diff --git a/CHANGELOG.md b/CHANGELOG.md
index f3c541684ea..1c1eab9ba8b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -36,6 +36,7 @@ Docs: https://docs.openclaw.ai
 
 ### Fixes
 
+- Control UI/chat: add a per-session thinking-level picker in the chat header and mobile chat settings, and keep the browser bundle on UI-local thinking/session-key helpers so Safari no longer crashes on Node-only imports before rendering chat controls.
 - Synology Chat/security: route webhook token comparison through the shared constant-time secret helper for consistency with other bundled plugins.
 - Gateway/security: scope loopback browser-origin auth throttling by normalized origin so one localhost Control UI tab cannot lock out a different localhost browser origin after repeated auth failures.
 - Node exec approvals: keep node-host `system.run` approvals bound to the prepared execution plan, so script-drift revalidation still runs after agent-side approval forwarding.
diff --git a/ui/src/styles/chat/layout.css b/ui/src/styles/chat/layout.css
index 99bf65644bb..9455ee13495 100644
--- a/ui/src/styles/chat/layout.css
+++ b/ui/src/styles/chat/layout.css
@@ -743,8 +743,8 @@
 }
 
 .chat-controls__session {
-  min-width: 140px;
-  max-width: 300px;
+  min-width: 98px;
+  max-width: 190px;
 }
 
 .chat-controls__session-row {
@@ -755,8 +755,13 @@
 }
 
 .chat-controls__model {
-  min-width: 170px;
-  max-width: 320px;
+  min-width: 124px;
+  max-width: 206px;
+}
+
+.chat-controls__thinking-select {
+  min-width: 88px;
+  max-width: 118px;
 }
 
 .chat-controls__thinking {
@@ -781,13 +786,17 @@
 .chat-controls__session select {
   padding: 6px 10px;
   font-size: 13px;
-  max-width: 300px;
+  max-width: 190px;
   overflow: hidden;
   text-overflow: ellipsis;
 }
 
 .chat-controls__model select {
-  max-width: 320px;
+  max-width: 206px;
+}
+
+.chat-controls__thinking-select select {
+  max-width: 118px;
 }
 
 .chat-controls__thinking {
@@ -818,6 +827,11 @@
     max-width: none;
   }
 
+  .chat-controls__thinking-select {
+    min-width: 130px;
+    max-width: none;
+  }
+
   .chat-controls {
     gap: 8px;
   }
@@ -863,6 +877,10 @@
   .chat-controls__model {
     min-width: 150px;
   }
+
+  .chat-controls__thinking-select {
+    min-width: 140px;
+  }
 }
 
 /* Chat loading skeleton */
diff --git a/ui/src/ui/app-chat.ts b/ui/src/ui/app-chat.ts
index 637ba709236..9ace7542120 100644
--- a/ui/src/ui/app-chat.ts
+++ b/ui/src/ui/app-chat.ts
@@ -1,4 +1,3 @@
-import { parseAgentSessionKey } from "../../../src/sessions/session-key-utils.js";
 import { scheduleChatScroll, resetChatScroll } from "./app-scroll.ts";
 import { setLastActiveSessionKey } from "./app-settings.ts";
 import { resetToolStream } from "./app-tool-stream.ts";
@@ -10,6 +9,7 @@ import { loadModels } from "./controllers/models.ts";
 import { loadSessions } from "./controllers/sessions.ts";
 import type { GatewayBrowserClient, GatewayHelloOk } from "./gateway.ts";
 import { normalizeBasePath } from "./navigation.ts";
+import { parseAgentSessionKey } from "./session-key.ts";
 import type { ChatModelOverride, ModelCatalogEntry } from "./types.ts";
 import type { SessionsListResult } from "./types.ts";
 import type { ChatAttachment, ChatQueueItem } from "./ui-types.ts";
diff --git a/ui/src/ui/app-render.helpers.ts b/ui/src/ui/app-render.helpers.ts
index e85913dd46d..8a66aa4c2a1 100644
--- a/ui/src/ui/app-render.helpers.ts
+++ b/ui/src/ui/app-render.helpers.ts
@@ -1,6 +1,5 @@
 import { html, nothing } from "lit";
 import { repeat } from "lit/directives/repeat.js";
-import { parseAgentSessionKey } from "../../../src/sessions/session-key-utils.js";
 import { t } from "../i18n/index.ts";
 import { refreshChat } from "./app-chat.ts";
 import { syncUrlWithSessionKey } from "./app-settings.ts";
@@ -16,8 +15,14 @@ import { ChatState, loadChatHistory } from "./controllers/chat.ts";
 import { loadSessions } from "./controllers/sessions.ts";
 import { icons } from "./icons.ts";
 import { iconForTab, pathForTab, titleForTab, type Tab } from "./navigation.ts";
+import { parseAgentSessionKey } from "./session-key.ts";
 import type { ThemeTransitionContext } from "./theme-transition.ts";
 import type { ThemeMode, ThemeName } from "./theme.ts";
+import {
+  listThinkingLevelLabels,
+  normalizeThinkLevel,
+  resolveThinkingDefaultForModel,
+} from "./thinking.ts";
 import type { SessionsListResult } from "./types.ts";
 
