diff --git a/packages/docs/content/models.en.md b/packages/docs/content/models.en.md
index 4fb5e61..f065c3c 100644
--- a/packages/docs/content/models.en.md
+++ b/packages/docs/content/models.en.md
@@ -77,7 +77,7 @@ Some models in the preset catalog: deepseek-v4-pro / deepseek-v4-flash, gemini-3
 
 ## Thinking levels
 
-Five levels: `none | low | medium | high | xhigh`, configured per Agent as `model.thinking_level` in `system_config.yaml`, default medium. The chat draft view offers a quick picker next to the model selector: a picked level is written back to the selected Agent's setting immediately (the switched-to level becomes that Agent's new default and applies from the next session; a running session keeps the level it was created with). See [Configuration](/configuration).
+Five levels: `none | low | medium | high | xhigh`, configured per Agent as `model.thinking_level` in `system_config.yaml`, default medium. The Web pickers offer `low` and above only (many models cannot disable thinking; `none` stays a valid stored value and still displays). The chat draft view offers a quick picker next to the model selector: a picked level is written back to the selected Agent's setting immediately (the switched-to level becomes that Agent's new default and applies from the next session; a running session keeps the level it was created with). See [Configuration](/configuration).
 
 ## Models decoupled from Agents
 
diff --git a/packages/docs/content/models.zh.md b/packages/docs/content/models.zh.md
index e296e56..c6578b6 100644
--- a/packages/docs/content/models.zh.md
+++ b/packages/docs/content/models.zh.md
@@ -77,7 +77,7 @@ api_key = "sk-..."
 
 ## 思考等级
 
-思考等级共五档：`none | low | medium | high | xhigh`，按 Agent 在 `system_config.yaml` 的 `model.thinking_level` 配置，默认 medium。对话草稿页在模型选择器旁提供快捷拾取器：选定档位立即写回所选 Agent 的该项配置（切换后的档位即成为该 Agent 的新默认，自下一个 Session 生效；进行中的 Session 沿用创建时的档位）。见 [配置参考](/configuration)。
+思考等级共五档：`none | low | medium | high | xhigh`，按 Agent 在 `system_config.yaml` 的 `model.thinking_level` 配置，默认 medium。Web 拾取器只提供 `low` 及以上档位（多数模型不支持关闭思考；`none` 仍是合法的已存值，能正常显示）。对话草稿页在模型选择器旁提供快捷拾取器：选定档位立即写回所选 Agent 的该项配置（切换后的档位即成为该 Agent 的新默认，自下一个 Session 生效；进行中的 Session 沿用创建时的档位）。见 [配置参考](/configuration)。
 
 ## 模型与 Agent 解耦
 
diff --git a/packages/web/e2e/draft.spec.mjs b/packages/web/e2e/draft.spec.mjs
index d127361..56b2fa7 100644
--- a/packages/web/e2e/draft.spec.mjs
+++ b/packages/web/e2e/draft.spec.mjs
@@ -87,14 +87,16 @@ test("draft: pick model/approval -> reload restores them -> send creates the ses
   await expect(page.getByRole("button", { name: "审批模式" })).toContainText("放行只读");
 
