diff --git a/packages/app/src/context/settings.tsx b/packages/app/src/context/settings.tsx
index afd03365eacc..e152abf68b43 100644
--- a/packages/app/src/context/settings.tsx
+++ b/packages/app/src/context/settings.tsx
@@ -24,6 +24,7 @@ export interface Settings {
     releaseNotes: boolean
     followup: "queue" | "steer"
     showReasoningSummaries: boolean
+    reasoningToolDefaultOpen: boolean
     shellToolPartsExpanded: boolean
     editToolPartsExpanded: boolean
   }
@@ -90,6 +91,7 @@ const defaultSettings: Settings = {
     releaseNotes: true,
     followup: "steer",
     showReasoningSummaries: false,
+    reasoningToolDefaultOpen: true,
     shellToolPartsExpanded: false,
     editToolPartsExpanded: false,
   },
@@ -169,6 +171,13 @@ export const { use: useSettings, provider: SettingsProvider } = createSimpleCont
         setShowReasoningSummaries(value: boolean) {
           setStore("general", "showReasoningSummaries", value)
         },
+        reasoningToolDefaultOpen: withFallback(
+          () => store.general?.reasoningToolDefaultOpen,
+          defaultSettings.general.reasoningToolDefaultOpen,
+        ),
+        setReasoningToolDefaultOpen(value: boolean) {
+          setStore("general", "reasoningToolDefaultOpen", value)
+        },
         shellToolPartsExpanded: withFallback(
           () => store.general?.shellToolPartsExpanded,
           defaultSettings.general.shellToolPartsExpanded,
diff --git a/packages/app/src/i18n/ar.ts b/packages/app/src/i18n/ar.ts
index 6c3f3bb55ef4..787a8e5f3ab8 100644
--- a/packages/app/src/i18n/ar.ts
+++ b/packages/app/src/i18n/ar.ts
@@ -67,6 +67,9 @@ export const dict = {
   "command.prompt.mode.normal": "Prompt",
   "command.permissions.autoaccept.enable": "قبول الأذونات تلقائيًا",
   "command.permissions.autoaccept.disable": "إيقاف قبول الأذونات تلقائيًا",
+  "command.settings.thinking.enable": "إظهار التفكير",
+  "command.settings.thinking.disable": "إخفاء التفكير",
+  "command.settings.thinking.description": "تبديل عرض ملخصات تفكير النموذج في الجدول الزمني",
   "command.workspace.toggle": "تبديل مساحات العمل",
   "command.workspace.toggle.description": "تمكين أو تعطيل مساحات العمل المتعددة في الشريط الجانبي",
   "command.session.undo": "تراجع",
diff --git a/packages/app/src/i18n/br.ts b/packages/app/src/i18n/br.ts
index 63880462a467..8c07fbdbbd29 100644
--- a/packages/app/src/i18n/br.ts
+++ b/packages/app/src/i18n/br.ts
@@ -67,6 +67,9 @@ export const dict = {
   "command.prompt.mode.normal": "Prompt",
   "command.permissions.autoaccept.enable": "Aceitar permissões automaticamente",
   "command.permissions.autoaccept.disable": "Parar de aceitar permissões automaticamente",
+  "command.settings.thinking.enable": "Mostrar raciocínio",
+  "command.settings.thinking.disable": "Ocultar raciocínio",
+  "command.settings.thinking.description": "Alternar exibição de resumos de raciocínio do modelo na linha do tempo",
   "command.workspace.toggle": "Alternar espaços de trabalho",
   "command.workspace.toggle.description": "Habilitar ou desabilitar múltiplos espaços de trabalho na barra lateral",
   "command.session.undo": "Desfazer",
diff --git a/packages/app/src/i18n/bs.ts b/packages/app/src/i18n/bs.ts
index 2b589eb35f62..e286d8e39fd6 100644
--- a/packages/app/src/i18n/bs.ts
+++ b/packages/app/src/i18n/bs.ts
@@ -73,6 +73,9 @@ export const dict = {
   "command.prompt.mode.normal": "Prompt",
   "command.permissions.autoaccept.enable": "Automatski prihvati dozvole",
   "command.permissions.autoaccept.disable": "Zaustavi automatsko prihvatanje dozvola",
+  "command.settings.thinking.enable": "Prikaži razmišljanje",
+  "command.settings.thinking.disable": "Sakrij razmišljanje",
+  "command.settings.thinking.description": "Uključi/isključi prikaz sažetaka razmišljanja modela na vremenskoj traci",
   "command.workspace.toggle": "Prikaži/sakrij radne prostore",
   "command.workspace.toggle.description": "Omogući ili onemogući više radnih prostora u bočnoj traci",
   "command.session.undo": "Poništi",
diff --git a/packages/app/src/i18n/da.ts b/packages/app/src/i18n/da.ts
index b096d87b4b7b..cc2002e61181 100644
--- a/packages/app/src/i18n/da.ts
+++ b/packages/app/src/i18n/da.ts
@@ -73,6 +73,9 @@ export const dict = {
   "command.prompt.mode.normal": "Prompt",
   "command.permissions.autoaccept.enable": "Accepter tilladelser automatisk",
   "command.permissions.autoaccept.disable": "Stop med at acceptere tilladelser automatisk",
+  "command.settings.thinking.enable": "Vis tænkning",
+  "command.settings.thinking.disable": "Skjul tænkning",
+  "command.settings.thinking.description": "Skift visning af model-tænkningssammendrag på tidslinjen",
   "command.workspace.toggle": "Skift arbejdsområder",