 type SessionDefaultsSnapshot = {
@@ -133,11 +138,16 @@ function renderCronFilterIcon(hiddenCount: number) {
 export function renderChatSessionSelect(state: AppViewState) {
   const sessionGroups = resolveSessionOptionGroups(state, state.sessionKey, state.sessionsResult);
   const modelSelect = renderChatModelSelect(state);
+  const thinkingSelect = renderChatThinkingSelect(state);
+  const selectedSessionLabel =
+    sessionGroups.flatMap((group) => group.options).find((entry) => entry.key === state.sessionKey)
+      ?.label ?? state.sessionKey;
   return html`
     <div class="chat-controls__session-row">
       <label class="field chat-controls__session">
         <select
           .value=${state.sessionKey}
+          title=${selectedSessionLabel}
           ?disabled=${!state.connected || sessionGroups.length === 0}
           @change=${(e: Event) => {
             const next = (e.target as HTMLSelectElement).value;
@@ -162,7 +172,7 @@ export function renderChatSessionSelect(state: AppViewState) {
           )}
         </select>
       </label>
-      ${modelSelect}
+      ${modelSelect} ${thinkingSelect}
     </div>
   `;
 }
@@ -436,6 +446,7 @@ export function renderChatMobileToggle(state: AppViewState) {
               )}
             </select>
           </label>
+          ${renderChatThinkingSelect(state)}
           <div class="chat-controls__thinking">
             <button
               class="btn btn--sm btn--icon ${showThinking ? "active" : ""}"
@@ -532,11 +543,16 @@ function renderChatModelSelect(state: AppViewState) {
     state.chatLoading || state.chatSending || Boolean(state.chatRunId) || state.chatStream !== null;
   const disabled =
     !state.connected || busy || (state.chatModelsLoading && options.length === 0) || !state.client;
+  const selectedLabel =
+    currentOverride === ""
+      ? defaultLabel
+      : (options.find((entry) => entry.value === currentOverride)?.label ?? currentOverride);
   return html`
     <label class="field chat-controls__session chat-controls__model">
       <select
         data-chat-model-select="true"
         aria-label="Chat model"
+        title=${selectedLabel}
         ?disabled=${disabled}
         @change=${async (e: Event) => {
           const next = (e.target as HTMLSelectElement).value.trim();
@@ -557,6 +573,125 @@ function renderChatModelSelect(state: AppViewState) {
   `;
 }
 
