diff --git a/packages/kilo-i18n/src/ar.ts b/packages/kilo-i18n/src/ar.ts
index 4a8cd1c79ff..87a99ef423b 100644
--- a/packages/kilo-i18n/src/ar.ts
+++ b/packages/kilo-i18n/src/ar.ts
@@ -11,4 +11,7 @@ export const dict = {
   // Provider dialog translations
   "dialog.provider.group.recommended": "موصى به",
   "dialog.provider.kilo.note": "الوصول إلى أكثر من 500 نموذج ذكاء اصطناعي",
+
+  // Reasoning block label
+  "ui.reasoning.label": "الاستدلال",
 }
diff --git a/packages/kilo-i18n/src/br.ts b/packages/kilo-i18n/src/br.ts
index 4734a98d0f4..fe1c553ba2c 100644
--- a/packages/kilo-i18n/src/br.ts
+++ b/packages/kilo-i18n/src/br.ts
@@ -11,4 +11,7 @@ export const dict = {
   // Provider dialog translations
   "dialog.provider.group.recommended": "Recomendados",
   "dialog.provider.kilo.note": "Acesso a mais de 500 modelos de IA",
+
+  // Reasoning block label
+  "ui.reasoning.label": "Raciocínio",
 }
diff --git a/packages/kilo-i18n/src/bs.ts b/packages/kilo-i18n/src/bs.ts
index 28025010251..96dd911fd11 100644
--- a/packages/kilo-i18n/src/bs.ts
+++ b/packages/kilo-i18n/src/bs.ts
@@ -16,4 +16,7 @@ export const dict = {
   "desktop.menu.reloadWebview": "Ponovno učitavanje webview-a",
   "desktop.updater.installFailed.message": "Neuspjelo instaliranje ažuriranja",
   "desktop.cli.installed.message": "CLI je instaliran u {{path}}\n\nRestartuj terminal da bi koristio komandu 'kilo'.",
+
+  // Reasoning block label
+  "ui.reasoning.label": "Rezonovanje",
 }
diff --git a/packages/kilo-i18n/src/da.ts b/packages/kilo-i18n/src/da.ts
index 16f0c8f6828..e07c99b0268 100644
--- a/packages/kilo-i18n/src/da.ts
+++ b/packages/kilo-i18n/src/da.ts
@@ -11,4 +11,7 @@ export const dict = {
   // Provider dialog translations
   "dialog.provider.group.recommended": "Anbefalede",
   "dialog.provider.kilo.note": "Adgang til 500+ AI-modeller",
+
+  // Reasoning block label
+  "ui.reasoning.label": "Ræsonnement",
 }
diff --git a/packages/kilo-i18n/src/de.ts b/packages/kilo-i18n/src/de.ts
index b39b7eb4776..40478b3c35a 100644
--- a/packages/kilo-i18n/src/de.ts
+++ b/packages/kilo-i18n/src/de.ts
@@ -11,4 +11,7 @@ export const dict = {
   // Provider dialog translations
   "dialog.provider.group.recommended": "Empfohlen",
   "dialog.provider.kilo.note": "Zugriff auf 500+ KI-Modelle",
+
+  // Reasoning block label
+  "ui.reasoning.label": "Denken",
 }
diff --git a/packages/kilo-i18n/src/en.ts b/packages/kilo-i18n/src/en.ts
index 070c3d41cea..4c03f296e18 100644
--- a/packages/kilo-i18n/src/en.ts
+++ b/packages/kilo-i18n/src/en.ts
@@ -14,6 +14,9 @@ export const dict = {
   "dialog.provider.group.recommended": "Recommended",
   "dialog.provider.kilo.note": "Access 500+ AI models",
 
+  // Reasoning block label
+  "ui.reasoning.label": "Reasoning",
+
   // Add any upstream overrides below this line
   // Example: "some.upstream.key": "Kilo-specific override value",
 }
diff --git a/packages/kilo-i18n/src/es.ts b/packages/kilo-i18n/src/es.ts
index 25c5dba9f36..b8bd8c27f75 100644
--- a/packages/kilo-i18n/src/es.ts
+++ b/packages/kilo-i18n/src/es.ts
@@ -11,4 +11,7 @@ export const dict = {
   // Provider dialog translations
   "dialog.provider.group.recommended": "Recomendados",
   "dialog.provider.kilo.note": "Acceso a más de 500 modelos de IA",
+
+  // Reasoning block label
+  "ui.reasoning.label": "Razonamiento",
 }
diff --git a/packages/kilo-i18n/src/fr.ts b/packages/kilo-i18n/src/fr.ts
index d593e4a2be3..70797589a53 100644
--- a/packages/kilo-i18n/src/fr.ts
+++ b/packages/kilo-i18n/src/fr.ts
@@ -11,4 +11,7 @@ export const dict = {
   // Provider dialog translations
   "dialog.provider.group.recommended": "Recommandés",
   "dialog.provider.kilo.note": "Accès à plus de 500 modèles d'IA",
+
+  // Reasoning block label
+  "ui.reasoning.label": "Raisonnement",
 }
diff --git a/packages/kilo-i18n/src/ja.ts b/packages/kilo-i18n/src/ja.ts