   "command.workspace.toggle.description": "Aktiver eller deaktiver flere arbejdsområder i sidebjælken",
   "command.session.undo": "Fortryd",
diff --git a/packages/app/src/i18n/de.ts b/packages/app/src/i18n/de.ts
index 6dc0b0497245..a9e306efe6ff 100644
--- a/packages/app/src/i18n/de.ts
+++ b/packages/app/src/i18n/de.ts
@@ -71,6 +71,9 @@ export const dict = {
   "command.prompt.mode.normal": "Prompt",
   "command.permissions.autoaccept.enable": "Berechtigungen automatisch akzeptieren",
   "command.permissions.autoaccept.disable": "Automatische Akzeptanz von Berechtigungen stoppen",
+  "command.settings.thinking.enable": "Denken anzeigen",
+  "command.settings.thinking.disable": "Denken ausblenden",
+  "command.settings.thinking.description": "Anzeige der Denkzusammenfassungen des Modells in der Zeitleiste umschalten",
   "command.workspace.toggle": "Arbeitsbereiche umschalten",
   "command.workspace.toggle.description": "Mehrere Arbeitsbereiche in der Seitenleiste aktivieren oder deaktivieren",
   "command.session.undo": "Rückgängig",
diff --git a/packages/app/src/i18n/en.ts b/packages/app/src/i18n/en.ts
index c6bcc37b116f..0b7dff1f25af 100644
--- a/packages/app/src/i18n/en.ts
+++ b/packages/app/src/i18n/en.ts
@@ -75,6 +75,9 @@ export const dict = {
   "command.prompt.mode.normal": "Prompt",
   "command.permissions.autoaccept.enable": "Auto-accept permissions",
   "command.permissions.autoaccept.disable": "Stop auto-accepting permissions",
+  "command.settings.thinking.enable": "Show reasoning",
+  "command.settings.thinking.disable": "Hide reasoning",
+  "command.settings.thinking.description": "Toggle whether to show model reasoning summaries in the timeline",
   "command.workspace.toggle": "Toggle workspaces",
   "command.workspace.toggle.description": "Enable or disable multiple workspaces in the sidebar",
   "command.session.undo": "Undo",
diff --git a/packages/app/src/i18n/es.ts b/packages/app/src/i18n/es.ts
index c600232ef613..bba9ec7c1435 100644
--- a/packages/app/src/i18n/es.ts
+++ b/packages/app/src/i18n/es.ts
@@ -73,6 +73,10 @@ export const dict = {
   "command.prompt.mode.normal": "Prompt",
   "command.permissions.autoaccept.enable": "Aceptar permisos automáticamente",
   "command.permissions.autoaccept.disable": "Dejar de aceptar permisos automáticamente",
+  "command.settings.thinking.enable": "Mostrar razonamiento",
+  "command.settings.thinking.disable": "Ocultar razonamiento",
+  "command.settings.thinking.description":
+    "Alternar la visualización de resúmenes de razonamiento del modelo en la línea de tiempo",
   "command.workspace.toggle": "Alternar espacios de trabajo",
   "command.workspace.toggle.description": "Habilitar o deshabilitar múltiples espacios de trabajo en la barra lateral",
   "command.session.undo": "Deshacer",
diff --git a/packages/app/src/i18n/fr.ts b/packages/app/src/i18n/fr.ts
index a140c1e3a123..7f106478a093 100644
--- a/packages/app/src/i18n/fr.ts
+++ b/packages/app/src/i18n/fr.ts
@@ -67,8 +67,10 @@ export const dict = {
   "command.prompt.mode.normal": "Prompt",
   "command.permissions.autoaccept.enable": "Accepter automatiquement les permissions",
   "command.permissions.autoaccept.disable": "Arrêter d'accepter automatiquement les permissions",
-  "command.workspace.toggle": "Basculer les espaces de travail",
-  "command.workspace.toggle.description": "Activer ou désactiver plusieurs espaces de travail dans la barre latérale",
+  "command.settings.thinking.enable": "Afficher le raisonnement",
+  "command.settings.thinking.disable": "Masquer le raisonnement",
+  "command.settings.thinking.description":
+    "Basculer l'affichage des résumés de raisonnement du modèle dans la chronologie",
   "command.session.undo": "Annuler",
   "command.session.undo.description": "Annuler le dernier message",
   "command.session.redo": "Rétablir",
diff --git a/packages/app/src/i18n/ja.ts b/packages/app/src/i18n/ja.ts
index 3da1c4b43b58..019204eb816b 100644
--- a/packages/app/src/i18n/ja.ts
+++ b/packages/app/src/i18n/ja.ts
@@ -67,8 +67,9 @@ export const dict = {
   "command.prompt.mode.normal": "プロンプト",
   "command.permissions.autoaccept.enable": "権限を自動承認する",
   "command.permissions.autoaccept.disable": "権限の自動承認を停止する",
-  "command.workspace.toggle": "ワークスペースを切り替え",
-  "command.workspace.toggle.description": "サイドバーでの複数のワークスペースの有効化・無効化",
+  "command.settings.thinking.enable": "思考を表示",
+  "command.settings.thinking.disable": "思考を非表示",
+  "command.settings.thinking.description": "タイムライン内のモデルの思考要約の表示を切り替え",
   "command.session.undo": "元に戻す",
   "command.session.undo.description": "最後のメッセージを元に戻す",
   "command.session.redo": "やり直す",
diff --git a/packages/app/src/i18n/ko.ts b/packages/app/src/i18n/ko.ts
index 0f2f7647abf5..10b8f2f4a020 100644
--- a/packages/app/src/i18n/ko.ts
+++ b/packages/app/src/i18n/ko.ts
