true-linux.png differ
diff --git a/e2e/components/SelectPanel.test.ts b/e2e/components/SelectPanel.test.ts
index 09904ec1816..49198328841 100644
--- a/e2e/components/SelectPanel.test.ts
+++ b/e2e/components/SelectPanel.test.ts
@@ -108,4 +108,24 @@ test.describe('SelectPanel', () => {
       `SelectPanel-Default-forced-colors-dark-modern-action-list--true.png`,
     )
   })
+
+  test(`Default @vrt responsive width .modern-action-list--true`, async ({page}) => {
+    await visit(page, {
+      id: 'components-selectpanel--default',
+      globals: {featureFlags: {primer_react_select_panel_with_modern_action_list: true}},
+    })
+
+    await page.setViewportSize({width: 767, height: 767})
+
+    // Open select panel
+    const isPanelOpen = await page.isVisible('[role="listbox"]')
+    if (!isPanelOpen) {
+      await page.keyboard.press('Tab')
+      await page.keyboard.press('Enter')
+    }
+
+    expect(await page.screenshot({animations: 'disabled'})).toMatchSnapshot(
+      `SelectPanel-Default-responsive-width-light-modern-action-list--true.png`,
+    )
+  })
 })
diff --git a/packages/react/src/AnchoredOverlay/AnchoredOverlay.docs.json b/packages/react/src/AnchoredOverlay/AnchoredOverlay.docs.json
index 4ecfb62eb2a..8d52c6955ef 100644
--- a/packages/react/src/AnchoredOverlay/AnchoredOverlay.docs.json
+++ b/packages/react/src/AnchoredOverlay/AnchoredOverlay.docs.json
@@ -147,12 +147,20 @@
       "required": false,
       "description": "",
       "defaultValue": ""
-    },    {
+    },
+    {
       "name": "pinPosition",
       "type": "boolean",
       "required": false,
       "description": "If true, the overlay will attempt to prevent position shifting when sitting at the top of the anchor.",
       "defaultValue": "false"
+    },
+    {
+      "name": "variant",
+      "type": "{ regular?: 'anchored', narrow?: 'anchored' | 'fullscreen' }",
+      "required": false,
+      "description": "Optional prop to set variant for narrow screen sizes",
+      "defaultValue": "{ regular: 'anchored', narrow: 'anchored' }"
     }
   ]
 }
diff --git a/packages/react/src/AnchoredOverlay/AnchoredOverlay.tsx b/packages/react/src/AnchoredOverlay/AnchoredOverlay.tsx
index 5f69fcb168f..cb4de3af3a3 100644
--- a/packages/react/src/AnchoredOverlay/AnchoredOverlay.tsx
+++ b/packages/react/src/AnchoredOverlay/AnchoredOverlay.tsx
@@ -8,6 +8,7 @@ import {useFocusZone} from '../hooks/useFocusZone'
 import {useAnchoredPosition, useProvidedRefOrCreate, useRenderForcingRef} from '../hooks'
 import {useId} from '../hooks/useId'
 import type {PositionSettings} from '@primer/behaviors'
+import {useResponsiveValue, type ResponsiveValue} from '../hooks/useResponsiveValue'
 
 interface AnchoredOverlayPropsWithAnchor {
   /**
@@ -93,6 +94,10 @@ interface AnchoredOverlayBaseProps extends Pick<OverlayProps, 'height' | 'width'
    * If true, the overlay will attempt to prevent position shifting when sitting at the top of the anchor.
    */
   pinPosition?: boolean
+  /**
+   * Optional prop to set variant for narrow screen sizes
+   */
+  variant?: ResponsiveValue<'anchored', 'anchored' | 'fullscreen'>
 }
 
 export type AnchoredOverlayProps = AnchoredOverlayBaseProps &
@@ -122,6 +127,7 @@ export const AnchoredOverlay: React.FC<React.PropsWithChildren<AnchoredOverlayPr
   anchorOffset,
   className,
   pinPosition,
+  variant = {regular: 'anchored', narrow: 'anchored'},
   preventOverflow = true,
 }) => {
   const anchorRef = useProvidedRefOrCreate(externalAnchorRef)
@@ -183,6 +189,8 @@ export const AnchoredOverlay: React.FC<React.PropsWithChildren<AnchoredOverlayPr
   })
   useFocusTrap({containerRef: overlayRef, disabled: !open || !position, ...focusTrapSettings})
 
