diff --git a/.changeset/custom-output-styles.md b/.changeset/custom-output-styles.md
new file mode 100644
index 000000000..59b1343d2
--- /dev/null
+++ b/.changeset/custom-output-styles.md
@@ -0,0 +1,6 @@
+---
+"@moonshot-ai/kimi-code-sdk": minor
+"@moonshot-ai/kimi-code": minor
+---
+
+Add custom output styles. Markdown style files — built-in `concise` and `explanatory`, plus your own under `<project>/.kimi-code/output-styles/` and `~/.kimi-code/output-styles/` — are injected additively into the system prompt to shape the assistant's tone, format, and verbosity. Select one with the `output_style` config key (precedence: project > user > built-in).
diff --git a/docs/.vitepress/config.ts b/docs/.vitepress/config.ts
index f35266ad5..ae93a0fde 100644
--- a/docs/.vitepress/config.ts
+++ b/docs/.vitepress/config.ts
@@ -69,6 +69,7 @@ const config = withMermaid(defineConfig({
                 { text: 'Agent 与子 Agent', link: '/zh/customization/agents' },
                 { text: 'Hooks', link: '/zh/customization/hooks' },
                 { text: '自定义主题', link: '/zh/customization/themes' },
+                { text: '输出风格', link: '/zh/customization/output-styles' },
               ],
             },
           ],
@@ -146,6 +147,7 @@ const config = withMermaid(defineConfig({
                 { text: 'Agents and Subagents', link: '/en/customization/agents' },
                 { text: 'Hooks', link: '/en/customization/hooks' },
                 { text: 'Custom Themes', link: '/en/customization/themes' },
+                { text: 'Output Styles', link: '/en/customization/output-styles' },
               ],
             },
           ],
diff --git a/docs/en/customization/output-styles.md b/docs/en/customization/output-styles.md
new file mode 100644
index 000000000..451b7f392
--- /dev/null
+++ b/docs/en/customization/output-styles.md
@@ -0,0 +1,63 @@
+# Custom Output Styles
+
+An output style is a set of instructions injected into Kimi Code's system prompt to shape **how** the assistant responds — its tone, format, and verbosity. Styles are **additive**: they layer on top of Kimi Code's default behavior and never override correctness, safety, or what a task actually requires. Two styles are built in (`concise` and `explanatory`), and you can add your own as Markdown files.
+
+## Built-in styles
+
+| Name | What it does |
+| --- | --- |
+| `concise` | Terse, minimal-prose responses focused on the result — skips preamble, restating the question, and summaries unless asked. |
+| `explanatory` | Explains the reasoning behind notable decisions and trade-offs, teaching as it works. |
+
+Built-in styles always exist. A style file you create with the same name overrides the built-in one.
+
+## Create a style
+
+Add a `.md` file to an output-styles directory:
+
+- **Project scope** — `<git-root>/.kimi-code/output-styles/`, where `<git-root>` is the nearest ancestor of the working directory that contains a `.git` directory (or the working directory itself when there is no git repository). Style files in other subdirectories are not scanned.
+- **User scope** — `~/.kimi-code/output-styles/`, or `$KIMI_CODE_HOME/output-styles/` when the `KIMI_CODE_HOME` environment variable is set
+
+Style files are read from the local filesystem, so when you run Kimi Code against a remote host (for example over SSH), keep your style files on the local machine.
+
+Create the directory if it does not exist. The **filename is the style name** when no `name` is set in the frontmatter: `socratic.md` becomes the style `socratic`.
+
+A style file is optional YAML frontmatter followed by the instruction body:
+
+```md
+---
+name: socratic
+description: Answers with guiding questions instead of handing over solutions.
+---
+Guide the user toward the answer with focused questions rather than handing over
+the full solution immediately. Once they are close, confirm and fill in the
+remaining details. Keep each reply short.
+```
+
+Fields:
+
+- `name` (optional): the style identifier. Falls back to the filename without `.md`.
+- `description` (optional): a human-readable summary. Falls back to the first non-empty line of the body.
+- **body** (required): the instructions injected into the system prompt. A file with an empty body is skipped.
+
+## Precedence
+
+When more than one scope defines a style with the same name, the more specific scope wins: **project overrides user overrides built-in**.
+
+## Select a style
+
+Set `output_style` to the style name in `config.toml`:
+
+```toml
+# ~/.kimi-code/config.toml
+output_style = "concise"
+```
+
+`output_style` is applied when an agent's system prompt is built. A **new session's** main agent uses the current value, and subagents pick it up on every spawn. An already-running session keeps its main agent's system prompt, so `/reload` and resume do **not** change the main agent's style — start a new session to apply a change. Leave `output_style` unset for the default behavior.
+
+## What happens on errors
+
+Output styles are designed never to block startup:
+
+- **An invalid or empty style file** (malformed YAML frontmatter, empty body): that file is skipped; the other styles still load.
