diff --git a/packages/react/package.json b/packages/react/package.json
index d4ae30e6638..21c1ee30aa9 100644
--- a/packages/react/package.json
+++ b/packages/react/package.json
@@ -78,7 +78,6 @@
     "@github/relative-time-element": "^4.5.0",
     "@github/tab-container-element": "^4.8.2",
     "@lit-labs/react": "1.2.1",
-    "@oddbird/css-anchor-positioning": "^0.9.0",
     "@oddbird/popover-polyfill": "^0.5.2",
     "@primer/behaviors": "^1.10.2",
     "@primer/live-region-element": "^0.7.1",
diff --git a/packages/react/src/AnchoredOverlay/AnchoredOverlay.module.css b/packages/react/src/AnchoredOverlay/AnchoredOverlay.module.css
index 5edbdb0a043..a20a216393a 100644
--- a/packages/react/src/AnchoredOverlay/AnchoredOverlay.module.css
+++ b/packages/react/src/AnchoredOverlay/AnchoredOverlay.module.css
@@ -19,6 +19,7 @@
     flip-inline,
     flip-block flip-inline;
   position-visibility: anchors-visible;
+  position-try-order: most-inline-size;
   z-index: 100;
   position: fixed !important;
 
@@ -35,23 +36,37 @@
     /* stylelint-disable primer/spacing */
     top: calc(anchor(bottom) + var(--base-size-4));
     left: anchor(left);
+    max-height: calc(100dvh - anchor(bottom) - var(--base-size-4));
+
+    &[data-align='left'] {
+      left: auto;
+      right: anchor(right);
+    }
   }
 
   &[data-side='outside-top'] {
     margin-bottom: var(--base-size-4);
     bottom: anchor(top);
     left: anchor(left);
+    max-height: calc(anchor(top) - var(--base-size-4));
+
+    &[data-align='left'] {
+      left: auto;
+      right: anchor(right);
+    }
   }
 
   &[data-side='outside-left'] {
     right: anchor(left);
     top: anchor(top);
     margin-right: var(--base-size-4);
+    max-height: calc(100dvh - anchor(top));
   }
 
   &[data-side='outside-right'] {
     left: anchor(right);
     top: anchor(top);
     margin-left: var(--base-size-4);
+    max-height: calc(100dvh - anchor(top));
   }
 }
diff --git a/packages/react/src/AnchoredOverlay/AnchoredOverlay.tsx b/packages/react/src/AnchoredOverlay/AnchoredOverlay.tsx
index 65af71b83dd..810b4d9ec2c 100644
--- a/packages/react/src/AnchoredOverlay/AnchoredOverlay.tsx
+++ b/packages/react/src/AnchoredOverlay/AnchoredOverlay.tsx
@@ -125,17 +125,6 @@ export type AnchoredOverlayProps = AnchoredOverlayBaseProps &
   (AnchoredOverlayPropsWithAnchor | AnchoredOverlayPropsWithoutAnchor) &
   Partial<Pick<PositionSettings, 'align' | 'side' | 'anchorOffset' | 'alignmentOffset' | 'displayInViewport'>>
 
-const applyAnchorPositioningPolyfill = async () => {
-  if (typeof window !== 'undefined' && !('anchorName' in document.documentElement.style)) {
-    try {
-      await import('@oddbird/css-anchor-positioning')
-    } catch (e) {
-      // eslint-disable-next-line no-console
-      console.warn('Failed to load CSS anchor positioning polyfill:', e)
-    }
-  }
-}
-
 const defaultVariant = {
   regular: 'anchored',
   narrow: 'anchored',
@@ -173,7 +162,9 @@ export const AnchoredOverlay: React.FC<React.PropsWithChildren<AnchoredOverlayPr
   displayCloseButton = true,
   closeButtonProps = defaultCloseButtonProps,
 }) => {
-  const cssAnchorPositioning = useFeatureFlag('primer_react_css_anchor_positioning')
+  const cssAnchorPositioningFlag = useFeatureFlag('primer_react_css_anchor_positioning')
+  const supportsNativeCSSAnchorPositioning = useRef(false)
+  const cssAnchorPositioning = cssAnchorPositioningFlag && supportsNativeCSSAnchorPositioning.current
   const anchorRef = useProvidedRefOrCreate(externalAnchorRef)
   const [overlayRef, updateOverlayRef] = useRenderForcingRef<HTMLDivElement>()
   const anchorId = useId(externalAnchorId)
@@ -232,19 +223,14 @@ export const AnchoredOverlay: React.FC<React.PropsWithChildren<AnchoredOverlayPr
     [overlayRef.current],
   )
 
-  const hasLoadedAnchorPositioningPolyfill = useRef(false)
-
   useEffect(() => {
+    supportsNativeCSSAnchorPositioning.current = 'anchorName' in document.documentElement.style
+
     // ensure overlay ref gets cleared when closed, so position can reset between closing/re-opening
     if (!open && overlayRef.current) {
       updateOverlayRef(null)
     }
-
-    if (cssAnchorPositioning && !hasLoadedAnchorPositioningPolyfill.current) {
-      applyAnchorPositioningPolyfill()
-      hasLoadedAnchorPositioningPolyfill.current = true
-    }
-  }, [open, overlayRef, updateOverlayRef, cssAnchorPositioning])
+  }, [open, overlayRef, updateOverlayRef])
 
   useFocusZone({
     containerRef: overlayRef,
@@ -282,6 +268,13 @@ export const AnchoredOverlay: React.FC<React.PropsWithChildren<AnchoredOverlayPr
 
     if (!cssAnchorPositioning || !open || !currentOverlay) return
     currentOverlay.style.setProperty('position-anchor', `--anchored-overlay-anchor-${id}`)
+
+    const anchorElement = anchorRef.current
+    if (anchorElement) {
+      const {horizontal} = getDefaultPosition(anchorElement)
+      currentOverlay.setAttribute('data-align', horizontal)
+    }
+
     try {
       if (!currentOverlay.matches(':popover-open')) {
         currentOverlay.showPopover()
@@ -289,7 +282,7 @@ export const AnchoredOverlay: React.FC<React.PropsWithChildren<AnchoredOverlayPr
     } catch {
       // Ignore if popover is already showing or not supported
     }
-  }, [cssAnchorPositioning, open, overlayElement, id, overlayRef])
+  }, [cssAnchorPositioning, open, overlayElement, id, overlayRef, anchorRef])
 
   const showXIcon = onClose && variant.narrow === 'fullscreen' && displayCloseButton
   const XButtonAriaLabelledBy = closeButtonProps['aria-labelledby']
@@ -365,6 +358,23 @@ export const AnchoredOverlay: React.FC<React.PropsWithChildren<AnchoredOverlayPr
   )
 }
 
+function getDefaultPosition(anchorElement: HTMLElement): {vertical: 'top' | 'bottom'; horizontal: 'left' | 'right'} {
+  const rect = anchorElement.getBoundingClientRect()
+  const {innerWidth: vw, innerHeight: vh} = window
+
+  const space = {
+    top: rect.top,
+    bottom: vh - rect.bottom,
+    left: rect.left,
+    right: vw - rect.right,
+  }
+
+  const vertical = space.bottom >= space.top ? 'bottom' : 'top'
+  const horizontal = space.right >= space.left ? 'right' : 'left'
+
+  return {vertical, horizontal}
+}
+
 function assignRef<T>(
   ref: React.MutableRefObject<T | null> | ((instance: T | null) => void) | null | undefined,
   value: T | null,