diff --git a/packages/ui/src/components/prompt-input.tsx b/packages/ui/src/components/prompt-input.tsx
index afd30eb5..e43e2130 100644
--- a/packages/ui/src/components/prompt-input.tsx
+++ b/packages/ui/src/components/prompt-input.tsx
@@ -31,6 +31,15 @@ import {
 } from "../stores/conversation-speech"
 const log = getLogger("actions")
 const LazyUnifiedPicker = lazy(() => import("./unified-picker"))
+const DEFAULT_PROMPT_FIELD_HEIGHT = 104
+const MAX_PROMPT_FIELD_HEIGHT_RATIO = 0.6
+
+type ResizeDragState = {
+  pointerId: number
+  startY: number
+  startHeight: number
+  maxHeight: number
+}
 
 function getConsumedPastedTextAttachmentIds(text: string, attachments: Attachment[]): string[] {
   if (!text || attachments.length === 0) return []
@@ -65,11 +74,16 @@ export default function PromptInput(props: PromptInputProps) {
   const [, setIsFocused] = createSignal(false)
   const [mode, setMode] = createSignal<PromptMode>("normal")
   const [expandState, setExpandState] = createSignal<ExpandState>("normal")
+  const [inputHeight, setInputHeight] = createSignal<number | null>(null)
+  const [isResizing, setIsResizing] = createSignal(false)
   const [isFileBrowserOpen, setIsFileBrowserOpen] = createSignal(false)
   const SELECTION_INSERT_MAX_LENGTH = 2000
   const MAX_READABLE_PICKED_FILE_BYTES = 5 * 1024 * 1024
   let textareaRef: HTMLTextAreaElement | undefined
   let fileInputRef: HTMLInputElement | undefined
+  let wrapperRef: HTMLDivElement | undefined
+  let fieldContainerRef: HTMLDivElement | undefined
+  let resizeDragState: ResizeDragState | undefined
 
   const getPlaceholder = () => {
     if (mode() === "shell") {
@@ -216,6 +230,7 @@ export default function PromptInput(props: PromptInputProps) {
       draftLoadedNonce,
       () => {
         // Session switch resets (picker/counters/ignored positions) stay in the component.
+        setInputHeight(null)
         setIgnoredAtPositions(new Set<number>())
         setShowPicker(false)
         setPickerMode("mention")
@@ -294,6 +309,61 @@ export default function PromptInput(props: PromptInputProps) {
     })
   })
 
+  function computeMaxFieldHeight(): number {
+    if (typeof window === "undefined") return DEFAULT_PROMPT_FIELD_HEIGHT
+
+    const sessionCenter = wrapperRef?.closest("[data-session-center-width]")
+    const availableHeight = sessionCenter?.getBoundingClientRect().height ?? window.innerHeight
+    const maxHeight = Math.floor(availableHeight * MAX_PROMPT_FIELD_HEIGHT_RATIO)
+    return Math.max(DEFAULT_PROMPT_FIELD_HEIGHT, maxHeight)
+  }
+
+  function handleResizeStart(event: PointerEvent) {
+    event.preventDefault()
+    const target = event.currentTarget as HTMLElement
+
+    resizeDragState = {
+      pointerId: event.pointerId,
+      startY: event.clientY,
+      startHeight: fieldContainerRef?.getBoundingClientRect().height ?? DEFAULT_PROMPT_FIELD_HEIGHT,
+      maxHeight: computeMaxFieldHeight(),
+    }
+
+    setIsResizing(true)
+
+    try {
+      target.setPointerCapture(event.pointerId)
+    } catch {
+      resizeDragState = undefined
+      setIsResizing(false)
+    }
+  }
+
+  function handleResizeMove(event: PointerEvent) {
+    if (!resizeDragState || resizeDragState.pointerId !== event.pointerId) return
+
+    event.preventDefault()
+    const deltaY = resizeDragState.startY - event.clientY
+    const nextHeight = Math.max(
+      DEFAULT_PROMPT_FIELD_HEIGHT,
+      Math.min(resizeDragState.maxHeight, resizeDragState.startHeight + deltaY),
+    )
+    setInputHeight(nextHeight)
+  }
+
+  function handleResizeEnd(event: PointerEvent) {
+    if (!resizeDragState || resizeDragState.pointerId !== event.pointerId) return
+
+    event.preventDefault()
+    resizeDragState = undefined
+    setIsResizing(false)
+    textareaRef?.focus()
+  }
+
+  onCleanup(() => {
+    resizeDragState = undefined
+  })
+
   async function handleSend() {
     const text = prompt().trim()
     const currentAttachments = attachments()
@@ -324,6 +394,7 @@ export default function PromptInput(props: PromptInputProps) {
     const refreshHistory = () => recordHistoryEntry(historyEntry)
 