+- **`output_style` names a style that does not exist**: no style is injected, and Kimi Code runs with its default behavior.
diff --git a/docs/zh/customization/output-styles.md b/docs/zh/customization/output-styles.md
new file mode 100644
index 000000000..4691ff488
--- /dev/null
+++ b/docs/zh/customization/output-styles.md
@@ -0,0 +1,62 @@
+# 自定义输出风格
+
+输出风格（output style）是一段注入到 Kimi Code 系统提示中的指令，用来塑造助手**如何**回应——它的语气、格式和详略程度。风格是**叠加式**的：它们叠加在 Kimi Code 的默认行为之上，绝不会覆盖正确性、安全性，或任务本身真正的要求。内置了两种风格（`concise` 和 `explanatory`），你也可以用 Markdown 文件添加自己的风格。
+
+## 内置风格
+
+| 名称 | 作用 |
+| --- | --- |
+| `concise` | 简短、少废话、聚焦结果的回应——除非被要求，否则省略开场白、复述问题和总结。 |
+| `explanatory` | 解释关键决策与取舍背后的理由，一边做一边讲解。 |
+
+内置风格始终存在。你创建的同名风格文件会覆盖内置的那一个。
+
+## 创建一个风格
+
+在某个 output-styles 目录下新建一个 `.md` 文件：
+
+- **项目作用域** —— `<git-根>/.kimi-code/output-styles/`，其中 `<git-根>` 是工作目录向上最近的、包含 `.git` 的祖先目录（若不在 git 仓库中，则为工作目录本身）。其他子目录中的风格文件不会被扫描。
+- **用户作用域** —— `~/.kimi-code/output-styles/`，或在设置了 `KIMI_CODE_HOME` 环境变量时为 `$KIMI_CODE_HOME/output-styles/`
+
+风格文件从本地文件系统读取；当你通过 SSH 等方式连接远程主机运行 Kimi Code 时，请把风格文件放在本地机器上。
+
+目录不存在就自己建一个。当 frontmatter 中没有写 `name` 时，**文件名就是风格名**：`socratic.md` 会成为风格 `socratic`。
+
+一个风格文件由可选的 YAML frontmatter 加上指令正文组成：
+
+```md
+---
+name: socratic
+description: 用引导式提问代替直接给出答案。
+---
+用有针对性的问题引导用户逼近答案，而不是一上来就把完整方案给出去。
+当用户接近答案时，确认并补全剩余细节。每次回复都尽量简短。
+```
+
+字段：
+
+- `name`（可选）：风格标识。缺省时回退为去掉 `.md` 的文件名。
+- `description`（可选）：便于阅读的简介。缺省时回退为正文的第一行非空内容。
+- **正文**（必填）：注入到系统提示中的指令。正文为空的文件会被跳过。
+
+## 优先级
+
+当多个作用域定义了同名风格时，更具体的作用域胜出：**项目覆盖用户，用户覆盖内置**。
+
+## 选择一个风格
+
+在 `config.toml` 中把 `output_style` 设为风格名：
+
+```toml
+# ~/.kimi-code/config.toml
+output_style = "concise"
+```
+
+`output_style` 在构建 Agent 的系统提示时生效。**新会话**的主 Agent 使用当前值，子 Agent 则在每次生成时读取当前值。已在运行的会话会保留其主 Agent 的系统提示，因此 `/reload` 和恢复（resume）**不会**改变主 Agent 的风格——要应用更改请开启新会话。不设置 `output_style` 即为默认行为。
+
+## 出错时会发生什么
+
+输出风格的设计目标是绝不阻塞启动：
+
+- **无效或空的风格文件**（frontmatter 格式错误、正文为空）：该文件会被跳过；其余风格照常加载。
+- **`output_style` 指向一个不存在的风格**：不会注入任何风格，Kimi Code 以默认行为运行。
diff --git a/packages/agent-core/src/agent/index.ts b/packages/agent-core/src/agent/index.ts
index ea1cd806f..9a3a361de 100644
--- a/packages/agent-core/src/agent/index.ts
+++ b/packages/agent-core/src/agent/index.ts
@@ -238,6 +238,7 @@ export class Agent {
       skills: this.skills?.registry,
       cwdListing: context?.cwdListing,
       agentsMd: context?.agentsMd,
+      outputStyleBody: context?.outputStyleBody,
     });
     this.config.update({ profileName: profile.name, systemPrompt });
     this.tools.setActiveTools(profile.tools);
diff --git a/packages/agent-core/src/config/schema.ts b/packages/agent-core/src/config/schema.ts
index 9b3d11cf0..1c49d0a66 100644
--- a/packages/agent-core/src/config/schema.ts
+++ b/packages/agent-core/src/config/schema.ts
@@ -216,6 +216,7 @@ export const KimiConfigSchema = z.object({
   services: ServicesConfigSchema.optional(),
   mergeAllAvailableSkills: z.boolean().optional(),
   extraSkillDirs: z.array(z.string()).optional(),
+  outputStyle: z.string().optional(),
   loopControl: LoopControlSchema.optional(),
   background: BackgroundConfigSchema.optional(),
   experimental: ExperimentalConfigSchema.optional(),
@@ -255,6 +256,7 @@ export const KimiConfigPatchSchema = z
     services: ServicesConfigPatchSchema.optional(),
     mergeAllAvailableSkills: z.boolean().optional(),
     extraSkillDirs: z.array(z.string()).optional(),
+    outputStyle: z.string().optional(),
     loopControl: LoopControlPatchSchema.optional(),
     background: BackgroundConfigPatchSchema.optional(),
     experimental: ExperimentalConfigPatchSchema.optional(),
diff --git a/packages/agent-core/src/config/toml.ts b/packages/agent-core/src/config/toml.ts
index 172e97cfc..79789c145 100644
--- a/packages/agent-core/src/config/toml.ts
+++ b/packages/agent-core/src/config/toml.ts
@@ -472,6 +472,7 @@ export function configToTomlData(config: KimiConfig): Record<string, unknown> {
     'defaultPlanMode',
     'mergeAllAvailableSkills',
     'extraSkillDirs',
+    'outputStyle',
     'telemetry',
   ];
   for (const key of scalarFields) {