@@ -71,6 +71,9 @@ export const dict = {
   "command.prompt.mode.normal": "프롬프트",
   "command.permissions.autoaccept.enable": "권한 자동 수락",
   "command.permissions.autoaccept.disable": "권한 자동 수락 중지",
+  "command.settings.thinking.enable": "사고 표시",
+  "command.settings.thinking.disable": "사고 숨기기",
+  "command.settings.thinking.description": "타임라인에서 모델 사고 요약 표시 전환",
   "command.workspace.toggle": "작업 공간 전환",
   "command.workspace.toggle.description": "사이드바에서 다중 작업 공간 활성화 또는 비활성화",
   "command.session.undo": "실행 취소",
diff --git a/packages/app/src/i18n/no.ts b/packages/app/src/i18n/no.ts
index a0a968179cd0..639c4b17368b 100644
--- a/packages/app/src/i18n/no.ts
+++ b/packages/app/src/i18n/no.ts
@@ -76,6 +76,9 @@ export const dict = {
   "command.prompt.mode.normal": "Prompt",
   "command.permissions.autoaccept.enable": "Aksepter tillatelser automatisk",
   "command.permissions.autoaccept.disable": "Stopp automatisk akseptering av tillatelser",
+  "command.settings.thinking.enable": "Vis tenkning",
+  "command.settings.thinking.disable": "Skjul tenkning",
+  "command.settings.thinking.description": "Veksle visning av modellens tenkesammendrag i tidslinjen",
   "command.workspace.toggle": "Veksle arbeidsområder",
   "command.workspace.toggle.description": "Enable or disable multiple workspaces in the sidebar",
   "command.session.undo": "Angre",
diff --git a/packages/app/src/i18n/pl.ts b/packages/app/src/i18n/pl.ts
index 88d209f11ff2..f2e5171a8990 100644
--- a/packages/app/src/i18n/pl.ts
+++ b/packages/app/src/i18n/pl.ts
@@ -67,8 +67,9 @@ export const dict = {
   "command.prompt.mode.normal": "Prompt",
   "command.permissions.autoaccept.enable": "Automatycznie akceptuj uprawnienia",
   "command.permissions.autoaccept.disable": "Zatrzymaj automatyczne akceptowanie uprawnień",
-  "command.workspace.toggle": "Przełącz przestrzenie robocze",
-  "command.workspace.toggle.description": "Włącz lub wyłącz wiele przestrzeni roboczych na pasku bocznym",
+  "command.settings.thinking.enable": "Pokaż myślenie",
+  "command.settings.thinking.disable": "Ukryj myślenie",
+  "command.settings.thinking.description": "Przełącz wyświetlanie podsumowań myślenia modelu na osi czasu",
   "command.session.undo": "Cofnij",
   "command.session.undo.description": "Cofnij ostatnią wiadomość",
   "command.session.redo": "Ponów",
diff --git a/packages/app/src/i18n/ru.ts b/packages/app/src/i18n/ru.ts
index 688289b7e812..718b361463fc 100644
--- a/packages/app/src/i18n/ru.ts
+++ b/packages/app/src/i18n/ru.ts
@@ -73,6 +73,9 @@ export const dict = {
   "command.prompt.mode.normal": "Промпт",
   "command.permissions.autoaccept.enable": "Автоматически принимать разрешения",
   "command.permissions.autoaccept.disable": "Остановить автоматическое принятие разрешений",
+  "command.settings.thinking.enable": "Показать размышления",
+  "command.settings.thinking.disable": "Скрыть размышления",
+  "command.settings.thinking.description": "Переключить отображение сводок размышлений модели в ленте",
   "command.workspace.toggle": "Переключить рабочие пространства",
   "command.workspace.toggle.description": "Включить или отключить несколько рабочих пространств в боковой панели",
   "command.session.undo": "Отменить",
diff --git a/packages/app/src/i18n/th.ts b/packages/app/src/i18n/th.ts
index 5decf3adb531..8b88df3d5a2e 100644
--- a/packages/app/src/i18n/th.ts
+++ b/packages/app/src/i18n/th.ts
@@ -73,6 +73,9 @@ export const dict = {
   "command.prompt.mode.normal": "พรอมต์",
   "command.permissions.autoaccept.enable": "ยอมรับสิทธิ์โดยอัตโนมัติ",
   "command.permissions.autoaccept.disable": "หยุดยอมรับสิทธิ์โดยอัตโนมัติ",
+  "command.settings.thinking.enable": "แสดงการคิด",
+  "command.settings.thinking.disable": "ซ่อนการคิด",
+  "command.settings.thinking.description": "สลับการแสดงสรุปการคิดของโมเดลในไทม์ไลน์",
   "command.workspace.toggle": "สลับพื้นที่ทำงาน",
   "command.workspace.toggle.description": "เปิดหรือปิดใช้งานพื้นที่ทำงานหลายรายการในแถบด้านข้าง",
   "command.session.undo": "ยกเลิก",
diff --git a/packages/app/src/i18n/tr.ts b/packages/app/src/i18n/tr.ts
index 6a3ade0d0b07..d800ebf78b45 100644
--- a/packages/app/src/i18n/tr.ts
+++ b/packages/app/src/i18n/tr.ts
@@ -77,6 +77,9 @@ export const dict = {
   "command.prompt.mode.normal": "Komut",
   "command.permissions.autoaccept.enable": "Düzenlemeleri otomatik kabul et",
   "command.permissions.autoaccept.disable": "Otomatik kabulü durdur",
+  "command.settings.thinking.enable": "Düşünmeyi göster",
+  "command.settings.thinking.disable": "Düşünmeyi gizle",
+  "command.settings.thinking.description": "Zaman çizelgesinde model düşünme özetlerini göster/gizle",
   "command.workspace.toggle": "Çalışma alanlarını aç/kapat",
   "command.workspace.toggle.description": "Kenar çubuğunda birden fazla çalışma alanını göster veya gizle",