+type ChatThinkingSelectOption = {
+  value: string;
+  label: string;
+};
+
+type ChatThinkingSelectState = {
+  currentOverride: string;
+  defaultLabel: string;
+  options: ChatThinkingSelectOption[];
+};
+
+function resolveThinkingTargetModel(state: AppViewState): {
+  provider: string | null;
+  model: string | null;
+} {
+  const activeRow = state.sessionsResult?.sessions?.find((row) => row.key === state.sessionKey);
+  return {
+    provider: activeRow?.modelProvider ?? state.sessionsResult?.defaults?.modelProvider ?? null,
+    model: activeRow?.model ?? state.sessionsResult?.defaults?.model ?? null,
+  };
+}
+
+function buildThinkingOptions(
+  provider: string | null,
+  model: string | null,
+  currentOverride: string,
+): ChatThinkingSelectOption[] {
+  const seen = new Set<string>();
+  const options: ChatThinkingSelectOption[] = [];
+
+  const addOption = (value: string, label?: string) => {
+    const trimmed = value.trim();
+    if (!trimmed) {
+      return;
+    }
+    const key = trimmed.toLowerCase();
+    if (seen.has(key)) {
+      return;
+    }
+    seen.add(key);
+    options.push({
+      value: trimmed,
+      label:
+        label ??
+        trimmed
+          .split(/[-_]/g)
+          .map((part) => (part ? part[0].toUpperCase() + part.slice(1) : part))
+          .join(" "),
+    });
+  };
+
+  for (const label of listThinkingLevelLabels(provider)) {
+    const normalized = normalizeThinkLevel(label) ?? label.trim().toLowerCase();
+    addOption(normalized);
+  }
+  if (currentOverride) {
+    addOption(currentOverride);
+  }
+  return options;
+}
+
+function resolveChatThinkingSelectState(state: AppViewState): ChatThinkingSelectState {
+  const activeRow = state.sessionsResult?.sessions?.find((row) => row.key === state.sessionKey);
+  const persisted = activeRow?.thinkingLevel;
+  const currentOverride =
+    typeof persisted === "string" && persisted.trim()
+      ? (normalizeThinkLevel(persisted) ?? persisted.trim())
+      : "";
+  const { provider, model } = resolveThinkingTargetModel(state);
+  const defaultLevel =
+    provider && model
+      ? resolveThinkingDefaultForModel({
+          provider,
+          model,
+          catalog: state.chatModelCatalog ?? [],
+        })
+      : "off";
+  return {
+    currentOverride,
+    defaultLabel: `Default (${defaultLevel})`,
+    options: buildThinkingOptions(provider, model, currentOverride),
+  };
+}
+
+function renderChatThinkingSelect(state: AppViewState) {
+  const { currentOverride, defaultLabel, options } = resolveChatThinkingSelectState(state);
+  const busy =
+    state.chatLoading || state.chatSending || Boolean(state.chatRunId) || state.chatStream !== null;
+  const disabled = !state.connected || busy || !state.client;
+  const selectedLabel =
+    currentOverride === ""
+      ? defaultLabel
+      : (options.find((entry) => entry.value === currentOverride)?.label ?? currentOverride);
+  return html`
+    <label class="field chat-controls__session chat-controls__thinking-select">
+      <select
+        data-chat-thinking-select="true"
+        aria-label="Chat thinking level"
+        title=${selectedLabel}
+        ?disabled=${disabled}
+        @change=${async (e: Event) => {
+          const next = (e.target as HTMLSelectElement).value.trim();
+          await switchChatThinkingLevel(state, next);
+        }}
+      >
+        <option value="" ?selected=${currentOverride === ""}>${defaultLabel}</option>
+        ${repeat(
+          options,
+          (entry) => entry.value,
+          (entry) =>
+            html`<option value=${entry.value} ?selected=${entry.value === currentOverride}>
+              ${entry.label}
+            </option>`,
+        )}
+      </select>
+    </label>
+  `;
+}
+
 async function switchChatModel(state: AppViewState, nextModel: string) {
   if (!state.client || !state.connected) {
     return;
@@ -587,6 +722,60 @@ async function switchChatModel(state: AppViewState, nextModel: string) {
   }
 }
 