diff --git a/packages/agent-core/src/output-style/builtin.ts b/packages/agent-core/src/output-style/builtin.ts
new file mode 100644
index 000000000..c41f03e7b
--- /dev/null
+++ b/packages/agent-core/src/output-style/builtin.ts
@@ -0,0 +1,11 @@
+import type { OutputStyle } from './types';
+export const BUILTIN_OUTPUT_STYLES: readonly OutputStyle[] = [
+  { name: 'concise', source: 'builtin', description: 'Terse, minimal-prose responses focused on the result.',
+    body: ['Respond as briefly as the task allows. Prefer the answer or the action over explanation.',
+      'Skip preamble, restating the question, and summaries unless explicitly asked.',
+      'Use short sentences and compact lists. Never pad. Correctness and completeness still come first.'].join('\n') },
+  { name: 'explanatory', source: 'builtin', description: 'Explains the reasoning and teaches as it works.',
+    body: ['As you work, briefly explain the reasoning behind notable decisions and trade-offs so the user learns from the process.',
+      'Call out alternatives you considered and why you rejected them, and surface non-obvious gotchas.',
+      'Keep explanations proportional — enough to teach, never so much that it buries the result.'].join('\n') },
+];
diff --git a/packages/agent-core/src/output-style/index.ts b/packages/agent-core/src/output-style/index.ts
new file mode 100644
index 000000000..01efe3414
--- /dev/null
+++ b/packages/agent-core/src/output-style/index.ts
@@ -0,0 +1,32 @@
+import { loadOutputStyles } from './loader';
+import type { OutputStyle } from './types';
+
+export type { OutputStyle, OutputStyleSource, ParsedOutputStyle } from './types';
+export { parseOutputStyle, OutputStyleParseError } from './parser';
+export { BUILTIN_OUTPUT_STYLES } from './builtin';
+export { loadOutputStyles } from './loader';
+export type { LoadOutputStylesOptions, OutputStylePathContext } from './loader';
+
+export function resolveOutputStyle(styles: readonly OutputStyle[], name: string | undefined): OutputStyle | undefined {
+  if (name === undefined || name.trim() === '') return undefined;
+  return styles.find((s) => s.name === name.trim());
+}
+
+export interface LoadConfiguredOutputStyleInput {
+  readonly name: string | undefined;
+  readonly userHomeDir: string;
+  readonly brandHomeDir?: string;
+  readonly workDir: string;
+  readonly onWarning?: (message: string, cause?: unknown) => void;
+}
+
+export async function loadConfiguredOutputStyleBody(
+  input: LoadConfiguredOutputStyleInput,
+): Promise<string | undefined> {
+  if (input.name === undefined || input.name.trim() === '') return undefined;
+  const styles = await loadOutputStyles({
+    paths: { userHomeDir: input.userHomeDir, brandHomeDir: input.brandHomeDir, workDir: input.workDir },
+    onWarning: input.onWarning,
+  });
+  return resolveOutputStyle(styles, input.name)?.body;
+}
diff --git a/packages/agent-core/src/output-style/loader.ts b/packages/agent-core/src/output-style/loader.ts
new file mode 100644
index 000000000..c465f33c1
--- /dev/null
+++ b/packages/agent-core/src/output-style/loader.ts
@@ -0,0 +1,57 @@
+import { promises as fs } from 'node:fs';
+import { dirname, join, resolve } from 'pathe';
+import { parseOutputStyle, OutputStyleParseError } from './parser';
+import { BUILTIN_OUTPUT_STYLES } from './builtin';
+import type { OutputStyle, OutputStyleSource } from './types';
+
+export interface OutputStylePathContext { readonly userHomeDir: string; readonly brandHomeDir?: string; readonly workDir: string; }
+export interface LoadOutputStylesOptions {
+  readonly paths: OutputStylePathContext;
+  readonly onWarning?: (message: string, cause?: unknown) => void;
+  readonly readdir?: (p: string) => Promise<readonly string[]>;
+  readonly readFile?: (p: string) => Promise<string>;
+  readonly isDir?: (p: string) => Promise<boolean>;
+}
+
+export async function loadOutputStyles(options: LoadOutputStylesOptions): Promise<readonly OutputStyle[]> {
+  const readdir = options.readdir ?? ((p) => fs.readdir(p));
+  const readFile = options.readFile ?? ((p) => fs.readFile(p, 'utf8'));
