diff --git a/packages/app/src/components/composer-height-mirror.web.ts b/packages/app/src/components/composer-height-mirror.web.ts
index 58ddbb277..c24b49b0d 100644
--- a/packages/app/src/components/composer-height-mirror.web.ts
+++ b/packages/app/src/components/composer-height-mirror.web.ts
@@ -98,13 +98,19 @@ export function useComposerHeightMirror({
 
   useLayoutEffect(() => {
     measure();
-  }, [value, measure]);
+  }, [maxHeight, minHeight, value, measure]);
 
   useEffect(() => {
     const source = textareaRef.current;
     if (!source || !(source instanceof HTMLElement)) return;
     if (typeof ResizeObserver === "undefined") return;
-    const observer = new ResizeObserver(() => measure());
+    let previousWidth = source.clientWidth;
+    const observer = new ResizeObserver(() => {
+      const nextWidth = source.clientWidth;
+      if (Math.abs(nextWidth - previousWidth) < 1) return;
+      previousWidth = nextWidth;
+      measure();
+    });
     observer.observe(source);
     return () => observer.disconnect();
   }, [textareaRef, measure]);
diff --git a/packages/app/src/components/message-input.tsx b/packages/app/src/components/message-input.tsx
index e921e071e..3fc41f11d 100644
--- a/packages/app/src/components/message-input.tsx
+++ b/packages/app/src/components/message-input.tsx
@@ -3,6 +3,7 @@ import {
   Text,
   TextInput,
   ActivityIndicator,
+  useWindowDimensions,
   NativeSyntheticEvent,
   TextInputContentSizeChangeEventData,
   TextInputKeyPressEventData,
@@ -144,7 +145,8 @@ export interface MessageInputRef {
 
 const MIN_INPUT_HEIGHT_MOBILE = 30;
 const MIN_INPUT_HEIGHT_DESKTOP = 46;
-const MAX_INPUT_HEIGHT = 160;
+const DEFAULT_MAX_INPUT_HEIGHT = 160;
+const MAX_INPUT_VIEWPORT_RATIO = 0.5;
 const MIN_INPUT_HEIGHT = isWeb ? MIN_INPUT_HEIGHT_DESKTOP : MIN_INPUT_HEIGHT_MOBILE;
 
 type WebTextInputKeyPressEvent = NativeSyntheticEvent<
@@ -983,17 +985,22 @@ function computeIsDictationStartEnabled(
   return (isReadyForDictation ?? isConnected) && !disabled;
 }
 
-function computeTextInputHeightStyle(inputHeight: number) {
+function resolveMaxInputHeight(windowHeight: number): number {
+  if (!Number.isFinite(windowHeight) || windowHeight <= 0) return DEFAULT_MAX_INPUT_HEIGHT;
+  return Math.max(DEFAULT_MAX_INPUT_HEIGHT, Math.floor(windowHeight * MAX_INPUT_VIEWPORT_RATIO));
+}
+
+function computeTextInputHeightStyle(inputHeight: number, maxInputHeight: number) {
   if (isWeb) {
     return {
       height: inputHeight,
       minHeight: MIN_INPUT_HEIGHT,
-      maxHeight: MAX_INPUT_HEIGHT,
+      maxHeight: maxInputHeight,
     };
   }
   return {
     minHeight: MIN_INPUT_HEIGHT,
-    maxHeight: MAX_INPUT_HEIGHT,
+    maxHeight: maxInputHeight,
   };
 }
 
@@ -1191,6 +1198,8 @@ export const MessageInput = forwardRef<MessageInputRef, MessageInputProps>(
       attachmentSlot,
     } = resolveMessageInputProps(props);
     const isCompact = useIsCompactFormFactor();
+    const { height: windowHeight } = useWindowDimensions();
+    const maxInputHeight = resolveMaxInputHeight(windowHeight);
     const buttonIconSize = isWeb ? ICON_SIZE.md : ICON_SIZE.lg;
     const toast = useToast();
     const voice = useVoiceOptional();
@@ -1522,7 +1531,7 @@ export const MessageInput = forwardRef<MessageInputRef, MessageInputProps>(
     }, [getWebTextArea]);
 
     const inputScrollbar = useWebElementScrollbar(webTextareaRef, {
-      enabled: isWeb && inputHeight >= MAX_INPUT_HEIGHT,
+      enabled: isWeb,
     });
 
     usePasteImagesEffect({
@@ -1536,20 +1545,24 @@ export const MessageInput = forwardRef<MessageInputRef, MessageInputProps>(
 
     const setBoundedInputHeight = useCallback(
       (nextHeight: number) => {
-        const bounded = Math.max(MIN_INPUT_HEIGHT, Math.min(MAX_INPUT_HEIGHT, nextHeight));
+        const bounded = Math.max(MIN_INPUT_HEIGHT, Math.min(maxInputHeight, nextHeight));
         if (Math.abs(inputHeightRef.current - bounded) < 1) return;
         inputHeightRef.current = bounded;
         setInputHeight(bounded);
         onHeightChange?.(bounded);
       },
-      [onHeightChange],
+      [maxInputHeight, onHeightChange],
     );
 