   // Conversation-time thinking level (backed by the Agent settings): the picker shows the
-  // seeded default (medium, short name 中); the menu carries a title bar and exactly the five
-  // short-name rows (no descriptions, no default row); picking 高 writes straight through to
-  // the Agent config, so the session created on send runs with it and it becomes the Agent's
-  // new default.
+  // seeded default (medium, short name 中); the menu carries a title bar and the short-name
+  // rows 低/中/高/极高 only — no descriptions, no default row, and no 无 (many models cannot
+  // disable thinking); picking 高 writes straight through to the Agent config, so the session
+  // created on send runs with it and it becomes the Agent's new default.
   const thinkingBtn = page.getByRole("button", { name: "思考等级" });
   await expect(thinkingBtn).toContainText("中");
   await thinkingBtn.click();
   await expect(page.getByText("思考等级", { exact: true })).toBeVisible(); // menu title bar
+  await expect(page.getByRole("button", { name: "低", exact: true })).toBeVisible();
+  await expect(page.getByRole("button", { name: "无", exact: true })).toHaveCount(0);
   await page.getByRole("button", { name: "高", exact: true }).click();
   await expect(thinkingBtn).toContainText("高");
   await expect
diff --git a/packages/web/src/features/agents/agent-settings-page.tsx b/packages/web/src/features/agents/agent-settings-page.tsx
index bb68477..1d0702e 100644
--- a/packages/web/src/features/agents/agent-settings-page.tsx
+++ b/packages/web/src/features/agents/agent-settings-page.tsx
@@ -31,6 +31,7 @@ import { Modal } from "../../components/ui/modal";
 import { Skeleton } from "../../components/ui/skeleton";
 import { VaultTab } from "./vault-tab";
 import { SchedulesTab } from "./schedules-tab";
+import { thinkingLevelOptionsFor } from "../chat/thinking-level";
 
 type TabKey = "overview" | "prompt" | "runtime" | "tools" | "vault" | "schedules";
 
@@ -500,7 +501,16 @@ function RuntimeTab({ data, onSave }: { data: AgentConfigResponse; onSave: SaveF
   };
 
   // S is reassigned on language switch (live binding), so read it during render rather than hoisting to a module-level constant.
-  const thinkingLevelOptions = withDefaultOption(S.agent.thinkingLevelOptions);
+  // "none" is no longer offered (many models cannot disable thinking) but stays a valid stored
+  // value: assembly lives in thinkingLevelOptionsFor, gated on the **persisted** config — a
+  // misclick onto another tier keeps the legacy row until the change is actually saved, so the
+  // stored value stays reachable (see thinking-level.ts).
+  const thinkingLevelOptions = thinkingLevelOptionsFor(
+    S.agent.thinkingLevelOptions,
+    S.agent.defaultValue,
+    S.agent.thinkingLevelNoneKept,
+    cfg.model?.thinkingLevel,
+  );
   const compactionModeOptions = withDefaultOption(S.agent.compactionModeOptions);
 
   return (
diff --git a/packages/web/src/features/chat/chat-input.tsx b/packages/web/src/features/chat/chat-input.tsx
index adb8ff6..6a4f0d4 100644
--- a/packages/web/src/features/chat/chat-input.tsx
+++ b/packages/web/src/features/chat/chat-input.tsx
@@ -64,7 +64,7 @@ import { ProviderLogo } from "../../components/ui/provider-logo";
 import { hasConfiguredKey, sameModelRef, visibleChatModels } from "../models/model-grouping";
 import { filterAgents, matchMention, splitLeadingMention } from "./agent-mentions";
 import { matchSlash, removeSlashToken } from "./slash-token";
-import { THINKING_LEVELS, thinkingLevelLabel } from "./thinking-level";
+import { SELECTABLE_THINKING_LEVELS, thinkingLevelLabel } from "./thinking-level";
 import {
   BOOK_ICON,
   buildSkillsMessage,
@@ -393,8 +393,10 @@ const SPARK_ICON = "M12 3l1.9 5.1L19 10l-5.1 1.9L12 17l-1.9-5.1L5 10l5.1-1.9L12
  * level straight through to the Agent settings — llmConfig is assembled once per session, so
  * the level applies to the session created on first send and becomes the Agent's new default
  * (switch-becomes-default). Per review: a title bar names the control, and the menu lists
- * exactly the five levels with short names only (no descriptions, no "default" row) — an
- * Agent without an explicit override shows an em dash until a level is picked.
+ * the selectable levels with short names only (no descriptions, no "default" row, and no
+ * "none" — many models cannot disable thinking); an Agent without an explicit override shows
+ * an em dash until a level is picked, and a stored legacy "none" still displays via the
+ * label table (just never offered).
  */
 function ThinkingLevelSelect({
   value,
@@ -449,7 +451,7 @@ function ThinkingLevelSelect({
       <div className="border-b border-gray-100 px-3 pb-1.5 pt-0.5 text-xs font-semibold text-gray-500 dark:border-gray-800 dark:text-gray-400">
         {S.chat.thinkingLevel}
       </div>
-      {THINKING_LEVELS.map((level) => (
+      {SELECTABLE_THINKING_LEVELS.map((level) => (
         <button
           key={level}
           type="button"
diff --git a/packages/web/src/features/chat/thinking-level.ts b/packages/web/src/features/chat/thinking-level.ts
index d421ffd..6d0ef4d 100644
--- a/packages/web/src/features/chat/thinking-level.ts
+++ b/packages/web/src/features/chat/thinking-level.ts
@@ -5,18 +5,29 @@
  * it shows the selected Agent's current level and writes a picked level straight through
  * to the Agent config, so the session created on first send — which reads systemConfig
  * fresh — runs with it, and it becomes the Agent's new default (switch-becomes-default).
- * Per review: the menu lists exactly the five levels with short names only (no
- * descriptions, no "default" row) under a title bar naming the control.
+ * Per review: the menu lists the levels with short names only (no descriptions, no
+ * "default" row) under a title bar naming the control — and it does **not** offer "none"
+ * (many models cannot disable thinking): "none" stays a valid stored/wire value, so a
+ * legacy config or session that carries it still displays via the label table below.
  */
 