+  const currentResponsiveVariant = useResponsiveValue(variant, 'anchored')
+
   return (
     <>
       {renderAnchor &&
@@ -206,8 +214,9 @@ export const AnchoredOverlay: React.FC<React.PropsWithChildren<AnchoredOverlayPr
           visibility={position ? 'visible' : 'hidden'}
           height={height}
           width={width}
-          top={position?.top || 0}
-          left={position?.left || 0}
+          top={currentResponsiveVariant === 'anchored' ? position?.top || 0 : undefined}
+          left={currentResponsiveVariant === 'anchored' ? position?.left || 0 : undefined}
+          data-variant={currentResponsiveVariant}
           anchorSide={position?.anchorSide}
           className={className}
           preventOverflow={preventOverflow}
diff --git a/packages/react/src/ConfirmationDialog/ConfirmationDialog.test.tsx b/packages/react/src/ConfirmationDialog/ConfirmationDialog.test.tsx
index 87154070a08..bd9de14a80b 100644
--- a/packages/react/src/ConfirmationDialog/ConfirmationDialog.test.tsx
+++ b/packages/react/src/ConfirmationDialog/ConfirmationDialog.test.tsx
@@ -10,6 +10,9 @@ import {ConfirmationDialog, useConfirm} from './ConfirmationDialog'
 import theme from '../theme'
 import {ThemeProvider} from '../ThemeProvider'
 import {behavesAsComponent, checkExports} from '../utils/testing'
+import {setupMatchMedia} from '../utils/test-helpers'
+
+setupMatchMedia() // need to mock media for deprecated/ActionMenu
 
 const Basic = ({confirmButtonType}: Pick<React.ComponentProps<typeof ConfirmationDialog>, 'confirmButtonType'>) => {
   const [isOpen, setIsOpen] = useState(false)
diff --git a/packages/react/src/Overlay/Overlay.module.css b/packages/react/src/Overlay/Overlay.module.css
index 113d82b8bc5..5aab9024d0a 100644
--- a/packages/react/src/Overlay/Overlay.module.css
+++ b/packages/react/src/Overlay/Overlay.module.css
@@ -156,4 +156,13 @@
   &:where([data-visibility-hidden]) {
     visibility: hidden;
   }
+
+  &:where([data-variant='fullscreen']) {
+    top: 0;
+    left: 0;
+    width: 100vw;
+    height: 100vh;
+    margin: 0;
+    border-radius: unset;
+  }
 }
diff --git a/packages/react/src/Overlay/Overlay.test.tsx b/packages/react/src/Overlay/Overlay.test.tsx
index f52ebaba446..66cbb7982b2 100644
--- a/packages/react/src/Overlay/Overlay.test.tsx
+++ b/packages/react/src/Overlay/Overlay.test.tsx
@@ -8,6 +8,9 @@ import BaseStyles from '../BaseStyles'
 import {ThemeProvider} from '../ThemeProvider'
 import {NestedOverlays, MemexNestedOverlays, MemexIssueOverlay, PositionedOverlays} from './Overlay.features.stories'
 import {FeatureFlags} from '../FeatureFlags'
+import {setupMatchMedia} from '../utils/test-helpers'
+
+setupMatchMedia()
 
 type TestComponentSettings = {
   initialFocus?: 'button'
diff --git a/packages/react/src/Overlay/Overlay.tsx b/packages/react/src/Overlay/Overlay.tsx
index d3bedcfeb21..519be0d24f4 100644
--- a/packages/react/src/Overlay/Overlay.tsx
+++ b/packages/react/src/Overlay/Overlay.tsx
@@ -103,6 +103,15 @@ const StyledOverlay = toggleStyledComponent(
       max-width: calc(100vw - 2rem);
     }
 