     setExpandState("normal")
+    setInputHeight(null)
     clearPrompt()
     clearHistoryDraft()
     setMode("normal")
@@ -382,6 +453,7 @@ export default function PromptInput(props: PromptInputProps) {
   }
 
   function handleExpandToggle(nextState: "normal" | "expanded") {
+    setInputHeight(null)
     setExpandState(nextState)
     // Keep focus on textarea
     textareaRef?.focus()
@@ -599,6 +671,7 @@ export default function PromptInput(props: PromptInputProps) {
   return (
     <div class="prompt-input-container">
       <div
+        ref={wrapperRef}
         class={`prompt-input-wrapper relative ${isDragging() ? "border-2" : ""}`}
         style={
           isDragging()
@@ -631,9 +704,26 @@ export default function PromptInput(props: PromptInputProps) {
         </Show>
 
         <div class="prompt-input-main flex flex-1 flex-col">
-          <div class={`prompt-input-field-container ${expandState() === "expanded" ? "is-expanded" : ""}`}>
+          <div
+            ref={fieldContainerRef}
+            class={`prompt-input-field-container ${expandState() === "expanded" ? "is-expanded" : ""} ${inputHeight() !== null ? "is-resized" : ""}`}
+            style={inputHeight() !== null ? { height: `${inputHeight()}px`, "min-height": `${inputHeight()}px` } : undefined}
+          >
+            <div
+              class={`prompt-resize-handle ${isResizing() ? "is-resizing" : ""}`}
+              onPointerDown={handleResizeStart}
+              onPointerMove={handleResizeMove}
+              onPointerUp={handleResizeEnd}
+              onPointerCancel={handleResizeEnd}
+              aria-hidden="true"
+              role="presentation"
+              title={t("promptInput.resizeHandle.title")}
+            />
 