+  const isDir = options.isDir ?? (async (p) => { try { return (await fs.stat(p)).isDirectory(); } catch { return false; } });
+  const warn = options.onWarning ?? (() => {});
+  const { userHomeDir, workDir } = options.paths;
+  const brandHomeDir = options.paths.brandHomeDir ?? join(userHomeDir, '.kimi-code');
+  const projectRoot = await findProjectRoot(workDir);
+  const byName = new Map<string, OutputStyle>();
+  for (const s of BUILTIN_OUTPUT_STYLES) byName.set(s.name, s);
+  await scanDir(join(brandHomeDir, 'output-styles'), 'user');
+  await scanDir(join(projectRoot, '.kimi-code', 'output-styles'), 'project');
+  return [...byName.values()].toSorted((a, b) => a.name.localeCompare(b.name));
+
+  async function scanDir(dir: string, source: OutputStyleSource): Promise<void> {
+    if (!(await isDir(dir))) return;
+    let entries: readonly string[];
+    try { entries = [...(await readdir(dir))].toSorted(); }
+    catch (error) { warn(`Failed to read output-style directory ${dir}`, error); return; }
+    for (const entry of entries) {
+      if (!entry.endsWith('.md')) continue;
+      const file = join(dir, entry);
+      try {
+        const parsed = parseOutputStyle(await readFile(file), entry.slice(0, -'.md'.length));
+        byName.set(parsed.name, { ...parsed, source });
+      } catch (error) {
+        if (error instanceof OutputStyleParseError) warn(`Skipping invalid output style at ${file}: ${error.message}`, error);
+        else warn(`Skipping output style at ${file} due to unexpected error`, error);
+      }
+    }
+  }
+}
+
+async function findProjectRoot(workDir: string): Promise<string> {
+  let current = resolve(workDir);
+  while (true) {
+    try { await fs.stat(join(current, '.git')); return current; } catch { /* keep walking */ }
+    const parent = dirname(current);
+    if (parent === current) return resolve(workDir);
+    current = parent;
+  }
+}
diff --git a/packages/agent-core/src/output-style/parser.ts b/packages/agent-core/src/output-style/parser.ts
new file mode 100644
index 000000000..352e13158
--- /dev/null
+++ b/packages/agent-core/src/output-style/parser.ts
@@ -0,0 +1,33 @@
+import { FrontmatterError, parseFrontmatter } from '../skill/parser';
+import type { ParsedOutputStyle } from './types';
+
+export class OutputStyleParseError extends Error {
+  constructor(message: string, cause?: unknown) {
+    super(message);
+    this.name = 'OutputStyleParseError';
+    if (cause !== undefined) Object.defineProperty(this, 'cause', { value: cause, configurable: true });
+  }
+}
+
+export function parseOutputStyle(text: string, fallbackName: string): ParsedOutputStyle {
+  let parsed;
+  try { parsed = parseFrontmatter(text); }
+  catch (error) {
+    if (error instanceof FrontmatterError) throw new OutputStyleParseError(`Invalid frontmatter: ${error.message}`, error);
+    throw error;
+  }
+  const fm = isRecord(parsed.data) ? parsed.data : {};
+  const body = parsed.body.trim();
+  if (body === '') throw new OutputStyleParseError('Output style body is empty');
+  const name = nonEmptyString(fm['name']) ?? fallbackName;
+  const description = nonEmptyString(fm['description']) ?? firstLine(body) ?? 'No description provided.';
+  return { name, description, body };
+}
+
+function firstLine(body: string): string | undefined {
+  const line = body.split(/\r?\n/).map((l) => l.trim()).find((l) => l.length > 0);
+  if (line === undefined) return undefined;
+  return line.length > 240 ? `${line.slice(0, 239)}…` : line;
+}
+function nonEmptyString(value: unknown): string | undefined { return typeof value === 'string' && value.trim() !== '' ? value.trim() : undefined; }
+function isRecord(value: unknown): value is Record<string, unknown> { return typeof value === 'object' && value !== null && !Array.isArray(value); }
diff --git a/packages/agent-core/src/output-style/types.ts b/packages/agent-core/src/output-style/types.ts
new file mode 100644
index 000000000..7bae47abb
--- /dev/null
+++ b/packages/agent-core/src/output-style/types.ts
@@ -0,0 +1,3 @@
+export type OutputStyleSource = 'project' | 'user' | 'builtin';