+function patchSessionThinkingLevel(
+  state: AppViewState,
+  sessionKey: string,
+  thinkingLevel: string | undefined,
+) {
+  const current = state.sessionsResult;
+  if (!current) {
+    return;
+  }
+  state.sessionsResult = {
+    ...current,
+    sessions: current.sessions.map((row) =>
+      row.key === sessionKey
+        ? {
+            ...row,
+            thinkingLevel,
+          }
+        : row,
+    ),
+  };
+}
+
+async function switchChatThinkingLevel(state: AppViewState, nextThinkingLevel: string) {
+  if (!state.client || !state.connected) {
+    return;
+  }
+  const targetSessionKey = state.sessionKey;
+  const activeRow = state.sessionsResult?.sessions?.find((row) => row.key === targetSessionKey);
+  const previousThinkingLevel = activeRow?.thinkingLevel;
+  const normalizedNext =
+    (normalizeThinkLevel(nextThinkingLevel) ?? nextThinkingLevel.trim()) || undefined;
+  const normalizedPrev =
+    typeof previousThinkingLevel === "string" && previousThinkingLevel.trim()
+      ? (normalizeThinkLevel(previousThinkingLevel) ?? previousThinkingLevel.trim())
+      : undefined;
+  if ((normalizedPrev ?? "") === (normalizedNext ?? "")) {
+    return;
+  }
+  state.lastError = null;
+  patchSessionThinkingLevel(state, targetSessionKey, normalizedNext);
+  state.chatThinkingLevel = normalizedNext ?? null;
+  try {
+    await state.client.request("sessions.patch", {
+      key: targetSessionKey,
+      thinkingLevel: normalizedNext ?? null,
+    });
+    await refreshSessionOptions(state);
+  } catch (err) {
+    patchSessionThinkingLevel(state, targetSessionKey, previousThinkingLevel);
+    state.chatThinkingLevel = normalizedPrev ?? null;
+    state.lastError = `Failed to set thinking level: ${String(err)}`;
+  }
+}
+
 /* ── Channel display labels ────────────────────────────── */
 const CHANNEL_LABELS: Record<string, string> = {
   bluebubbles: "iMessage",
diff --git a/ui/src/ui/app-render.ts b/ui/src/ui/app-render.ts
index 09231d86a30..87d44f88b3b 100644
--- a/ui/src/ui/app-render.ts
+++ b/ui/src/ui/app-render.ts
@@ -1,9 +1,4 @@
 import { html, nothing } from "lit";
-import {
-  buildAgentMainSessionKey,
-  parseAgentSessionKey,
-  resolveAgentIdFromSessionKey,
-} from "../../../src/routing/session-key.js";
 import { t } from "../i18n/index.ts";
 import { getSafeLocalStorage } from "../local-storage.ts";
 import { refreshChatAvatar } from "./app-chat.ts";
@@ -96,10 +91,15 @@ import {
   updateSkillEdit,
   updateSkillEnabled,
 } from "./controllers/skills.ts";
-import "./components/dashboard-header.ts";
 import { buildExternalLinkRel, EXTERNAL_LINK_TARGET } from "./external-link.ts";
+import "./components/dashboard-header.ts";
 import { icons } from "./icons.ts";
 import { normalizeBasePath, TAB_GROUPS, subtitleForTab, titleForTab } from "./navigation.ts";
+import {
+  buildAgentMainSessionKey,
+  parseAgentSessionKey,
+  resolveAgentIdFromSessionKey,
+} from "./session-key.ts";
 import { agentLogoUrl } from "./views/agents-utils.ts";
 import {
   resolveAgentConfig,
diff --git a/ui/src/ui/app.ts b/ui/src/ui/app.ts
index 4638bfa2ab3..74123bb0909 100644
--- a/ui/src/ui/app.ts
+++ b/ui/src/ui/app.ts
@@ -1,6 +1,5 @@
 import { LitElement } from "lit";
 import { customElement, state } from "lit/decorators.js";
-import { resolveAgentIdFromSessionKey } from "../../../src/routing/session-key.js";
 import { i18n, I18nController, isSupportedLocale } from "../i18n/index.ts";
 import {
   handleChannelConfigReload as handleChannelConfigReloadInternal,
@@ -71,6 +70,7 @@ import type {
 } from "./controllers/skills.ts";
 import type { GatewayBrowserClient, GatewayHelloOk } from "./gateway.ts";
 import type { Tab } from "./navigation.ts";
+import { resolveAgentIdFromSessionKey } from "./session-key.ts";
 import { loadSettings, type UiSettings } from "./storage.ts";
 import { VALID_THEME_NAMES, type ResolvedTheme, type ThemeMode, type ThemeName } from "./theme.ts";
 import type {
diff --git a/ui/src/ui/chat/slash-command-executor.ts b/ui/src/ui/chat/slash-command-executor.ts
index a426a527258..49f13614f6f 100644
--- a/ui/src/ui/chat/slash-command-executor.ts
+++ b/ui/src/ui/chat/slash-command-executor.ts
@@ -3,20 +3,19 @@
  * Calls gateway RPC methods and returns formatted results.
  */
 