-/** The five levels, in menu order (mirrors core's ThinkingLevelName). */
+/** All five stored/wire levels, for display lookup (mirrors core's ThinkingLevelName). */
 export const THINKING_LEVELS = ["none", "low", "medium", "high", "xhigh"] as const;
 
+/**
+ * The levels the picker offers, in menu order: "none" is deliberately excluded (many models
+ * don't support disabling thinking) — it can still be displayed (a stored legacy value) but
+ * never picked.
+ */
+export const SELECTABLE_THINKING_LEVELS = ["low", "medium", "high", "xhigh"] as const;
+
 /**
  * Short display label for a level from the localized name table (S.chat.thinkingLevelNames).
- * Returns null for anything outside the five levels — including "" (an Agent without an
- * explicit override) and session_meta's "default" — so callers can render a placeholder on
- * the trigger and hide the session read-only tag instead of showing a raw internal value.
+ * Covers all five stored levels including "none" (so a legacy value displays sanely instead
+ * of being rewritten or hidden). Returns null for anything else — including "" (an Agent
+ * without an explicit override) and session_meta's "default" — so callers can render a
+ * placeholder on the trigger and hide the session read-only tag instead of showing a raw
+ * internal value.
  */
 export function thinkingLevelLabel(
   names: Readonly<Record<string, string>>,
@@ -26,3 +37,46 @@ export function thinkingLevelLabel(
     ? (names[level] ?? level)
     : null;
 }
+
+/** One dropdown row of the agent-settings thinking-level menu (shape of OptionMenuChoice<string>). */
+export interface ThinkingLevelOptionRow {
+  value: string;
+  /** Compact text on the trigger button ("" renders the localized default tag). */
+  triggerLabel: string;
+  /** Panel row title. */
+  label: string;
+  /** Panel row description. */
+  description: string;
+}
+
+/**
+ * Assembles the agent-settings thinking-level dropdown rows from the dictionary's
+ * [value, description] pairs (which no longer include `none`). Backward compatibility:
+ * when the **persisted** config already stores `none` (a legacy value), a display-only
+ * row for it is appended — the trigger shows the real stored state instead of "—" and
+ * nothing is silently rewritten. Gating on the persisted value (not the local edit
+ * state) means a misclick onto another tier keeps the row until the change is actually
+ * saved, so the user can always click back to the value still stored on disk.
+ */
+export function thinkingLevelOptionsFor(
+  options: ReadonlyArray<readonly [string, string]>,
+  defaultTag: string,
+  noneKeptDescription: string,
+  storedLevel: string | undefined,
+): ThinkingLevelOptionRow[] {
+  const rows = options.map(([value, description]) => ({
+    value,
+    triggerLabel: value || defaultTag,
+    label: value || defaultTag,
+    description,
+  }));
+  if (storedLevel === "none") {
+    rows.push({
+      value: "none",
+      triggerLabel: "none",
+      label: "none",
+      description: noneKeptDescription,
+    });
+  }
+  return rows;
+}
diff --git a/packages/web/src/lib/strings-en.ts b/packages/web/src/lib/strings-en.ts
index e60acb4..858a8aa 100644
--- a/packages/web/src/lib/strings-en.ts
+++ b/packages/web/src/lib/strings-en.ts
@@ -197,7 +197,6 @@ export const en: Strings = {
     thinkingLevel: "model.thinking_level",
     thinkingLevelOptions: [
       ["", "Send no override — keep whatever is currently configured."],