   "command.session.undo": "Geri al",
diff --git a/packages/app/src/i18n/zh.ts b/packages/app/src/i18n/zh.ts
index 28231733eaba..60c2a1e301a1 100644
--- a/packages/app/src/i18n/zh.ts
+++ b/packages/app/src/i18n/zh.ts
@@ -99,6 +99,10 @@ export const dict = {
   "command.permissions.autoaccept.enable": "自动接受权限",
   "command.permissions.autoaccept.disable": "停止自动接受权限",
 
+  "command.settings.thinking.enable": "显示思考",
+  "command.settings.thinking.disable": "隐藏思考",
+  "command.settings.thinking.description": "在时间线中切换显示模型思考摘要",
+
   "command.workspace.toggle": "切换工作区",
   "command.workspace.toggle.description": "在侧边栏启用或禁用多个工作区",
 
diff --git a/packages/app/src/i18n/zht.ts b/packages/app/src/i18n/zht.ts
index 4abdf5db574d..0ef2bdf4d9c3 100644
--- a/packages/app/src/i18n/zht.ts
+++ b/packages/app/src/i18n/zht.ts
@@ -77,6 +77,9 @@ export const dict = {
   "command.prompt.mode.normal": "Prompt",
   "command.permissions.autoaccept.enable": "自動接受權限",
   "command.permissions.autoaccept.disable": "停止自動接受權限",
+  "command.settings.thinking.enable": "顯示思考",
+  "command.settings.thinking.disable": "隱藏思考",
+  "command.settings.thinking.description": "在時間軸中切換顯示模型思考摘要",
   "command.workspace.toggle": "切換工作區",
   "command.workspace.toggle.description": "在側邊欄啟用或停用多個工作區",
   "command.session.undo": "復原",
diff --git a/packages/app/src/pages/session/message-timeline.tsx b/packages/app/src/pages/session/message-timeline.tsx
index fe6447c2e8c8..f94d8af6635d 100644
--- a/packages/app/src/pages/session/message-timeline.tsx
+++ b/packages/app/src/pages/session/message-timeline.tsx
@@ -1097,6 +1097,7 @@ export function MessageTimeline(props: {
                         active={active()}
                         status={active() ? sessionStatus() : undefined}
                         showReasoningSummaries={settings.general.showReasoningSummaries()}
+                        reasoningToolDefaultOpen={settings.general.reasoningToolDefaultOpen()}
                         shellToolDefaultOpen={settings.general.shellToolPartsExpanded()}
                         editToolDefaultOpen={settings.general.editToolPartsExpanded()}
                         classes={{
diff --git a/packages/app/src/pages/session/use-session-commands.tsx b/packages/app/src/pages/session/use-session-commands.tsx
index 2397953737c7..b82dea957b61 100644
--- a/packages/app/src/pages/session/use-session-commands.tsx
+++ b/packages/app/src/pages/session/use-session-commands.tsx
@@ -9,6 +9,7 @@ import { useLocal } from "@/context/local"
 import { usePermission } from "@/context/permission"
 import { usePrompt } from "@/context/prompt"
 import { useSDK } from "@/context/sdk"
+import { useSettings } from "@/context/settings"
 import { useSync } from "@/context/sync"
 import { useTerminal } from "@/context/terminal"
 import { showToast } from "@opencode-ai/ui/toast"
@@ -41,6 +42,7 @@ export const useSessionCommands = (actions: SessionCommandContext) => {
   const permission = usePermission()
   const prompt = usePrompt()
   const sdk = useSDK()
+  const settings = useSettings()
   const sync = useSync()
   const terminal = useTerminal()
   const layout = useLayout()
@@ -118,6 +120,7 @@ export const useSessionCommands = (actions: SessionCommandContext) => {
   const mcpCommand = withCategory(language.t("command.category.mcp"))
   const agentCommand = withCategory(language.t("command.category.agent"))
   const permissionsCommand = withCategory(language.t("command.category.permissions"))
+  const settingsCommand = withCategory(language.t("command.category.settings"))
 
   const isAutoAcceptActive = () => {
     const sessionID = params.id
@@ -559,6 +562,18 @@ export const useSessionCommands = (actions: SessionCommandContext) => {
     }),
   ]
 
+  const settingsCmds = () => [
+    settingsCommand({
+      id: "settings.thinking",
+      title: settings.general.reasoningToolDefaultOpen()
+        ? language.t("command.settings.thinking.disable")
+        : language.t("command.settings.thinking.enable"),
+      description: language.t("command.settings.thinking.description"),
+      slash: "thinking",
+      onSelect: () => settings.general.setReasoningToolDefaultOpen(!settings.general.reasoningToolDefaultOpen()),
+    }),
+  ]
+
   command.register("session", () => [
     ...sessionCmds(),
     ...shareCmds(),
@@ -571,5 +586,6 @@ export const useSessionCommands = (actions: SessionCommandContext) => {
     ...mcpCmds(),
     ...agentCmds(),
     ...permissionsCmds(),
+    ...settingsCmds(),
   ])
 }
diff --git a/packages/ui/src/components/message-part.tsx b/packages/ui/src/components/message-part.tsx
index 3627eca409ad..bcd319c40e7e 100644
--- a/packages/ui/src/components/message-part.tsx
+++ b/packages/ui/src/components/message-part.tsx