-import {
-  formatThinkingLevels,
-  normalizeThinkLevel,
-  normalizeVerboseLevel,
-  resolveThinkingDefaultForModel,
-} from "../../../../src/auto-reply/thinking.shared.js";
+import { createChatModelOverride, resolvePreferredServerChatModel } from "../chat-model-ref.ts";
+import type { GatewayBrowserClient } from "../gateway.ts";
 import {
   DEFAULT_AGENT_ID,
   DEFAULT_MAIN_KEY,
   isSubagentSessionKey,
   parseAgentSessionKey,
-} from "../../../../src/routing/session-key.js";
-import { createChatModelOverride, resolvePreferredServerChatModel } from "../chat-model-ref.ts";
-import type { GatewayBrowserClient } from "../gateway.ts";
+} from "../session-key.ts";
+import {
+  formatThinkingLevels,
+  normalizeThinkLevel,
+  resolveThinkingDefaultForModel,
+} from "../thinking.ts";
 import type {
   AgentsListResult,
   ChatModelOverride,
@@ -56,6 +55,24 @@ export type SlashCommandContext = {
   modelCatalog?: ModelCatalogEntry[];
   sessionsResult?: SessionsListResult | null;
 };
+
+function normalizeVerboseLevel(raw?: string | null): "off" | "on" | "full" | undefined {
+  if (!raw) {
+    return undefined;
+  }
+  const key = raw.toLowerCase();
+  if (["off", "false", "no", "0"].includes(key)) {
+    return "off";
+  }
+  if (["full", "all", "everything"].includes(key)) {
+    return "full";
+  }
+  if (["on", "minimal", "true", "yes", "1"].includes(key)) {
+    return "on";
+  }
+  return undefined;
+}
+
 export async function executeSlashCommand(
   client: GatewayBrowserClient,
   sessionKey: string,
@@ -205,7 +222,7 @@ async function executeThink(
       return {
         content: formatDirectiveOptions(
           `Current thinking level: ${resolveCurrentThinkingLevel(session, models)}.`,
-          formatThinkingLevels(session?.modelProvider, session?.model),
+          formatThinkingLevels(session?.modelProvider),
         ),
       };
     } catch (err) {
@@ -218,7 +235,7 @@ async function executeThink(
     try {
       const session = await loadCurrentSession(client, sessionKey);
       return {
-        content: `Unrecognized thinking level "${rawLevel}". Valid levels: ${formatThinkingLevels(session?.modelProvider, session?.model)}.`,
+        content: `Unrecognized thinking level "${rawLevel}". Valid levels: ${formatThinkingLevels(session?.modelProvider)}.`,
       };
     } catch (err) {
       return { content: `Failed to validate thinking level: ${String(err)}` };
diff --git a/ui/src/ui/controllers/agents.ts b/ui/src/ui/controllers/agents.ts
index 625ccaa47f6..8a26de4dfe1 100644
--- a/ui/src/ui/controllers/agents.ts
+++ b/ui/src/ui/controllers/agents.ts
@@ -1,9 +1,9 @@
-import { resolveAgentIdFromSessionKey } from "../../../../src/routing/session-key.js";
 import {
   resolveChatModelOverride,
   resolvePreferredServerChatModelValue,
 } from "../chat-model-ref.ts";
 import type { GatewayBrowserClient } from "../gateway.ts";
+import { resolveAgentIdFromSessionKey } from "../session-key.ts";
 import type {
   AgentsListResult,
   ChatModelOverride,
diff --git a/ui/src/ui/session-key.ts b/ui/src/ui/session-key.ts
new file mode 100644
index 00000000000..44bdb79343b
--- /dev/null
+++ b/ui/src/ui/session-key.ts
@@ -0,0 +1,80 @@
+export type ParsedAgentSessionKey = {
+  agentId: string;
+  rest: string;
+};
+
+export const DEFAULT_AGENT_ID = "main";
+export const DEFAULT_MAIN_KEY = "main";
+
+const VALID_ID_RE = /^[a-z0-9][a-z0-9_-]{0,63}$/i;
+const INVALID_CHARS_RE = /[^a-z0-9_-]+/g;
+const LEADING_DASH_RE = /^-+/;
+const TRAILING_DASH_RE = /-+$/;
+
+export function parseAgentSessionKey(
+  sessionKey: string | undefined | null,
+): ParsedAgentSessionKey | null {
+  const raw = (sessionKey ?? "").trim().toLowerCase();
+  if (!raw) {
+    return null;
+  }
+  const parts = raw.split(":").filter(Boolean);
+  if (parts.length < 3 || parts[0] !== "agent") {