-      ["none", "Disables extended reasoning; the fastest responses."],
       ["low", "Enables a lower tier of extended reasoning."],
       [
         "medium",
@@ -209,6 +208,8 @@ export const en: Strings = {
         "Enables the highest tier of extended reasoning; identical to high on some models.",
       ],
     ] as ReadonlyArray<readonly [string, string]>,
+    thinkingLevelNoneKept:
+      "Stored legacy tier: new selections no longer offer the off tier (many models cannot disable thinking).",
     timeoutMs: "model.timeoutMs",
     timeoutMsHint: "Per-request timeout, ms",
     compaction: "Context compaction",
diff --git a/packages/web/src/lib/strings.ts b/packages/web/src/lib/strings.ts
index 2bbf191..4f2b18c 100644
--- a/packages/web/src/lib/strings.ts
+++ b/packages/web/src/lib/strings.ts
@@ -188,14 +188,16 @@ export const zh = {
     maxTurns: "max_turns（单 Task 最大轮次，-1 不限制）",
     maxTokens: "model.max_tokens",
     thinkingLevel: "model.thinking_level",
+    /** Selectable tiers exclude `none` (many models cannot disable thinking); a stored `none` still displays — see `thinkingLevelNoneKept`. */
     thinkingLevelOptions: [
       ["", "不提交覆盖值，沿用当前生效的配置。"],
-      ["none", "关闭扩展推理，响应最快。"],
       ["low", "开启较低强度的扩展推理。"],
       ["medium", "开启中等强度的扩展推理（新建 Agent 的缺省档位）。"],
       ["high", "开启较高强度的扩展推理，响应更慢。"],
       ["xhigh", "开启最高强度的扩展推理，部分模型上效果与 high 相同。"],
     ] as ReadonlyArray<readonly [string, string]>,
+    /** Row description shown only while the stored config is `none`: displayed as-is, never rewritten, and no longer offered as a choice. */
+    thinkingLevelNoneKept: "已存的历史档位：新选择不再提供关闭档（多数模型不支持关闭思考）。",
     timeoutMs: "model.timeoutMs",
     timeoutMsHint: "单次 Request 超时，毫秒",
     compaction: "上下文压缩（compaction）",
@@ -463,7 +465,7 @@ export const zh = {
     chooseAgent: "选择 Agent",
     chooseModel: "选择模型",
     thinkingLevel: "思考等级",
-    /** 会话前拾取器的档位短名（评审要求：只写短名、不带说明、无“缺省”项）。 */
+    /** Short tier names for the pre-conversation picker (per review: short names only, no descriptions, no "default" row). `none` exists purely to display a stored legacy value — it is never offered as a choice (many models cannot disable thinking). */
     thinkingLevelNames: {
       none: "无",
       low: "低",
diff --git a/packages/web/test/thinking-level.test.ts b/packages/web/test/thinking-level.test.ts
index fdce904..52a105c 100644
--- a/packages/web/test/thinking-level.test.ts
+++ b/packages/web/test/thinking-level.test.ts
@@ -1,10 +1,16 @@
 /**
- * thinking-level.ts unit tests: the conversation-time picker's short-name lookup — the five
- * levels map to their localized names, while "" (no override yet) and session_meta's
- * "default" resolve to null (trigger shows a placeholder; the session tag hides).
+ * thinking-level.ts unit tests: the conversation-time picker's short-name lookup and the
+ * selectable list — the picker offers only low/medium/high/xhigh (many models cannot disable
+ * thinking), while "none" stays a displayable stored value; "" (no override yet) and
+ * session_meta's "default" resolve to null (trigger shows a placeholder; the session tag hides).
  */
 import { describe, expect, it } from "vitest";
-import { THINKING_LEVELS, thinkingLevelLabel } from "../src/features/chat/thinking-level";
+import {
+  SELECTABLE_THINKING_LEVELS,
+  THINKING_LEVELS,
+  thinkingLevelLabel,
+  thinkingLevelOptionsFor,
+} from "../src/features/chat/thinking-level";
 