@@ -570,25 +570,27 @@ function index<T extends { id: string }>(items: readonly T[]) {
   return new Map(items.map((item) => [item.id, item] as const))
 }
 
-function renderable(part: PartType, showReasoningSummaries = true) {
+function renderable(part: PartType, showReasoningSummaries = false) {
   if (part.type === "tool") {
     if (HIDDEN_TOOLS.has(part.tool)) return false
     if (part.tool === "question") return part.state.status !== "pending" && part.state.status !== "running"
     return true
   }
   if (part.type === "text") return !!part.text?.trim()
-  if (part.type === "reasoning") return showReasoningSummaries && !!part.text?.trim()
+  if (part.type === "reasoning") return !!part.text?.trim()
   return !!PART_MAPPING[part.type]
 }
 
-function toolDefaultOpen(tool: string, shell = false, edit = false) {
+function toolDefaultOpen(tool: string, shell = false, edit = false, reasoning = false) {
   if (tool === "bash") return shell
   if (tool === "edit" || tool === "write" || tool === "apply_patch") return edit
+  if (tool === "reasoning") return reasoning
 }
 
-function partDefaultOpen(part: PartType, shell = false, edit = false) {
+function partDefaultOpen(part: PartType, shell = false, edit = false, reasoning = false) {
+  if (part.type === "reasoning") return reasoning
   if (part.type !== "tool") return
-  return toolDefaultOpen(part.tool, shell, edit)
+  return toolDefaultOpen(part.tool, shell, edit, reasoning)
 }
 
 export function AssistantParts(props: {
@@ -597,6 +599,7 @@ export function AssistantParts(props: {
   turnDurationMs?: number
   working?: boolean
   showReasoningSummaries?: boolean
+  reasoningToolDefaultOpen?: boolean
   shellToolDefaultOpen?: boolean
   editToolDefaultOpen?: boolean
 }) {
@@ -616,7 +619,7 @@ export function AssistantParts(props: {
       groupParts(
         props.messages.flatMap((message) =>
           list(data.store.part?.[message.id], emptyParts)
-            .filter((part) => renderable(part, props.showReasoningSummaries ?? true))
+            .filter((part) => renderable(part, props.showReasoningSummaries ?? false))
             .map((part) => ({
               messageID: message.id,
               part,
@@ -679,7 +682,12 @@ export function AssistantParts(props: {
                         message={message()!}
                         showAssistantCopyPartID={props.showAssistantCopyPartID}
                         turnDurationMs={props.turnDurationMs}
-                        defaultOpen={partDefaultOpen(item()!, props.shellToolDefaultOpen, props.editToolDefaultOpen)}
+                        defaultOpen={partDefaultOpen(
+                          item()!,
+                          props.shellToolDefaultOpen,
+                          props.editToolDefaultOpen,
+                          props.reasoningToolDefaultOpen,
+                        )}
                       />
                     </Show>
                   </Show>
@@ -831,7 +839,7 @@ export function AssistantMessageDisplay(props: {
     () =>
       groupParts(
         props.parts
-          .filter((part) => renderable(part, props.showReasoningSummaries ?? true))
+          .filter((part) => renderable(part, props.showReasoningSummaries ?? false))
           .map((part) => ({
             messageID: props.message.id,
             part,
@@ -1510,6 +1518,8 @@ PART_MAPPING["text"] = function TextPartDisplay(props) {
 }
 
 PART_MAPPING["reasoning"] = function ReasoningPartDisplay(props) {
+  const data = useData()
+  const i18n = useI18n()
   const part = () => props.part as ReasoningPart
   const streaming = createMemo(
     () => props.message.role === "assistant" && typeof (props.message as AssistantMessage).time.completed !== "number",
@@ -1518,11 +1528,29 @@ PART_MAPPING["reasoning"] = function ReasoningPartDisplay(props) {
 
   return (
     <Show when={text()}>
-      <div data-component="reasoning-part">
-        <Show when={streaming()} fallback={<Markdown text={text()} cacheKey={part().id} streaming={false} />}>
-          <PacedMarkdown text={text()} cacheKey={part().id} streaming={streaming()} />
-        </Show>
-      </div>
+      <Collapsible defaultOpen={props.defaultOpen} variant="ghost" class="tool-collapsible">
+        <Collapsible.Trigger>
+          <div data-component="reasoning-part-trigger" class="flex items-center gap-2 min-w-0">
+            <span
+              data-slot="reasoning-part-title"
+              class="min-w-0 flex items-center gap-2 text-14-medium text-text-strong"
+            >
+              <Icon name="brain" class="shrink-0" />
+              <span data-slot="reasoning-part-label" class="truncate">
+                {i18n.t("ui.messagePart.thinking")}
+              </span>
+            </span>