-            <div class={`prompt-input-field ${expandState() === "expanded" ? "is-expanded" : ""}`}>
+            <div
+              class={`prompt-input-field ${expandState() === "expanded" ? "is-expanded" : ""}`}
+              style={inputHeight() !== null ? { height: `${inputHeight()}px`, "min-height": `${inputHeight()}px` } : undefined}
+            >
               <textarea
                 ref={textareaRef}
                 class={`prompt-input ${mode() === "shell" ? "shell-mode" : ""} ${expandState() === "expanded" ? "is-expanded" : ""}`}
@@ -651,6 +741,7 @@ export default function PromptInput(props: PromptInputProps) {
                 autocorrect="off"
                 autoCapitalize="off"
                 autocomplete="off"
+                style={inputHeight() !== null ? { height: `${inputHeight()}px`, "min-height": `${inputHeight()}px`, "overflow-y": "auto" } : undefined}
               />
               <button
                 type="button"
diff --git a/packages/ui/src/lib/i18n/messages/en/messaging.ts b/packages/ui/src/lib/i18n/messages/en/messaging.ts
index 63e96fe4..31700b64 100644
--- a/packages/ui/src/lib/i18n/messages/en/messaging.ts
+++ b/packages/ui/src/lib/i18n/messages/en/messaging.ts
@@ -182,4 +182,5 @@ export const messagingMessages = {
   "promptInput.voiceInput.error.permissionDenied": "Microphone access was denied by macOS.",
   "promptInput.voiceInput.error.unsupported": "Voice input is not supported in this browser.",
   "promptInput.voiceInput.error.transcribe": "Unable to transcribe the recorded audio.",
+  "promptInput.resizeHandle.title": "Drag to resize input height",
 } as const
diff --git a/packages/ui/src/lib/i18n/messages/es/messaging.ts b/packages/ui/src/lib/i18n/messages/es/messaging.ts
index 496f1da9..a2e88568 100644
--- a/packages/ui/src/lib/i18n/messages/es/messaging.ts
+++ b/packages/ui/src/lib/i18n/messages/es/messaging.ts
@@ -149,6 +149,7 @@ export const messagingMessages = {
   "promptInput.hints.commands": "Comandos",
   "promptInput.history.previousAriaLabel": "Prompt anterior",
   "promptInput.history.nextAriaLabel": "Siguiente prompt",
+  "promptInput.resizeHandle.title": "Arrastra para cambiar la altura del campo de entrada",
   "promptInput.overlay.newLine": "Nueva línea",
   "promptInput.overlay.send": "Enviar",
   "promptInput.overlay.filesAgents": "Archivos/agentes",
diff --git a/packages/ui/src/lib/i18n/messages/fr/messaging.ts b/packages/ui/src/lib/i18n/messages/fr/messaging.ts
index 42dd878b..c15477e2 100644
--- a/packages/ui/src/lib/i18n/messages/fr/messaging.ts
+++ b/packages/ui/src/lib/i18n/messages/fr/messaging.ts
@@ -149,6 +149,7 @@ export const messagingMessages = {
   "promptInput.hints.commands": "Commandes",
   "promptInput.history.previousAriaLabel": "Prompt précédent",
   "promptInput.history.nextAriaLabel": "Prompt suivant",
+  "promptInput.resizeHandle.title": "Faites glisser pour redimensionner la hauteur de saisie",
   "promptInput.overlay.newLine": "Nouvelle ligne",
   "promptInput.overlay.send": "Envoyer",
   "promptInput.overlay.filesAgents": "Fichiers/agents",
diff --git a/packages/ui/src/lib/i18n/messages/he/messaging.ts b/packages/ui/src/lib/i18n/messages/he/messaging.ts
index 98e2d6e7..537db2db 100644
--- a/packages/ui/src/lib/i18n/messages/he/messaging.ts
+++ b/packages/ui/src/lib/i18n/messages/he/messaging.ts
@@ -147,6 +147,7 @@ export const messagingMessages = {
   "promptInput.hints.commands": "פקודות",
   "promptInput.history.previousAriaLabel": "פקודה קודמת",
   "promptInput.history.nextAriaLabel": "פקודה הבאה",
+  "promptInput.resizeHandle.title": "גרור כדי לשנות את גובה שדה הקלט",
   "promptInput.overlay.newLine": "שורה חדשה",
   "promptInput.overlay.send": "שלח",
   "promptInput.overlay.filesAgents": "קבצים/סוכנים",
diff --git a/packages/ui/src/lib/i18n/messages/ja/messaging.ts b/packages/ui/src/lib/i18n/messages/ja/messaging.ts
index 39c1da8a..013d9b60 100644
--- a/packages/ui/src/lib/i18n/messages/ja/messaging.ts
+++ b/packages/ui/src/lib/i18n/messages/ja/messaging.ts
@@ -149,6 +149,7 @@ export const messagingMessages = {
   "promptInput.hints.commands": "コマンド",
   "promptInput.history.previousAriaLabel": "前のプロンプト",
   "promptInput.history.nextAriaLabel": "次のプロンプト",
+  "promptInput.resizeHandle.title": "ドラッグして入力欄の高さを変更",
   "promptInput.overlay.newLine": "改行",
   "promptInput.overlay.send": "送信",
   "promptInput.overlay.filesAgents": "ファイル/エージェント",
diff --git a/packages/ui/src/lib/i18n/messages/ru/messaging.ts b/packages/ui/src/lib/i18n/messages/ru/messaging.ts
index c22eb7f9..a4ce41f2 100644
--- a/packages/ui/src/lib/i18n/messages/ru/messaging.ts
+++ b/packages/ui/src/lib/i18n/messages/ru/messaging.ts
@@ -149,6 +149,7 @@ export const messagingMessages = {
   "promptInput.hints.commands": "Команды",
   "promptInput.history.previousAriaLabel": "Предыдущий prompt",
   "promptInput.history.nextAriaLabel": "Следующий prompt",
+  "promptInput.resizeHandle.title": "Перетащите, чтобы изменить высоту поля ввода",
   "promptInput.overlay.newLine": "Новая строка",
   "promptInput.overlay.send": "Отправить",
   "promptInput.overlay.filesAgents": "Файлы/агенты",
diff --git a/packages/ui/src/lib/i18n/messages/zh-Hans/messaging.ts b/packages/ui/src/lib/i18n/messages/zh-Hans/messaging.ts
index 086aa1a6..b00f7e67 100644
--- a/packages/ui/src/lib/i18n/messages/zh-Hans/messaging.ts
+++ b/packages/ui/src/lib/i18n/messages/zh-Hans/messaging.ts
@@ -184,4 +184,5 @@ export const messagingMessages = {
   "promptInput.voiceInput.error.permissionDenied": "macOS 已拒绝麦克风访问。",
   "promptInput.voiceInput.error.unsupported": "此浏览器不支持语音输入。",
   "promptInput.voiceInput.error.transcribe": "无法转写录制的音频。",
+  "promptInput.resizeHandle.title": "拖动以调整输入框高度",
 } as const
diff --git a/packages/ui/src/styles/messaging/prompt-input.css b/packages/ui/src/styles/messaging/prompt-input.css
index c22c495e..b24cb572 100644
--- a/packages/ui/src/styles/messaging/prompt-input.css
+++ b/packages/ui/src/styles/messaging/prompt-input.css
@@ -4,6 +4,47 @@
   background-color: var(--surface-base);
 }
 