+    return null;
+  }
+  const agentId = parts[1]?.trim();
+  const rest = parts.slice(2).join(":");
+  if (!agentId || !rest) {
+    return null;
+  }
+  return { agentId, rest };
+}
+
+export function normalizeMainKey(value: string | undefined | null): string {
+  const trimmed = (value ?? "").trim();
+  return trimmed ? trimmed.toLowerCase() : DEFAULT_MAIN_KEY;
+}
+
+export function normalizeAgentId(value: string | undefined | null): string {
+  const trimmed = (value ?? "").trim();
+  if (!trimmed) {
+    return DEFAULT_AGENT_ID;
+  }
+  if (VALID_ID_RE.test(trimmed)) {
+    return trimmed.toLowerCase();
+  }
+  return (
+    trimmed
+      .toLowerCase()
+      .replace(INVALID_CHARS_RE, "-")
+      .replace(LEADING_DASH_RE, "")
+      .replace(TRAILING_DASH_RE, "")
+      .slice(0, 64) || DEFAULT_AGENT_ID
+  );
+}
+
+export function buildAgentMainSessionKey(params: {
+  agentId: string;
+  mainKey?: string | undefined;
+}): string {
+  const agentId = normalizeAgentId(params.agentId);
+  const mainKey = normalizeMainKey(params.mainKey);
+  return `agent:${agentId}:${mainKey}`;
+}
+
+export function resolveAgentIdFromSessionKey(sessionKey: string | undefined | null): string {
+  const parsed = parseAgentSessionKey(sessionKey);
+  return normalizeAgentId(parsed?.agentId ?? DEFAULT_AGENT_ID);
+}
+
+export function isSubagentSessionKey(sessionKey: string | undefined | null): boolean {
+  const raw = (sessionKey ?? "").trim();
+  if (!raw) {
+    return false;
+  }
+  if (raw.toLowerCase().startsWith("subagent:")) {
+    return true;
+  }
+  const parsed = parseAgentSessionKey(raw);
+  return Boolean((parsed?.rest ?? "").toLowerCase().startsWith("subagent:"));
+}
diff --git a/ui/src/ui/thinking.ts b/ui/src/ui/thinking.ts
new file mode 100644
index 00000000000..3aa12a5a55b
--- /dev/null
+++ b/ui/src/ui/thinking.ts
@@ -0,0 +1,93 @@
+export type ThinkingCatalogEntry = {
+  provider: string;
+  id: string;
+  reasoning?: boolean;
+};
+
+const BASE_THINKING_LEVELS = ["off", "minimal", "low", "medium", "high", "adaptive"] as const;
+const BINARY_THINKING_LEVELS = ["off", "on"] as const;
+const ANTHROPIC_CLAUDE_46_MODEL_RE = /^claude-(?:opus|sonnet)-4(?:\.|-)6(?:$|[-.])/i;
+const AMAZON_BEDROCK_CLAUDE_46_MODEL_RE = /claude-(?:opus|sonnet)-4(?:\.|-)6(?:$|[-.])/i;
+
+export function normalizeThinkingProviderId(provider?: string | null): string {
+  if (!provider) {
+    return "";
+  }
+  const normalized = provider.trim().toLowerCase();
+  if (normalized === "z.ai" || normalized === "z-ai") {
+    return "zai";
+  }
+  if (normalized === "bedrock" || normalized === "aws-bedrock") {
+    return "amazon-bedrock";
+  }
+  return normalized;
+}
+
+export function isBinaryThinkingProvider(provider?: string | null): boolean {
+  return normalizeThinkingProviderId(provider) === "zai";
+}
+
+export function normalizeThinkLevel(raw?: string | null): string | undefined {
+  if (!raw) {
+    return undefined;
+  }
+  const key = raw.trim().toLowerCase();
+  const collapsed = key.replace(/[\s_-]+/g, "");
+  if (collapsed === "adaptive" || collapsed === "auto") {
+    return "adaptive";
+  }
+  if (collapsed === "xhigh" || collapsed === "extrahigh") {
+    return "xhigh";
+  }
+  if (key === "off") {
+    return "off";
+  }
+  if (["on", "enable", "enabled"].includes(key)) {
+    return "low";
+  }
+  if (["min", "minimal"].includes(key)) {
+    return "minimal";
+  }
+  if (["low", "thinkhard", "think-hard", "think_hard"].includes(key)) {
+    return "low";
+  }
+  if (["mid", "med", "medium", "thinkharder", "think-harder", "harder"].includes(key)) {
+    return "medium";
+  }
+  if (
+    ["high", "ultra", "ultrathink", "think-hard", "thinkhardest", "highest", "max"].includes(key)
+  ) {
+    return "high";
+  }
+  if (key === "think") {