+            <Collapsible.Arrow />
+          </div>
+        </Collapsible.Trigger>
+        <Collapsible.Content>
+          <div data-component="reasoning-part" class="mt-2">
+            <Show when={streaming()} fallback={<Markdown text={text()} cacheKey={part().id} streaming={false} />}>
+              <PacedMarkdown text={text()} cacheKey={part().id} streaming={streaming()} />
+            </Show>
+          </div>
+        </Collapsible.Content>
+      </Collapsible>
     </Show>
   )
 }
diff --git a/packages/ui/src/components/session-turn.css b/packages/ui/src/components/session-turn.css
index b01343a01d7c..3bb9b12ad3df 100644
--- a/packages/ui/src/components/session-turn.css
+++ b/packages/ui/src/components/session-turn.css
@@ -43,32 +43,6 @@
     align-self: stretch;
   }
 
-  [data-slot="session-turn-thinking"] {
-    display: flex;
-    align-items: center;
-    gap: 8px;
-    width: 100%;
-    min-width: 0;
-    color: var(--text-weak);
-    font-family: var(--font-family-sans);
-    font-size: var(--font-size-base);
-    font-weight: var(--font-weight-medium);
-    line-height: 20px;
-    min-height: 20px;
-
-    [data-component="spinner"] {
-      width: 16px;
-      height: 16px;
-    }
-  }
-
-  [data-component="text-reveal"].session-turn-thinking-heading {
-    flex: 1 1 auto;
-    min-width: 0;
-    color: var(--text-weaker);
-    font-weight: var(--font-weight-regular);
-  }
-
   .error-card {
     color: var(--text-on-critical-base);
     max-height: 240px;
diff --git a/packages/ui/src/components/session-turn.tsx b/packages/ui/src/components/session-turn.tsx
index e891a6febe2f..729cef825e2b 100644
--- a/packages/ui/src/components/session-turn.tsx
+++ b/packages/ui/src/components/session-turn.tsx
@@ -100,7 +100,7 @@ function partState(part: PartType, showReasoningSummaries: boolean) {
   }
   if (part.type === "text") return part.text?.trim() ? ("visible" as const) : undefined
   if (part.type === "reasoning") {
-    if (showReasoningSummaries && part.text?.trim()) return "visible" as const
+    if (part.text?.trim()) return "visible" as const
     return
   }
   if (PART_MAPPING[part.type]) return "visible" as const
@@ -150,6 +150,7 @@ export function SessionTurn(
     messages?: MessageType[]
     actions?: UserActions
     showReasoningSummaries?: boolean
+    reasoningToolDefaultOpen?: boolean
     shellToolDefaultOpen?: boolean
     editToolDefaultOpen?: boolean
     active?: boolean
@@ -322,7 +323,8 @@ export function SessionTurn(
     return data.store.session_status[props.sessionID] ?? idle
   })
   const working = createMemo(() => status().type !== "idle" && active())
-  const showReasoningSummaries = createMemo(() => props.showReasoningSummaries ?? true)
+  const showReasoningSummaries = createMemo(() => props.showReasoningSummaries ?? false)
+  const reasoningDefaultOpen = createMemo(() => props.reasoningToolDefaultOpen ?? true)
 
   const assistantCopyPartID = createMemo(() => {
     if (working()) return null
@@ -361,13 +363,6 @@ export function SessionTurn(
     return { visible, reason }
   })
   const assistantVisible = createMemo(() => assistantDerived().visible)
-  const reasoningHeading = createMemo(() => assistantDerived().reason)
-  const showThinking = createMemo(() => {
-    if (!working() || !!error()) return false
-    if (status().type === "retry") return false
-    if (showReasoningSummaries()) return assistantVisible() === 0
-    return true
-  })
 
   const autoScroll = createAutoScroll({
     working,
@@ -407,24 +402,12 @@ export function SessionTurn(
                     turnDurationMs={turnDurationMs()}
                     working={working()}
                     showReasoningSummaries={showReasoningSummaries()}
+                    reasoningToolDefaultOpen={reasoningDefaultOpen()}
                     shellToolDefaultOpen={props.shellToolDefaultOpen}
                     editToolDefaultOpen={props.editToolDefaultOpen}
                   />
                 </div>
               </Show>
-              <Show when={showThinking()}>
-                <div data-slot="session-turn-thinking">
-                  <TextShimmer text={i18n.t("ui.sessionTurn.status.thinking")} />
-                  <Show when={!showReasoningSummaries()}>
-                    <TextReveal
-                      text={reasoningHeading()}
-                      class="session-turn-thinking-heading"
-                      travel={25}
-                      duration={700}
-                    />
-                  </Show>
-                </div>
-              </Show>
               <SessionRetry status={status()} show={active()} />
               <Show when={edited() > 0 && !working()}>
                 <div
diff --git a/packages/ui/src/i18n/ar.ts b/packages/ui/src/i18n/ar.ts