+export interface OutputStyle { readonly name: string; readonly description: string; readonly body: string; readonly source: OutputStyleSource; }
+export interface ParsedOutputStyle { readonly name: string; readonly description: string; readonly body: string; }
diff --git a/packages/agent-core/src/profile/context.ts b/packages/agent-core/src/profile/context.ts
index 49d8d8105..d708785e9 100644
--- a/packages/agent-core/src/profile/context.ts
+++ b/packages/agent-core/src/profile/context.ts
@@ -1,8 +1,11 @@
+import { homedir } from 'node:os';
+
 import { dirname, join } from 'pathe';
 
 import type { Kaos } from '@moonshot-ai/kaos';
 
 import { listDirectory } from '../tools/support/list-directory';
+import { loadConfiguredOutputStyleBody } from '../output-style';
 import type { SystemPromptContext } from './types';
 
 const AGENTS_MD_MAX_BYTES = 32 * 1024;
@@ -11,17 +14,27 @@ const AGENTS_MD_TRUNCATION_MARKER =
 const S_IFMT = 0o170000;
 const S_IFREG = 0o100000;
 
-export type PreparedSystemPromptContext = Pick<SystemPromptContext, 'cwdListing' | 'agentsMd'>;
+export type PreparedSystemPromptContext = Pick<
+  SystemPromptContext,
+  'cwdListing' | 'agentsMd' | 'outputStyleBody'
+>;
 
 export async function prepareSystemPromptContext(
   kaos: Kaos,
   brandHome?: string,
+  outputStyleName?: string,
 ): Promise<PreparedSystemPromptContext> {
-  const [cwdListing, agentsMd] = await Promise.all([
+  const [cwdListing, agentsMd, outputStyleBody] = await Promise.all([
     listDirectory(kaos, undefined, { collapseHiddenDirs: true }),
     loadAgentsMd(kaos, brandHome),
+    loadConfiguredOutputStyleBody({
+      name: outputStyleName,
+      userHomeDir: homedir(),
+      brandHomeDir: brandHome,
+      workDir: kaos.getcwd(),
+    }),
   ]);
-  return { cwdListing, agentsMd };
+  return { cwdListing, agentsMd, outputStyleBody };
 }
 
 export async function loadAgentsMd(kaos: Kaos, brandHome?: string): Promise<string> {
diff --git a/packages/agent-core/src/profile/default/system.md b/packages/agent-core/src/profile/default/system.md
index d3b0084cc..56f0a21e5 100644
--- a/packages/agent-core/src/profile/default/system.md
+++ b/packages/agent-core/src/profile/default/system.md
@@ -116,6 +116,16 @@ The applicable `AGENTS.md` instructions are:
 ```````
 {{ KIMI_AGENTS_MD }}
 ```````
+{% if KIMI_OUTPUT_STYLE %}
+
+# Output Style
+
+The user selected a custom output style. Apply these response-style instructions on top of everything above. They govern tone, format, and verbosity only — they never override correctness, safety, or the task's actual requirements:
+
+```````
+{{ KIMI_OUTPUT_STYLE }}
+```````
+{% endif %}
 
 # Skills
 
diff --git a/packages/agent-core/src/profile/resolve.ts b/packages/agent-core/src/profile/resolve.ts
index 001f7d19f..9fed13a1f 100644
--- a/packages/agent-core/src/profile/resolve.ts
+++ b/packages/agent-core/src/profile/resolve.ts
@@ -162,6 +162,7 @@ function buildTemplateVars(
     KIMI_ADDITIONAL_DIRS_INFO: context.additionalDirsInfo ?? '',
     ROLE_ADDITIONAL:
       context.roleAdditional ?? promptVars['ROLE_ADDITIONAL'] ?? promptVars['roleAdditional'] ?? '',
+    KIMI_OUTPUT_STYLE: context.outputStyleBody ?? '',
   };
 }
 
diff --git a/packages/agent-core/src/profile/types.ts b/packages/agent-core/src/profile/types.ts
index 27d407c3b..0d3402a9d 100644
--- a/packages/agent-core/src/profile/types.ts
+++ b/packages/agent-core/src/profile/types.ts
@@ -42,6 +42,7 @@ export interface SystemPromptContext {
   readonly skills?: SkillRegistry | string;
   readonly additionalDirsInfo?: string;
   readonly roleAdditional?: string;
+  readonly outputStyleBody?: string;
 }
 
 export type SystemPromptRenderer = (context: SystemPromptContext) => string;
diff --git a/packages/agent-core/src/session/index.ts b/packages/agent-core/src/session/index.ts
index ca8c531a9..c6b570e54 100644
--- a/packages/agent-core/src/session/index.ts
+++ b/packages/agent-core/src/session/index.ts
@@ -407,6 +407,7 @@ export class Session {
     const context = await prepareSystemPromptContext(
       this.systemContextKaos(agent.kaos.getcwd()),