 /** Mirrors the shape of S.chat.thinkingLevelNames. */
 const NAMES: Readonly<Record<string, string>> = {
@@ -15,8 +21,13 @@ const NAMES: Readonly<Record<string, string>> = {
   xhigh: "Extreme High",
 };
 
-describe("thinkingLevelLabel", () => {
-  it("maps each of the five levels to its localized short name (menu order preserved)", () => {
+describe("thinking level lists", () => {
+  it("offers only low/medium/high/xhigh — no 'none' (many models cannot disable thinking)", () => {
+    expect(SELECTABLE_THINKING_LEVELS).toEqual(["low", "medium", "high", "xhigh"]);
+    expect(SELECTABLE_THINKING_LEVELS).not.toContain("none");
+  });
+
+  it("keeps all five stored levels displayable (a legacy 'none' is shown, never offered)", () => {
     expect(THINKING_LEVELS).toEqual(["none", "low", "medium", "high", "xhigh"]);
     expect(THINKING_LEVELS.map((l) => thinkingLevelLabel(NAMES, l))).toEqual([
       "None",
@@ -26,7 +37,9 @@ describe("thinkingLevelLabel", () => {
       "Extreme High",
     ]);
   });
+});
 
+describe("thinkingLevelLabel", () => {
   it("returns null for non-levels: '' (no override yet), session_meta's 'default', unknown, null", () => {
     expect(thinkingLevelLabel(NAMES, "")).toBeNull();
     expect(thinkingLevelLabel(NAMES, "default")).toBeNull();
@@ -39,3 +52,34 @@ describe("thinkingLevelLabel", () => {
     expect(thinkingLevelLabel({}, "medium")).toBe("medium");
   });
 });
+
+describe("thinkingLevelOptionsFor (agent-settings dropdown assembly)", () => {
+  /** Mirrors the shape of S.agent.thinkingLevelOptions after the none row's removal. */
+  const OPTIONS: ReadonlyArray<readonly [string, string]> = [
+    ["", "Send no override."],
+    ["low", "Low tier."],
+    ["medium", "Medium tier."],
+    ["high", "High tier."],
+    ["xhigh", "Extra-high tier."],
+  ];
+
+  it("maps the dictionary in order; the '' row renders the default tag; no none row normally", () => {
+    for (const stored of [undefined, "", "medium", "xhigh"]) {
+      const rows = thinkingLevelOptionsFor(OPTIONS, "(default)", "legacy none", stored);
+      expect(rows.map((r) => r.value)).toEqual(["", "low", "medium", "high", "xhigh"]);
+      expect(rows[0]).toMatchObject({ triggerLabel: "(default)", label: "(default)" });
+      expect(rows.some((r) => r.value === "none")).toBe(false);
+    }
+  });
+
+  it("appends a display-only none row when the persisted config stores none (backward compat)", () => {
+    const rows = thinkingLevelOptionsFor(OPTIONS, "(default)", "legacy none", "none");
+    expect(rows.map((r) => r.value)).toEqual(["", "low", "medium", "high", "xhigh", "none"]);
+    expect(rows.at(-1)).toEqual({
+      value: "none",
+      triggerLabel: "none",
+      label: "none",
+      description: "legacy none",
+    });
+  });
+});