index ea4d03ac67ac..a7149994aafd 100644
--- a/packages/ui/src/i18n/ar.ts
+++ b/packages/ui/src/i18n/ar.ts
@@ -67,6 +67,7 @@ export const dict = {
   "ui.messagePart.context.search.other": "{{count}} عمليات بحث",
   "ui.messagePart.context.list.one": "{{count}} قائمة",
   "ui.messagePart.context.list.other": "{{count}} قوائم",
+  "ui.messagePart.thinking": "التفكير",
   "ui.messagePart.diagnostic.error": "خطأ",
   "ui.messagePart.title.edit": "تحرير",
   "ui.messagePart.title.write": "كتابة",
diff --git a/packages/ui/src/i18n/br.ts b/packages/ui/src/i18n/br.ts
index e8aefd937815..acbd585edd84 100644
--- a/packages/ui/src/i18n/br.ts
+++ b/packages/ui/src/i18n/br.ts
@@ -67,6 +67,7 @@ export const dict = {
   "ui.messagePart.context.search.other": "{{count}} pesquisas",
   "ui.messagePart.context.list.one": "{{count}} lista",
   "ui.messagePart.context.list.other": "{{count}} listas",
+  "ui.messagePart.thinking": "Pensando",
   "ui.messagePart.diagnostic.error": "Erro",
   "ui.messagePart.title.edit": "Editar",
   "ui.messagePart.title.write": "Escrever",
diff --git a/packages/ui/src/i18n/bs.ts b/packages/ui/src/i18n/bs.ts
index 4e8ce8042561..7969b042a9a3 100644
--- a/packages/ui/src/i18n/bs.ts
+++ b/packages/ui/src/i18n/bs.ts
@@ -71,6 +71,7 @@ export const dict = {
   "ui.messagePart.context.search.other": "{{count}} pretrage",
   "ui.messagePart.context.list.one": "{{count}} lista",
   "ui.messagePart.context.list.other": "{{count}} liste",
+  "ui.messagePart.thinking": "Razmišljanje",
   "ui.messagePart.diagnostic.error": "Greška",
   "ui.messagePart.title.edit": "Uredi",
   "ui.messagePart.title.write": "Napiši",
diff --git a/packages/ui/src/i18n/da.ts b/packages/ui/src/i18n/da.ts
index 846fb3ecaa27..6e59bd3c2f8c 100644
--- a/packages/ui/src/i18n/da.ts
+++ b/packages/ui/src/i18n/da.ts
@@ -66,6 +66,7 @@ export const dict = {
   "ui.messagePart.context.search.other": "{{count}} søgninger",
   "ui.messagePart.context.list.one": "{{count}} liste",
   "ui.messagePart.context.list.other": "{{count}} lister",
+  "ui.messagePart.thinking": "Tænkning",
   "ui.messagePart.diagnostic.error": "Fejl",
   "ui.messagePart.title.edit": "Rediger",
   "ui.messagePart.title.write": "Skriv",
diff --git a/packages/ui/src/i18n/de.ts b/packages/ui/src/i18n/de.ts
index c07ceade2f62..500d562627ca 100644
--- a/packages/ui/src/i18n/de.ts
+++ b/packages/ui/src/i18n/de.ts
@@ -72,6 +72,7 @@ export const dict = {
   "ui.messagePart.context.search.other": "{{count}} Suchen",
   "ui.messagePart.context.list.one": "{{count}} Liste",
   "ui.messagePart.context.list.other": "{{count}} Listen",
+  "ui.messagePart.thinking": "Denken",
   "ui.messagePart.diagnostic.error": "Fehler",
   "ui.messagePart.title.edit": "Bearbeiten",
   "ui.messagePart.title.write": "Schreiben",
diff --git a/packages/ui/src/i18n/en.ts b/packages/ui/src/i18n/en.ts
index 837fd5afcbcd..e07c1edb43e9 100644
--- a/packages/ui/src/i18n/en.ts
+++ b/packages/ui/src/i18n/en.ts
@@ -79,6 +79,7 @@ export const dict: Record<string, string> = {
   "ui.messagePart.context.search.other": "{{count}} searches",
   "ui.messagePart.context.list.one": "{{count}} list",
   "ui.messagePart.context.list.other": "{{count}} lists",
+  "ui.messagePart.thinking": "Thinking",
 
   "ui.list.loading": "Loading",
   "ui.list.empty": "No results",
diff --git a/packages/ui/src/i18n/es.ts b/packages/ui/src/i18n/es.ts
index 3f4475a39bd2..eb3688ec377f 100644
--- a/packages/ui/src/i18n/es.ts
+++ b/packages/ui/src/i18n/es.ts
@@ -67,6 +67,7 @@ export const dict = {
   "ui.messagePart.context.search.other": "{{count}} búsquedas",
   "ui.messagePart.context.list.one": "{{count}} lista",
   "ui.messagePart.context.list.other": "{{count}} listas",
+  "ui.messagePart.thinking": "Pensando",
   "ui.messagePart.diagnostic.error": "Error",
   "ui.messagePart.title.edit": "Editar",
   "ui.messagePart.title.write": "Escribir",
diff --git a/packages/ui/src/i18n/fr.ts b/packages/ui/src/i18n/fr.ts
index 9cf17d5e336b..caac68d797f3 100644
--- a/packages/ui/src/i18n/fr.ts
+++ b/packages/ui/src/i18n/fr.ts
@@ -67,6 +67,7 @@ export const dict = {
   "ui.messagePart.context.search.other": "{{count}} recherches",
   "ui.messagePart.context.list.one": "{{count}} liste",
   "ui.messagePart.context.list.other": "{{count}} listes",
+  "ui.messagePart.thinking": "Réflexion",
   "ui.messagePart.diagnostic.error": "Erreur",
   "ui.messagePart.title.edit": "Modifier",
   "ui.messagePart.title.write": "Écrire",
diff --git a/packages/ui/src/i18n/ja.ts b/packages/ui/src/i18n/ja.ts
index 5bb7f1376bd3..ba6b62bda519 100644
--- a/packages/ui/src/i18n/ja.ts
+++ b/packages/ui/src/i18n/ja.ts
@@ -66,6 +66,7 @@ export const dict = {
   "ui.messagePart.context.search.other": "{{count}} 件の検索",
   "ui.messagePart.context.list.one": "{{count}} 件のリスト",