       this.options.kimiHomeDir,
+      this.options.config?.outputStyle,
     );
     agent.useProfile(profile, context);
   }
diff --git a/packages/agent-core/src/session/subagent-host.ts b/packages/agent-core/src/session/subagent-host.ts
index b47e1cd68..25e40af99 100644
--- a/packages/agent-core/src/session/subagent-host.ts
+++ b/packages/agent-core/src/session/subagent-host.ts
@@ -365,6 +365,7 @@ export class SessionSubagentHost {
     const context = await prepareSystemPromptContext(
       this.session.systemContextKaos(child.kaos.getcwd()),
       this.session.options.kimiHomeDir,
+      this.session.options.config?.outputStyle,
     );
     child.useProfile(profile, context);
     child.tools.inheritUserTools(parent.tools);
diff --git a/packages/agent-core/test/config/output-style-config.test.ts b/packages/agent-core/test/config/output-style-config.test.ts
new file mode 100644
index 000000000..a78f8d11f
--- /dev/null
+++ b/packages/agent-core/test/config/output-style-config.test.ts
@@ -0,0 +1,7 @@
+import { describe, expect, it } from 'vitest';
+import { KimiConfigSchema, KimiConfigPatchSchema } from '../../src/config/schema';
+describe('outputStyle config', () => {
+  it('accepts an outputStyle name', () => { expect(KimiConfigSchema.parse({ outputStyle: 'concise' }).outputStyle).toBe('concise'); });
+  it('is optional', () => { expect(KimiConfigSchema.parse({}).outputStyle).toBeUndefined(); });
+  it('is patchable', () => { expect(KimiConfigPatchSchema.parse({ outputStyle: 'explanatory' }).outputStyle).toBe('explanatory'); });
+});
diff --git a/packages/agent-core/test/config/output-style-writeback.test.ts b/packages/agent-core/test/config/output-style-writeback.test.ts
new file mode 100644
index 000000000..2903fecfb
--- /dev/null
+++ b/packages/agent-core/test/config/output-style-writeback.test.ts
@@ -0,0 +1,27 @@
+import { mkdtempSync } from 'node:fs';
+import { readFile, rm } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
+import { join } from 'pathe';
+import { afterEach, describe, expect, it } from 'vitest';
+
+import { parseConfigString, writeConfigFile } from '../../src/config';
+
+const tempDirs: string[] = [];
+afterEach(async () => {
+  for (const dir of tempDirs.splice(0)) await rm(dir, { recursive: true, force: true });
+});
+function makeTempDir(): string {
+  const dir = mkdtempSync(join(tmpdir(), 'kimi-os-cfg-'));
+  tempDirs.push(dir);
+  return dir;
+}
+
+describe('outputStyle config write-back', () => {
+  it('persists output_style through writeConfigFile and reparses it', async () => {
+    const configPath = join(makeTempDir(), 'config.toml');
+    await writeConfigFile(configPath, { providers: {}, outputStyle: 'concise' });
+    const text = await readFile(configPath, 'utf-8');
+    expect(text).toContain('output_style = "concise"');
+    expect(parseConfigString(text, configPath).outputStyle).toBe('concise');
+  });
+});
diff --git a/packages/agent-core/test/output-style/builtin.test.ts b/packages/agent-core/test/output-style/builtin.test.ts
new file mode 100644
index 000000000..793677a55
--- /dev/null
+++ b/packages/agent-core/test/output-style/builtin.test.ts
@@ -0,0 +1,12 @@
+import { describe, expect, it } from 'vitest';
+import { BUILTIN_OUTPUT_STYLES } from '../../src/output-style/builtin';
+describe('BUILTIN_OUTPUT_STYLES', () => {
+  it('ships concise and explanatory, all builtin-sourced with non-empty bodies', () => {
+    expect(BUILTIN_OUTPUT_STYLES.map((s) => s.name).toSorted()).toEqual(['concise', 'explanatory']);
+    for (const s of BUILTIN_OUTPUT_STYLES) {
+      expect(s.source).toBe('builtin');
+      expect(s.body.trim().length).toBeGreaterThan(0);
+      expect(s.description.trim().length).toBeGreaterThan(0);
+    }
+  });
+});
diff --git a/packages/agent-core/test/output-style/configured.test.ts b/packages/agent-core/test/output-style/configured.test.ts
new file mode 100644
index 000000000..83f79a072
--- /dev/null
+++ b/packages/agent-core/test/output-style/configured.test.ts
@@ -0,0 +1,30 @@
+import { mkdtemp, mkdir, writeFile, rm } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