index 08eda7545aa..cbb255ee25e 100644
--- a/packages/kilo-i18n/src/ja.ts
+++ b/packages/kilo-i18n/src/ja.ts
@@ -10,4 +10,7 @@ export const dict = {
   // Provider dialog translations
   "dialog.provider.group.recommended": "おすすめ",
   "dialog.provider.kilo.note": "500以上のAIモデルにアクセス",
+
+  // Reasoning block label
+  "ui.reasoning.label": "推論",
 }
diff --git a/packages/kilo-i18n/src/ko.ts b/packages/kilo-i18n/src/ko.ts
index cbbd28aa1f3..5aba34cea40 100644
--- a/packages/kilo-i18n/src/ko.ts
+++ b/packages/kilo-i18n/src/ko.ts
@@ -10,4 +10,7 @@ export const dict = {
   // Provider dialog translations
   "dialog.provider.group.recommended": "추천",
   "dialog.provider.kilo.note": "500개 이상의 AI 모델 이용 가능",
+
+  // Reasoning block label
+  "ui.reasoning.label": "추론",
 }
diff --git a/packages/kilo-i18n/src/no.ts b/packages/kilo-i18n/src/no.ts
index bd17fff9b59..0c141192528 100644
--- a/packages/kilo-i18n/src/no.ts
+++ b/packages/kilo-i18n/src/no.ts
@@ -11,4 +11,7 @@ export const dict = {
   // Provider dialog translations
   "dialog.provider.group.recommended": "Anbefalt",
   "dialog.provider.kilo.note": "Tilgang til 500+ AI-modeller",
+
+  // Reasoning block label
+  "ui.reasoning.label": "Resonnement",
 }
diff --git a/packages/kilo-i18n/src/pl.ts b/packages/kilo-i18n/src/pl.ts
index 63aea01e6e3..363e04aa235 100644
--- a/packages/kilo-i18n/src/pl.ts
+++ b/packages/kilo-i18n/src/pl.ts
@@ -11,4 +11,7 @@ export const dict = {
   // Provider dialog translations
   "dialog.provider.group.recommended": "Polecane",
   "dialog.provider.kilo.note": "Dostęp do ponad 500 modeli AI",
+
+  // Reasoning block label
+  "ui.reasoning.label": "Rozumowanie",
 }
diff --git a/packages/kilo-i18n/src/ru.ts b/packages/kilo-i18n/src/ru.ts
index 7a0276ad710..0509880741b 100644
--- a/packages/kilo-i18n/src/ru.ts
+++ b/packages/kilo-i18n/src/ru.ts
@@ -11,4 +11,7 @@ export const dict = {
   // Provider dialog translations
   "dialog.provider.group.recommended": "Рекомендуемые",
   "dialog.provider.kilo.note": "Доступ к 500+ моделям ИИ",
+
+  // Reasoning block label
+  "ui.reasoning.label": "Рассуждение",
 }
diff --git a/packages/kilo-i18n/src/th.ts b/packages/kilo-i18n/src/th.ts
index d6f88c10b10..688f92fe4b6 100644
--- a/packages/kilo-i18n/src/th.ts
+++ b/packages/kilo-i18n/src/th.ts
@@ -11,4 +11,7 @@ export const dict = {
   // Provider dialog translations
   "dialog.provider.group.recommended": "แนะนำ",
   "dialog.provider.kilo.note": "เข้าถึงโมเดล AI มากกว่า 500 รายการ",
+
+  // Reasoning block label
+  "ui.reasoning.label": "การให้เหตุผล",
 }
diff --git a/packages/kilo-i18n/src/zh.ts b/packages/kilo-i18n/src/zh.ts
index 93d0f4f6c0d..a864cdbcd48 100644
--- a/packages/kilo-i18n/src/zh.ts
+++ b/packages/kilo-i18n/src/zh.ts
@@ -9,4 +9,7 @@ export const dict = {
   // Provider dialog translations
   "dialog.provider.group.recommended": "推荐",
   "dialog.provider.kilo.note": "访问 500+ AI 模型",
+
+  // Reasoning block label
+  "ui.reasoning.label": "推理",
 }
diff --git a/packages/kilo-i18n/src/zht.ts b/packages/kilo-i18n/src/zht.ts
index a5b9a019f62..f8ea5697a64 100644
--- a/packages/kilo-i18n/src/zht.ts
+++ b/packages/kilo-i18n/src/zht.ts
@@ -9,4 +9,7 @@ export const dict = {
   // Provider dialog translations
   "dialog.provider.group.recommended": "推薦",
   "dialog.provider.kilo.note": "存取 500+ AI 模型",
+
+  // Reasoning block label
+  "ui.reasoning.label": "推理",
 }
diff --git a/packages/kilo-ui/src/components/message-part.css b/packages/kilo-ui/src/components/message-part.css
index 063a52330f8..f7b84895501 100644
--- a/packages/kilo-ui/src/components/message-part.css
+++ b/packages/kilo-ui/src/components/message-part.css
@@ -117,3 +117,64 @@ html[data-theme="kilo-vscode"] [data-component="bash-output"] {
 [data-component="question-answers"] {
   padding: 8px;
 }
+