+    useEffect(() => {
+      setBoundedInputHeight(inputHeightRef.current);
+    }, [setBoundedInputHeight]);
+
     useComposerHeightMirror({
       value,
       textareaRef: webTextareaRef,
       minHeight: MIN_INPUT_HEIGHT,
-      maxHeight: MAX_INPUT_HEIGHT,
+      maxHeight: maxInputHeight,
       onHeight: setBoundedInputHeight,
     });
 
@@ -1674,8 +1687,8 @@ export const MessageInput = forwardRef<MessageInputRef, MessageInputProps>(
       [inputWrapperStyle, inputAnimatedStyle],
     );
     const textInputStyle = useMemo(
-      () => [styles.textInput, computeTextInputHeightStyle(inputHeight)],
-      [inputHeight],
+      () => [styles.textInput, computeTextInputHeightStyle(inputHeight, maxInputHeight)],
+      [inputHeight, maxInputHeight],
     );
     const sendButtonCombinedStyle = useMemo(
       () => [styles.sendButton, isSendButtonDisabled && styles.buttonDisabled],
@@ -1727,7 +1740,7 @@ export const MessageInput = forwardRef<MessageInputRef, MessageInputProps>(
               onBlur={handleInputBlur}
               style={textInputStyle}
               multiline
-              scrollEnabled={isWeb ? inputHeight >= MAX_INPUT_HEIGHT : true}
+              scrollEnabled={isWeb ? inputHeight >= maxInputHeight : true}
               onContentSizeChange={handleContentSizeChange}
               editable={!isDictating && !isRealtimeVoiceForCurrentAgent && !disabled}
               onKeyPress={shouldHandleWebKeyPress ? handleDesktopKeyPress : undefined}
diff --git a/packages/app/src/components/use-web-scrollbar.tsx b/packages/app/src/components/use-web-scrollbar.tsx
index febdfbef6..ab6e13e6e 100644
--- a/packages/app/src/components/use-web-scrollbar.tsx
+++ b/packages/app/src/components/use-web-scrollbar.tsx
@@ -1,4 +1,4 @@
-import { useCallback, useEffect, useState, type ReactNode, type RefObject } from "react";
+import { useCallback, useLayoutEffect, useState, type ReactNode, type RefObject } from "react";
 import {
   type FlatList,
   type LayoutChangeEvent,
@@ -21,8 +21,25 @@ function ensureHideScrollbarStyle(): void {
   if (document.getElementById(HIDE_SCROLLBAR_STYLE_ID)) return;
   const style = document.createElement("style");
   style.id = HIDE_SCROLLBAR_STYLE_ID;
-  style.textContent =
-    "[data-hide-scrollbar]::-webkit-scrollbar { display: none; width: 0; height: 0; }";
+  style.textContent = `
+    [data-hide-scrollbar] {
+      scrollbar-width: none;
+      -ms-overflow-style: none;
+      scrollbar-gutter: auto;
+    }
+
+    [data-hide-scrollbar]::-webkit-scrollbar {
+      display: none;
+      width: 0;
+      height: 0;
+    }
+
+    [data-hide-scrollbar]::-webkit-scrollbar-button {
+      display: none;
+      width: 0;
+      height: 0;
+    }
+  `;
   document.head.appendChild(style);
 }
 
@@ -54,18 +71,25 @@ export function useWebElementScrollbar(
     contentSize: 0,
   });
 
-  useEffect(() => {
+  useLayoutEffect(() => {
     if (!enabled) return;
     const element = elementRef.current;
     if (!element) return;
 
+    type ScrollbarStyle = CSSStyleDeclaration & {
+      scrollbarWidth: string;
+      msOverflowStyle: string;
+      scrollbarGutter: string;
+    };
+    const style = element.style as ScrollbarStyle;
+    const previousScrollbarWidth = style.scrollbarWidth;
+    const previousMsOverflowStyle = style.msOverflowStyle;
+    const previousScrollbarGutter = style.scrollbarGutter;
+
     element.setAttribute("data-hide-scrollbar", "");
-    (
-      element.style as CSSStyleDeclaration & { scrollbarWidth: string; msOverflowStyle: string }
-    ).scrollbarWidth = "none";
-    (
-      element.style as CSSStyleDeclaration & { scrollbarWidth: string; msOverflowStyle: string }
-    ).msOverflowStyle = "none";
+    style.scrollbarWidth = "none";
+    style.msOverflowStyle = "none";
+    style.scrollbarGutter = "auto";
     ensureHideScrollbarStyle();
 
     function update() {
@@ -94,12 +118,9 @@ export function useWebElementScrollbar(
       element.removeEventListener("scroll", update);
       resizeObserver.disconnect();
       element.removeAttribute("data-hide-scrollbar");
-      (
-        element.style as CSSStyleDeclaration & { scrollbarWidth: string; msOverflowStyle: string }
-      ).scrollbarWidth = "";
-      (
-        element.style as CSSStyleDeclaration & { scrollbarWidth: string; msOverflowStyle: string }
-      ).msOverflowStyle = "";
+      style.scrollbarWidth = previousScrollbarWidth;
+      style.msOverflowStyle = previousMsOverflowStyle;
+      style.scrollbarGutter = previousScrollbarGutter;
     };
   }, [contentRef, elementRef, enabled]);