+    &:where([data-variant='fullscreen']) {
+      top: 0;
+      left: 0;
+      width: 100vw;
+      height: 100vh;
+      margin: 0;
+      border-radius: unset;
+    }
+
     ${sx};
   `,
 )
diff --git a/packages/react/src/SelectPanel/SelectPanel.test.tsx b/packages/react/src/SelectPanel/SelectPanel.test.tsx
index 8e7cb169127..877fa43ba19 100644
--- a/packages/react/src/SelectPanel/SelectPanel.test.tsx
+++ b/packages/react/src/SelectPanel/SelectPanel.test.tsx
@@ -10,6 +10,9 @@ import {getLiveRegion} from '../utils/testing'
 import {IconButton} from '../Button'
 import {ArrowLeftIcon} from '@primer/octicons-react'
 import Box from '../Box'
+import {setupMatchMedia} from '../utils/test-helpers'
+
+setupMatchMedia()
 
 const renderWithFlag = (children: React.ReactNode, flag: boolean) => {
   return render(
diff --git a/packages/react/src/TooltipV2/__tests__/Tooltip.test.tsx b/packages/react/src/TooltipV2/__tests__/Tooltip.test.tsx
index e832be1ec9c..c019df7c042 100644
--- a/packages/react/src/TooltipV2/__tests__/Tooltip.test.tsx
+++ b/packages/react/src/TooltipV2/__tests__/Tooltip.test.tsx
@@ -6,6 +6,9 @@ import {render as HTMLRender} from '@testing-library/react'
 import theme from '../../theme'
 import {Button, IconButton, ActionMenu, ActionList, ThemeProvider, BaseStyles, ButtonGroup} from '../..'
 import {XIcon} from '@primer/octicons-react'
+import {setupMatchMedia} from '../../utils/test-helpers'
+
+setupMatchMedia()
 
 const TooltipComponent = (props: Omit<TooltipProps, 'text'> & {text?: string}) => (
   <Tooltip text="Tooltip text" {...props}>
diff --git a/packages/react/src/__tests__/ActionMenu.test.tsx b/packages/react/src/__tests__/ActionMenu.test.tsx
index 29b4e165dea..64b488b2679 100644
--- a/packages/react/src/__tests__/ActionMenu.test.tsx
+++ b/packages/react/src/__tests__/ActionMenu.test.tsx
@@ -10,6 +10,9 @@ import {behavesAsComponent, checkExports} from '../utils/testing'
 import {SingleSelect} from '../ActionMenu/ActionMenu.features.stories'
 import {MixedSelection} from '../ActionMenu/ActionMenu.examples.stories'
 import {SearchIcon, KebabHorizontalIcon} from '@primer/octicons-react'
+import {setupMatchMedia} from '../utils/test-helpers'
+
+setupMatchMedia()
 
 function Example(): JSX.Element {
   return (
diff --git a/packages/react/src/__tests__/AnchoredOverlay.test.tsx b/packages/react/src/__tests__/AnchoredOverlay.test.tsx
index 761a1597390..e79514a04ef 100644
--- a/packages/react/src/__tests__/AnchoredOverlay.test.tsx
+++ b/packages/react/src/__tests__/AnchoredOverlay.test.tsx
@@ -7,6 +7,9 @@ import {Button} from '../Button'
 import theme from '../theme'
 import BaseStyles from '../BaseStyles'
 import {ThemeProvider} from '../ThemeProvider'
+import {setupMatchMedia} from '../utils/test-helpers'
+
+setupMatchMedia()
 