+import path from 'node:path';
+import { afterEach, beforeEach, describe, expect, it } from 'vitest';
+import { loadConfiguredOutputStyleBody } from '../../src/output-style';
+
+let dir: string;
+beforeEach(async () => { dir = await mkdtemp(path.join(tmpdir(), 'osc-')); });
+afterEach(async () => { await rm(dir, { recursive: true, force: true }); });
+
+describe('loadConfiguredOutputStyleBody', () => {
+  it('returns undefined when no name is configured', async () => {
+    expect(await loadConfiguredOutputStyleBody({ name: undefined, userHomeDir: dir, workDir: dir })).toBeUndefined();
+    expect(await loadConfiguredOutputStyleBody({ name: '   ', userHomeDir: dir, workDir: dir })).toBeUndefined();
+  });
+  it('resolves a built-in style body by name', async () => {
+    const body = await loadConfiguredOutputStyleBody({ name: 'concise', userHomeDir: dir, workDir: dir });
+    expect(body).toContain('Respond as briefly');
+  });
+  it('returns undefined for an unknown style name', async () => {
+    expect(await loadConfiguredOutputStyleBody({ name: 'nope', userHomeDir: dir, workDir: dir })).toBeUndefined();
+  });
+  it('resolves a user-defined style that overrides a built-in', async () => {
+    const styleDir = path.join(dir, 'output-styles');
+    await mkdir(styleDir, { recursive: true });
+    await writeFile(path.join(styleDir, 'concise.md'), '---\nname: concise\n---\nMY OVERRIDE');
+    const body = await loadConfiguredOutputStyleBody({ name: 'concise', userHomeDir: dir, brandHomeDir: dir, workDir: dir });
+    expect(body).toBe('MY OVERRIDE');
+  });
+});
diff --git a/packages/agent-core/test/output-style/loader.test.ts b/packages/agent-core/test/output-style/loader.test.ts
new file mode 100644
index 000000000..bb9b75c9b
--- /dev/null
+++ b/packages/agent-core/test/output-style/loader.test.ts
@@ -0,0 +1,39 @@
+import { mkdtemp, mkdir, writeFile, rm } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
+import path from 'node:path';
+import { afterEach, beforeEach, describe, expect, it } from 'vitest';
+import { loadOutputStyles } from '../../src/output-style/loader';
+
+let dir: string;
+beforeEach(async () => { dir = await mkdtemp(path.join(tmpdir(), 'os-')); });
+afterEach(async () => { await rm(dir, { recursive: true, force: true }); });
+async function writeStyle(root: string, name: string, body: string) {
+  const d = path.join(root, 'output-styles');
+  await mkdir(d, { recursive: true });
+  await writeFile(path.join(d, `${name}.md`), `---\nname: ${name}\ndescription: ${name} desc\n---\n${body}\n`);
+}
+describe('loadOutputStyles', () => {
+  it('includes built-ins when no files exist', async () => {
+    const styles = await loadOutputStyles({ paths: { userHomeDir: dir, workDir: dir } });
+    expect(styles.map((s) => s.name).toSorted()).toEqual(['concise', 'explanatory']);
+  });
+  it('project overrides user overrides built-in by name', async () => {
+    const project = path.join(dir, 'proj'); const brand = path.join(dir, 'brand');
+    await mkdir(path.join(project, '.git'), { recursive: true });
+    await writeStyle(path.join(project, '.kimi-code'), 'concise', 'PROJECT body');
+    await writeStyle(brand, 'concise', 'USER body');
+    const styles = await loadOutputStyles({ paths: { userHomeDir: dir, brandHomeDir: brand, workDir: path.join(project, '.kimi-code') } });
+    const c = styles.find((s) => s.name === 'concise');
+    expect(c?.body).toBe('PROJECT body'); expect(c?.source).toBe('project');
+  });
+  it('skips invalid files but keeps the rest', async () => {
+    const brand = path.join(dir, 'brand');
+    await writeStyle(brand, 'good', 'ok body');
+    await mkdir(path.join(brand, 'output-styles'), { recursive: true });
+    await writeFile(path.join(brand, 'output-styles', 'bad.md'), '---\nname: "unterminated\n---\nx');
+    const warnings: string[] = [];
+    const styles = await loadOutputStyles({ paths: { userHomeDir: dir, brandHomeDir: brand, workDir: dir }, onWarning: (m) => warnings.push(m) });
+    expect(styles.find((s) => s.name === 'good')).toBeDefined();