+    return "minimal";
+  }
+  return undefined;
+}
+
+export function listThinkingLevelLabels(provider?: string | null): readonly string[] {
+  return isBinaryThinkingProvider(provider) ? BINARY_THINKING_LEVELS : BASE_THINKING_LEVELS;
+}
+
+export function formatThinkingLevels(provider?: string | null): string {
+  return listThinkingLevelLabels(provider).join(", ");
+}
+
+export function resolveThinkingDefaultForModel(params: {
+  provider: string;
+  model: string;
+  catalog?: ThinkingCatalogEntry[];
+}): string {
+  const normalizedProvider = normalizeThinkingProviderId(params.provider);
+  const modelId = params.model.trim();
+  if (normalizedProvider === "anthropic" && ANTHROPIC_CLAUDE_46_MODEL_RE.test(modelId)) {
+    return "adaptive";
+  }
+  if (normalizedProvider === "amazon-bedrock" && AMAZON_BEDROCK_CLAUDE_46_MODEL_RE.test(modelId)) {
+    return "adaptive";
+  }
+  const candidate = params.catalog?.find(
+    (entry) => entry.provider === params.provider && entry.id === params.model,
+  );
+  return candidate?.reasoning ? "low" : "off";
+}
diff --git a/ui/src/ui/views/chat.test.ts b/ui/src/ui/views/chat.test.ts
index beea4022893..4705574c106 100644
--- a/ui/src/ui/views/chat.test.ts
+++ b/ui/src/ui/views/chat.test.ts
@@ -61,17 +61,23 @@ function createChatHeaderState(
   overrides: {
     model?: string | null;
     modelProvider?: string | null;
+    thinkingLevel?: string | null;
     models?: ModelCatalogEntry[];
     omitSessionFromList?: boolean;
   } = {},
 ): { state: AppViewState; request: ReturnType<typeof vi.fn> } {
   let currentModel = overrides.model ?? null;
   let currentModelProvider = overrides.modelProvider ?? (currentModel ? "openai" : null);
+  let currentThinkingLevel = overrides.thinkingLevel ?? null;
   const omitSessionFromList = overrides.omitSessionFromList ?? false;
   const catalog = overrides.models ?? createModelCatalog(...DEFAULT_CHAT_MODEL_CATALOG);
   const request = vi.fn(async (method: string, params: Record<string, unknown>) => {
     if (method === "sessions.patch") {
       const nextModel = (params.model as string | null | undefined) ?? null;
+      const nextThinkingLevel = params.thinkingLevel as string | null | undefined;
+      if ("thinkingLevel" in params) {
+        currentThinkingLevel = nextThinkingLevel ?? null;
+      }
       if (!nextModel) {
         currentModel = null;
         currentModelProvider = null;
@@ -97,11 +103,15 @@ function createChatHeaderState(
       return { messages: [], thinkingLevel: null };
     }
     if (method === "sessions.list") {
-      return createSessionsListResult({
+      const result = createSessionsListResult({
         model: currentModel,
         modelProvider: currentModelProvider,
         omitSessionFromList,
       });
+      if (result.sessions[0]) {
+        result.sessions[0].thinkingLevel = currentThinkingLevel ?? undefined;
+      }
+      return result;
     }
     if (method === "models.list") {
       return { models: catalog };
@@ -119,11 +129,17 @@ function createChatHeaderState(
     sessionKey: "main",
     connected: true,
     sessionsHideCron: true,
-    sessionsResult: createSessionsListResult({
-      model: currentModel,
-      modelProvider: currentModelProvider,
-      omitSessionFromList,
-    }),
+    sessionsResult: (() => {
+      const result = createSessionsListResult({
+        model: currentModel,
+        modelProvider: currentModelProvider,
+        omitSessionFromList,
+      });
+      if (result.sessions[0]) {
+        result.sessions[0].thinkingLevel = currentThinkingLevel ?? undefined;
+      }
+      return result;
+    })(),
     chatModelOverrides: {},
     chatModelCatalog: catalog,
     chatModelsLoading: false,
@@ -940,6 +956,72 @@ describe("chat view", () => {
     vi.unstubAllGlobals();
   });
 