+.prompt-resize-handle {
+  position: absolute;
+  top: 0;
+  left: 50%;
+  width: 72px;
+  height: 10px;
+  transform: translateX(-50%);
+  cursor: ns-resize;
+  touch-action: none;
+  z-index: 10;
+  background: transparent;
+}
+
+.prompt-resize-handle::after {
+  content: "";
+  position: absolute;
+  top: 2px;
+  left: 50%;
+  transform: translateX(-50%);
+  width: 40px;
+  height: 2px;
+  border-radius: 1px;
+  background-color: var(--border-base);
+  opacity: 0.5;
+  transition:
+    opacity 0.15s ease,
+    background-color 0.15s ease;
+}
+
+.prompt-resize-handle:hover::after,
+.prompt-resize-handle.is-resizing::after {
+  opacity: 1;
+  background-color: var(--accent-primary);
+}
+
+@media (pointer: coarse) {
+  .prompt-resize-handle {
+    display: none;
+  }
+}
+
 .prompt-input-wrapper {
   --prompt-input-compact-height: 104px;
   @apply grid items-stretch;
@@ -79,6 +120,16 @@
   overflow-y: auto;
 }
 
+.prompt-input-field-container.is-resized .prompt-input-field {
+  height: 100%;
+}
+
+.prompt-input-field-container.is-resized .prompt-input {
+  height: 100%;
+  min-height: 100%;
+  overflow-y: auto;
+}
+
 .prompt-input-overlay {
   position: absolute;
   bottom: 1rem;