+/* Reasoning block: visually distinct from normal agent output */
+[data-component="reasoning-part"] {
+  width: 100%;
+  border-left: 2px solid var(--border-weak-base);
+  border-radius: var(--radius-sm);
+  overflow: hidden;
+
+  [data-component="collapsible"].tool-collapsible {
+    gap: 0;
+  }
+
+  [data-slot="collapsible-trigger"] {
+    height: 28px;
+    padding: 0 8px;
+    gap: 6px;
+    background: var(--surface-inset-base);
+    border-radius: 0;
+    cursor: pointer;
+  }
+
+  [data-slot="reasoning-header"] {
+    display: flex;
+    flex: 1 1 auto;
+    align-items: center;
+    gap: 6px;
+    color: var(--text-weaker);
+    font-size: var(--font-size-small);
+    font-weight: var(--font-weight-medium);
+    min-width: 0;
+
+    [data-component="icon"] {
+      flex-shrink: 0;
+      color: var(--icon-weak-base);
+    }
+  }
+
+  [data-slot="reasoning-label"] {
+    overflow: hidden;
+    text-overflow: ellipsis;
+    white-space: nowrap;
+  }
+
+  [data-slot="reasoning-content"] {
+    padding: 8px 10px;
+    background: var(--surface-inset-base);
+
+    [data-component="markdown"] {
+      margin-top: 0;
+      font-style: italic;
+      font-size: var(--font-size-small);
+      color: var(--text-weak);
+      opacity: 0.9;
+
+      strong,
+      b {
+        color: var(--text-weak);
+      }
+    }
+  }
+}
diff --git a/packages/kilo-ui/src/components/message-part.tsx b/packages/kilo-ui/src/components/message-part.tsx
index 5b83670bb08..157e015f9e8 100644
--- a/packages/kilo-ui/src/components/message-part.tsx
+++ b/packages/kilo-ui/src/components/message-part.tsx
@@ -1 +1,41 @@
 export * from "@opencode-ai/ui/message-part"
+
+import { Show, createSignal } from "solid-js"
+import { PART_MAPPING } from "@opencode-ai/ui/message-part"
+import { Collapsible } from "@opencode-ai/ui/collapsible"
+import { Icon } from "@opencode-ai/ui/icon"
+import { Markdown } from "@opencode-ai/ui/markdown"
+import { useI18n } from "@opencode-ai/ui/context/i18n"
+import type { ReasoningPart } from "@kilocode/sdk/v2"
+import type { MessagePartProps } from "@opencode-ai/ui/message-part"
+
+// Override: collapsible reasoning block with brain icon + label
+// Replaces the upstream flat markdown render with a clearly distinguished, collapsed-by-default block
+PART_MAPPING["reasoning"] = function ReasoningPartDisplay(props: MessagePartProps) {
+  const part = props.part as unknown as ReasoningPart
+  const i18n = useI18n()
+  const [open, setOpen] = createSignal(false)
+  // Filter out redacted reasoning chunks from OpenRouter (encrypted reasoning data appears as [REDACTED])
+  const text = () => (part.text ?? "").replace("[REDACTED]", "").trim()
+
+  return (
+    <Show when={text()}>
+      <div data-component="reasoning-part">
+        <Collapsible open={open()} onOpenChange={setOpen}>
+          <Collapsible.Trigger>
+            <div data-slot="reasoning-header">
+              <Icon name="brain" size="small" />
+              <span data-slot="reasoning-label">{i18n.t("ui.reasoning.label" as never)}</span>
+            </div>
+            <Collapsible.Arrow />
+          </Collapsible.Trigger>
+          <Collapsible.Content>
+            <div data-slot="reasoning-content">
+              <Markdown text={text()} cacheKey={part.id} />
+            </div>
+          </Collapsible.Content>
+        </Collapsible>
+      </div>
+    </Show>
+  )
+}
diff --git a/packages/kilo-ui/src/stories/message-part.stories.tsx b/packages/kilo-ui/src/stories/message-part.stories.tsx
index 812c562bc0f..d2b546c3b59 100644
--- a/packages/kilo-ui/src/stories/message-part.stories.tsx
+++ b/packages/kilo-ui/src/stories/message-part.stories.tsx
@@ -1,6 +1,8 @@
 /** @jsxImportSource solid-js */
 import type { Meta, StoryObj } from "storybook-solidjs-vite"
 import { Message, AssistantMessageDisplay, UserMessageDisplay } from "@opencode-ai/ui/message-part"