   "ui.messagePart.context.list.other": "{{count}} 件のリスト",
+  "ui.messagePart.thinking": "思考中",
   "ui.messagePart.diagnostic.error": "エラー",
   "ui.messagePart.title.edit": "編集",
   "ui.messagePart.title.write": "作成",
diff --git a/packages/ui/src/i18n/ko.ts b/packages/ui/src/i18n/ko.ts
index 088a2865af4a..3ddea0c8397d 100644
--- a/packages/ui/src/i18n/ko.ts
+++ b/packages/ui/src/i18n/ko.ts
@@ -67,6 +67,7 @@ export const dict = {
   "ui.messagePart.context.search.other": "{{count}}개 검색",
   "ui.messagePart.context.list.one": "{{count}}개 목록",
   "ui.messagePart.context.list.other": "{{count}}개 목록",
+  "ui.messagePart.thinking": "생각 중",
   "ui.messagePart.diagnostic.error": "오류",
   "ui.messagePart.title.edit": "편집",
   "ui.messagePart.title.write": "작성",
diff --git a/packages/ui/src/i18n/no.ts b/packages/ui/src/i18n/no.ts
index af6e399eac5f..4c545d126a7b 100644
--- a/packages/ui/src/i18n/no.ts
+++ b/packages/ui/src/i18n/no.ts
@@ -70,6 +70,7 @@ export const dict: Record<Keys, string> = {
   "ui.messagePart.context.search.other": "{{count}} søk",
   "ui.messagePart.context.list.one": "{{count}} liste",
   "ui.messagePart.context.list.other": "{{count}} lister",
+  "ui.messagePart.thinking": "Tenker",
   "ui.messagePart.diagnostic.error": "Feil",
   "ui.messagePart.title.edit": "Rediger",
   "ui.messagePart.title.write": "Skriv",
diff --git a/packages/ui/src/i18n/pl.ts b/packages/ui/src/i18n/pl.ts
index 2385edfeb751..ed70395b13be 100644
--- a/packages/ui/src/i18n/pl.ts
+++ b/packages/ui/src/i18n/pl.ts
@@ -66,6 +66,7 @@ export const dict = {
   "ui.messagePart.context.search.other": "{{count}} wyszukiwania",
   "ui.messagePart.context.list.one": "{{count}} lista",
   "ui.messagePart.context.list.other": "{{count}} listy",
+  "ui.messagePart.thinking": "Myślenie",
   "ui.messagePart.diagnostic.error": "Błąd",
   "ui.messagePart.title.edit": "Edycja",
   "ui.messagePart.title.write": "Pisanie",
diff --git a/packages/ui/src/i18n/ru.ts b/packages/ui/src/i18n/ru.ts
index f78bd5c14b60..bc75c80581bf 100644
--- a/packages/ui/src/i18n/ru.ts
+++ b/packages/ui/src/i18n/ru.ts
@@ -66,6 +66,7 @@ export const dict = {
   "ui.messagePart.context.search.other": "{{count}} поисков",
   "ui.messagePart.context.list.one": "{{count}} список",
   "ui.messagePart.context.list.other": "{{count}} списков",
+  "ui.messagePart.thinking": "Размышление",
   "ui.messagePart.diagnostic.error": "Ошибка",
   "ui.messagePart.title.edit": "Редактировать",
   "ui.messagePart.title.write": "Написать",
diff --git a/packages/ui/src/i18n/th.ts b/packages/ui/src/i18n/th.ts
index a49fc2e52e28..d94f60e24a40 100644
--- a/packages/ui/src/i18n/th.ts
+++ b/packages/ui/src/i18n/th.ts
@@ -68,6 +68,7 @@ export const dict = {
   "ui.messagePart.context.search.other": "ค้นหา {{count}} รายการ",
   "ui.messagePart.context.list.one": "รายการ {{count}} รายการ",
   "ui.messagePart.context.list.other": "รายการ {{count}} รายการ",
+  "ui.messagePart.thinking": "กำลังคิด",
   "ui.messagePart.diagnostic.error": "ข้อผิดพลาด",
   "ui.messagePart.title.edit": "แก้ไข",
   "ui.messagePart.title.write": "เขียน",
diff --git a/packages/ui/src/i18n/tr.ts b/packages/ui/src/i18n/tr.ts
index e6b50c1c09a3..c539d3a8727e 100644
--- a/packages/ui/src/i18n/tr.ts
+++ b/packages/ui/src/i18n/tr.ts
@@ -73,6 +73,7 @@ export const dict = {
   "ui.messagePart.context.search.other": "{{count}} arama",
   "ui.messagePart.context.list.one": "{{count}} liste",
   "ui.messagePart.context.list.other": "{{count}} liste",
+  "ui.messagePart.thinking": "Düşünüyor",
   "ui.messagePart.diagnostic.error": "Hata",
   "ui.messagePart.title.edit": "Düzenle",
   "ui.messagePart.title.write": "Yaz",
diff --git a/packages/ui/src/i18n/zh.ts b/packages/ui/src/i18n/zh.ts
index 5779754376b9..384667c3af96 100644
--- a/packages/ui/src/i18n/zh.ts
+++ b/packages/ui/src/i18n/zh.ts
@@ -71,6 +71,7 @@ export const dict = {
   "ui.messagePart.context.search.other": "{{count}} 次搜索",
   "ui.messagePart.context.list.one": "{{count}} 个列表",
   "ui.messagePart.context.list.other": "{{count}} 个列表",
+  "ui.messagePart.thinking": "思考中",
   "ui.messagePart.diagnostic.error": "错误",
   "ui.messagePart.title.edit": "编辑",
   "ui.messagePart.title.write": "写入",
diff --git a/packages/ui/src/i18n/zht.ts b/packages/ui/src/i18n/zht.ts
index 2d433b57ab41..09189a13ee85 100644
--- a/packages/ui/src/i18n/zht.ts
+++ b/packages/ui/src/i18n/zht.ts
@@ -71,6 +71,7 @@ export const dict = {
   "ui.messagePart.context.search.other": "{{count}} 次搜尋",
   "ui.messagePart.context.list.one": "{{count}} 個清單",
   "ui.messagePart.context.list.other": "{{count}} 個清單",
+  "ui.messagePart.thinking": "思考中",
   "ui.messagePart.diagnostic.error": "錯誤",
   "ui.messagePart.title.edit": "編輯",
   "ui.messagePart.title.write": "寫入",