+  it("shows the default thinking level in the chat header picker", async () => {
+    const { state } = createChatHeaderState({
+      model: "gpt-5",
+      modelProvider: "openai",
+    });
+    const container = document.createElement("div");
+    render(renderChatSessionSelect(state), container);
+
+    const thinkingSelect = container.querySelector<HTMLSelectElement>(
+      'select[data-chat-thinking-select="true"]',
+    );
+    expect(thinkingSelect).not.toBeNull();
+    expect(thinkingSelect?.value).toBe("");
+    expect(thinkingSelect?.options[0]?.textContent?.trim()).toBe("Default (off)");
+  });
+
+  it("patches the current session thinking level from the chat header picker", async () => {
+    const { state, request } = createChatHeaderState({
+      model: "gpt-5",
+      modelProvider: "openai",
+    });
+    const container = document.createElement("div");
+    render(renderChatSessionSelect(state), container);
+
+    const thinkingSelect = container.querySelector<HTMLSelectElement>(
+      'select[data-chat-thinking-select="true"]',
+    );
+    expect(thinkingSelect).not.toBeNull();
+
+    thinkingSelect!.value = "off";
+    thinkingSelect!.dispatchEvent(new Event("change", { bubbles: true }));
+    await flushTasks();
+
+    expect(request).toHaveBeenCalledWith("sessions.patch", {
+      key: "main",
+      thinkingLevel: "off",
+    });
+    expect(state.sessionsResult?.sessions[0]?.thinkingLevel).toBe("off");
+  });
+
+  it("clears the session thinking override back to the default thinking level", async () => {
+    const { state, request } = createChatHeaderState({
+      model: "gpt-5",
+      modelProvider: "openai",
+      thinkingLevel: "high",
+    });
+    const container = document.createElement("div");
+    render(renderChatSessionSelect(state), container);
+
+    const thinkingSelect = container.querySelector<HTMLSelectElement>(
+      'select[data-chat-thinking-select="true"]',
+    );
+    expect(thinkingSelect).not.toBeNull();
+    expect(thinkingSelect?.value).toBe("high");
+
+    thinkingSelect!.value = "";
+    thinkingSelect!.dispatchEvent(new Event("change", { bubbles: true }));
+    await flushTasks();
+
+    expect(request).toHaveBeenCalledWith("sessions.patch", {
+      key: "main",
+      thinkingLevel: null,
+    });
+    expect(state.sessionsResult?.sessions[0]?.thinkingLevel).toBeUndefined();
+  });
+
   it("reloads effective tools after a chat-header model switch for the active tools panel", async () => {
     vi.stubGlobal(
       "fetch",