+// Side-effect import: registers kilo-ui's PART_MAPPING override for reasoning blocks
+import "../components/message-part"
 import { DataProvider } from "@opencode-ai/ui/context/data"
 import { DiffComponentProvider } from "@opencode-ai/ui/context/diff"
 import { CodeComponentProvider } from "@opencode-ai/ui/context/code"
@@ -8,7 +10,7 @@ import { DialogProvider } from "@opencode-ai/ui/context/dialog"
 import { MarkedProvider } from "@opencode-ai/ui/context/marked"
 import { Diff } from "@opencode-ai/ui/diff"
 import { Code } from "@opencode-ai/ui/code"
-import type { UserMessage, AssistantMessage, TextPart, ToolPart } from "@kilocode/sdk/v2"
+import type { UserMessage, AssistantMessage, TextPart, ToolPart, ReasoningPart } from "@kilocode/sdk/v2"
 
 const SESSION_ID = "session-story-001"
 const USER_MSG_ID = "user-msg-001"
@@ -104,6 +106,15 @@ const errorToolPart: ToolPart = {
   },
 }
 
+const reasoningPart: ReasoningPart = {
+  id: "part-reasoning-001",
+  sessionID: SESSION_ID,
+  messageID: ASST_MSG_ID,
+  type: "reasoning",
+  text: "Let me think about this carefully. The user wants code improvements.\n\n1. First, I should check for error boundaries — they prevent cascading failures\n2. The dependencies could be updated to newer minor versions\n3. Unit tests would improve confidence in refactoring later\n\nI'll structure my response to address each point clearly.",
+  time: { start: now - 9000, end: now - 8500 },
+}
+
 const mockData = {
   session: [],
   session_status: {},
@@ -186,6 +197,33 @@ export const FullConversationTurn: Story = {
   ),
 }
 
+export const WithReasoningCollapsed: Story = {
+  name: "WithReasoning (collapsed)",
+  render: () => (
+    <AllProviders>
+      <AssistantMessageDisplay message={mockAssistantMessage} parts={[reasoningPart, textPart]} />
+    </AllProviders>
+  ),
+}
+
+export const WithReasoningExpanded: Story = {
+  name: "WithReasoning (expanded)",
+  render: () => {
+    // Use a wrapper to render with the collapsible open by default
+    const expandedReasoningPart = { ...reasoningPart, id: "part-reasoning-expanded" }
+    return (
+      <AllProviders>
+        <AssistantMessageDisplay message={mockAssistantMessage} parts={[expandedReasoningPart, textPart]} />
+      </AllProviders>
+    )
+  },
+  play: async ({ canvasElement }: { canvasElement: HTMLElement }) => {
+    // Click the collapsible trigger to expand it
+    const trigger = canvasElement.querySelector("[data-slot='reasoning-header']")?.closest("button")
+    if (trigger) trigger.click()
+  },
+}
+
 export const MessageSwitch: Story = {
   render: () => (
     <AllProviders>
diff --git a/packages/kilo-ui/tests/visual-regression.spec.ts-snapshots/components-messagepart/with-reasoning-collapsed-chromium-linux.png b/packages/kilo-ui/tests/visual-regression.spec.ts-snapshots/components-messagepart/with-reasoning-collapsed-chromium-linux.png
new file mode 100644
index 00000000000..fdf49245b20
--- /dev/null
+++ b/packages/kilo-ui/tests/visual-regression.spec.ts-snapshots/components-messagepart/with-reasoning-collapsed-chromium-linux.png
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:cf93ca79d15deab7dc52473f68305b521c62d10e968a9258e09609ad9c04fde6
+size 15837
diff --git a/packages/kilo-ui/tests/visual-regression.spec.ts-snapshots/components-messagepart/with-reasoning-expanded-chromium-linux.png b/packages/kilo-ui/tests/visual-regression.spec.ts-snapshots/components-messagepart/with-reasoning-expanded-chromium-linux.png
new file mode 100644
index 00000000000..3da58463454
--- /dev/null
+++ b/packages/kilo-ui/tests/visual-regression.spec.ts-snapshots/components-messagepart/with-reasoning-expanded-chromium-linux.png
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:14bf991adcbc6fcbf53f4cff2275dcec255943b5545c624231aeb73529ca2d6e
+size 32478