+    expect(warnings.some((w) => w.includes('bad.md'))).toBe(true);
+  });
+});
diff --git a/packages/agent-core/test/output-style/parser.test.ts b/packages/agent-core/test/output-style/parser.test.ts
new file mode 100644
index 000000000..892c8b903
--- /dev/null
+++ b/packages/agent-core/test/output-style/parser.test.ts
@@ -0,0 +1,21 @@
+import { describe, expect, it } from 'vitest';
+import { OutputStyleParseError, parseOutputStyle } from '../../src/output-style/parser';
+
+describe('parseOutputStyle', () => {
+  it('reads name + description from frontmatter and trims body', () => {
+    const text = ['---', 'name: concise', 'description: Terse answers', '---', '', 'Be brief.', ''].join('\n');
+    expect(parseOutputStyle(text, 'fallback')).toEqual({ name: 'concise', description: 'Terse answers', body: 'Be brief.' });
+  });
+  it('falls back to filename and first body line when frontmatter omits them', () => {
+    const style = parseOutputStyle('Just instructions, no frontmatter.', 'my-style');
+    expect(style.name).toBe('my-style');
+    expect(style.description).toBe('Just instructions, no frontmatter.');
+    expect(style.body).toBe('Just instructions, no frontmatter.');
+  });
+  it('throws when the body is empty', () => {
+    expect(() => parseOutputStyle(['---', 'name: empty', '---', '', '   ', ''].join('\n'), 'empty')).toThrow(OutputStyleParseError);
+  });
+  it('throws OutputStyleParseError on invalid frontmatter YAML', () => {
+    expect(() => parseOutputStyle(['---', 'name: "unterminated', '---', 'body'].join('\n'), 'x')).toThrow(OutputStyleParseError);
+  });
+});
diff --git a/packages/agent-core/test/output-style/resolve.test.ts b/packages/agent-core/test/output-style/resolve.test.ts
new file mode 100644
index 000000000..fae613a17
--- /dev/null
+++ b/packages/agent-core/test/output-style/resolve.test.ts
@@ -0,0 +1,21 @@
+import { describe, expect, it } from 'vitest';
+import { resolveOutputStyle, type OutputStyle } from '../../src/output-style';
+
+const styles: readonly OutputStyle[] = [
+  { name: 'concise', description: 'd', body: 'b1', source: 'builtin' },
+  { name: 'explanatory', description: 'd', body: 'b2', source: 'user' },
+];
+
+describe('resolveOutputStyle', () => {
+  it('returns the matching style by name', () => {
+    expect(resolveOutputStyle(styles, 'explanatory')?.body).toBe('b2');
+  });
+  it('trims the name before matching', () => {
+    expect(resolveOutputStyle(styles, '  concise  ')?.name).toBe('concise');
+  });
+  it('returns undefined for unknown, empty, or undefined name', () => {
+    expect(resolveOutputStyle(styles, 'nope')).toBeUndefined();
+    expect(resolveOutputStyle(styles, '')).toBeUndefined();
+    expect(resolveOutputStyle(styles, undefined)).toBeUndefined();
+  });
+});
diff --git a/packages/agent-core/test/output-style/system-prompt.test.ts b/packages/agent-core/test/output-style/system-prompt.test.ts
new file mode 100644
index 000000000..3821ab30f
--- /dev/null
+++ b/packages/agent-core/test/output-style/system-prompt.test.ts
@@ -0,0 +1,31 @@
+import { describe, expect, it } from 'vitest';
+import { DEFAULT_AGENT_PROFILES } from '../../src/profile';
+
+const baseContext = {
+  osEnv: {
+    osKind: 'macOS',
+    osArch: 'arm64',
+    osVersion: '0',
+    shellName: 'bash',
+    shellPath: '/bin/bash',
+  },
+  cwd: '/workspace',
+  now: '2026-05-09T00:00:00.000Z',
+  cwdListing: '',
+  agentsMd: '',
+  skills: '',
+} as const;
+
+describe('output style system prompt plumbing', () => {
+  it('injects outputStyleBody into the rendered system prompt', () => {
+    const context = { ...baseContext, outputStyleBody: 'BE_TERSE_MARKER' };
+    const prompt = DEFAULT_AGENT_PROFILES['agent']?.systemPrompt(context) ?? '';
+    expect(prompt).toContain('BE_TERSE_MARKER');
+    expect(prompt).toContain('# Output Style');
+  });
+
+  it('omits the Output Style section when outputStyleBody is absent', () => {
+    const prompt = DEFAULT_AGENT_PROFILES['agent']?.systemPrompt(baseContext) ?? '';
+    expect(prompt).not.toContain('# Output Style');
+  });
+});