 type TestComponentSettings = {
   initiallyOpen?: boolean
diff --git a/packages/react/src/__tests__/LabelGroup.test.tsx b/packages/react/src/__tests__/LabelGroup.test.tsx
index 77a89f65581..dc48c8fe1d3 100644
--- a/packages/react/src/__tests__/LabelGroup.test.tsx
+++ b/packages/react/src/__tests__/LabelGroup.test.tsx
@@ -5,6 +5,9 @@ import {LabelGroup, Label, ThemeProvider, BaseStyles} from '..'
 import {behavesAsComponent, checkExports} from '../utils/testing'
 import theme from '../theme'
 import userEvent from '@testing-library/user-event'
+import {setupMatchMedia} from '../utils/test-helpers'
+
+setupMatchMedia()
 
 const ThemeAndStyleContainer: React.FC<React.PropsWithChildren> = ({children}) => (
   <ThemeProvider theme={theme}>
diff --git a/packages/react/src/__tests__/__snapshots__/AnchoredOverlay.test.tsx.snap b/packages/react/src/__tests__/__snapshots__/AnchoredOverlay.test.tsx.snap
index 169fa86efef..ce4d66ef15a 100644
--- a/packages/react/src/__tests__/__snapshots__/AnchoredOverlay.test.tsx.snap
+++ b/packages/react/src/__tests__/__snapshots__/AnchoredOverlay.test.tsx.snap
@@ -30,6 +30,15 @@ exports[`AnchoredOverlay should render consistently when open 1`] = `
   max-width: calc(100vw - 2rem);
 }
 
+.c1:where([data-variant='fullscreen']) {
+  top: 0;
+  left: 0;
+  width: 100vw;
+  height: 100vh;
+  margin: 0;
+  border-radius: unset;
+}
+
 @media (forced-colors:active) {
   .c1 {
     outline: solid 1px transparent;
@@ -82,6 +91,7 @@ exports[`AnchoredOverlay should render consistently when open 1`] = `
         <div
           class="c1"
           data-focus-trap="active"
+          data-variant="anchored"
           height="auto"
           role="none"
           style="left: 0px; top: 4px; --styled-overlay-visibility: visible;"
diff --git a/packages/react/src/__tests__/deprecated/ActionMenu.test.tsx b/packages/react/src/__tests__/deprecated/ActionMenu.test.tsx
index d801d8309c3..adc4aa25293 100644
--- a/packages/react/src/__tests__/deprecated/ActionMenu.test.tsx
+++ b/packages/react/src/__tests__/deprecated/ActionMenu.test.tsx
@@ -6,6 +6,9 @@ import {ActionMenu} from '../../deprecated'
 import {behavesAsComponent, checkExports} from '../../utils/testing'
 import {BaseStyles, ThemeProvider} from '../..'
 import type {ItemProps} from '../../deprecated/ActionList/Item'
+import {setupMatchMedia} from '../../utils/test-helpers'
+
+setupMatchMedia()
 
 const items = [
   {text: 'New file'},
diff --git a/packages/react/src/utils/test-helpers.tsx b/packages/react/src/utils/test-helpers.tsx
index 52525c44008..4f7125c45c6 100644
--- a/packages/react/src/utils/test-helpers.tsx
+++ b/packages/react/src/utils/test-helpers.tsx
@@ -47,3 +47,23 @@ if (typeof document !== 'undefined') {
 if (global.Element.prototype.scrollIntoView === undefined) {
   global.Element.prototype.scrollIntoView = jest.fn()
 }
+
+// setup match media for tests that use useResponsiveValue or use a compone that uses useResponsiveValue
+// we don't set this up globally for all tests because some tests need to be able mock matchMedia with more granular control
+export const setupMatchMedia = () => {
+  // window.matchMedia() is not implemented by JSDOM so we have to create a mock:
+  // https://jestjs.io/docs/manual-mocks#mocking-methods-which-are-not-implemented-in-jsdom
+  Object.defineProperty(window, 'matchMedia', {
+    writable: true,
+    value: jest.fn().mockImplementation(query => ({
+      matches: false,
+      media: query,
+      onchange: null,
+      addListener: jest.fn(), // deprecated
+      removeListener: jest.fn(), // deprecated
+      addEventListener: jest.fn(),
+      removeEventListener: jest.fn(),
+      dispatchEvent: jest.fn(),
+    })),
+  })
+}