diff --git a/src/config/unified-config-loader.ts b/src/config/unified-config-loader.ts
index 9f3935b2..17d28742 100644
--- a/src/config/unified-config-loader.ts
+++ b/src/config/unified-config-loader.ts
@@ -18,7 +18,9 @@ import {
   DEFAULT_GLOBAL_ENV,
   DEFAULT_CLIPROXY_SERVER_CONFIG,
   DEFAULT_QUOTA_MANAGEMENT_CONFIG,
+  DEFAULT_THINKING_CONFIG,
   GlobalEnvConfig,
+  ThinkingConfig,
 } from './unified-config-types';
 import { isUnifiedConfigEnabled } from './feature-flags';
 
@@ -242,6 +244,20 @@ function mergeWithDefaults(partial: Partial<UnifiedConfig>): UnifiedConfig {
           DEFAULT_QUOTA_MANAGEMENT_CONFIG.manual.tier_lock,
       },
     },
+    // Thinking config - auto/manual/off control for reasoning budget
+    thinking: {
+      mode: partial.thinking?.mode ?? DEFAULT_THINKING_CONFIG.mode,
+      override: partial.thinking?.override,
+      tier_defaults: {
+        opus: partial.thinking?.tier_defaults?.opus ?? DEFAULT_THINKING_CONFIG.tier_defaults.opus,
+        sonnet:
+          partial.thinking?.tier_defaults?.sonnet ?? DEFAULT_THINKING_CONFIG.tier_defaults.sonnet,
+        haiku:
+          partial.thinking?.tier_defaults?.haiku ?? DEFAULT_THINKING_CONFIG.tier_defaults.haiku,
+      },
+      provider_overrides: partial.thinking?.provider_overrides,
+      show_warnings: partial.thinking?.show_warnings ?? DEFAULT_THINKING_CONFIG.show_warnings,
+    },
   };
 }
 
@@ -575,3 +591,23 @@ export function getGlobalEnvConfig(): GlobalEnvConfig {
     env: config.global_env?.env ?? { ...DEFAULT_GLOBAL_ENV },
   };
 }
+
+/**
+ * Get thinking configuration.
+ * Returns defaults if not configured.
+ */
+export function getThinkingConfig(): ThinkingConfig {
+  const config = loadOrCreateUnifiedConfig();
+  return {
+    mode: config.thinking?.mode ?? DEFAULT_THINKING_CONFIG.mode,
+    override: config.thinking?.override,
+    tier_defaults: {
+      opus: config.thinking?.tier_defaults?.opus ?? DEFAULT_THINKING_CONFIG.tier_defaults.opus,
+      sonnet:
+        config.thinking?.tier_defaults?.sonnet ?? DEFAULT_THINKING_CONFIG.tier_defaults.sonnet,
+      haiku: config.thinking?.tier_defaults?.haiku ?? DEFAULT_THINKING_CONFIG.tier_defaults.haiku,
+    },
+    provider_overrides: config.thinking?.provider_overrides,
+    show_warnings: config.thinking?.show_warnings ?? DEFAULT_THINKING_CONFIG.show_warnings,
+  };
+}
diff --git a/src/config/unified-config-types.ts b/src/config/unified-config-types.ts
index e5eec79b..ecb3e636 100644
--- a/src/config/unified-config-types.ts
+++ b/src/config/unified-config-types.ts
@@ -17,8 +17,9 @@
  * Version 5 = Remote proxy configuration (connect to remote CLIProxyAPI)
  * Version 6 = Customizable auth tokens (API key and management secret)
  * Version 7 = Quota management for hybrid auto+manual account control
+ * Version 8 = Thinking/reasoning budget configuration
  */
-export const UNIFIED_CONFIG_VERSION = 7;
+export const UNIFIED_CONFIG_VERSION = 8;
 
 /**
  * Account configuration (formerly in profiles.json).
@@ -424,6 +425,66 @@ export const DEFAULT_QUOTA_MANAGEMENT_CONFIG: QuotaManagementConfig = {
   manual: { ...DEFAULT_MANUAL_QUOTA_CONFIG },
 };
 
+// ============================================================================
+// THINKING CONFIGURATION (v8+)
+// ============================================================================
+
+/**
+ * Thinking mode for auto/manual/off control.
+ * - auto: Apply tier-based defaults (opus→high, sonnet→medium, haiku→low)
+ * - off: Disable thinking entirely
+ * - manual: Use explicit override value
+ */
+export type ThinkingMode = 'auto' | 'off' | 'manual';
+
+/**
+ * Tier-to-thinking level defaults.
+ * Maps Claude tier names to thinking level names.
+ */
+export interface ThinkingTierDefaults {
+  /** Thinking level for opus tier (default: 'high') */
+  opus: string;
+  /** Thinking level for sonnet tier (default: 'medium') */
+  sonnet: string;
+  /** Thinking level for haiku tier (default: 'low') */
+  haiku: string;
+}
+
+/**
+ * Thinking configuration section.
+ * Controls thinking/reasoning budget injection for CLIProxy providers.
+ */
+export interface ThinkingConfig {
+  /** Thinking mode (default: 'auto') */
+  mode: ThinkingMode;
+  /** Manual override value (level name or budget number) */
+  override?: string | number;
+  /** Tier-to-level mapping */
+  tier_defaults: ThinkingTierDefaults;
+  /** Per-provider overrides (e.g., { gemini: { opus: 'high' } }) */
+  provider_overrides?: Record<string, Partial<ThinkingTierDefaults>>;
+  /** Show warning when values are clamped (default: true) */
+  show_warnings?: boolean;
+}
+
+/**
+ * Default thinking tier defaults.
+ */
+export const DEFAULT_THINKING_TIER_DEFAULTS: ThinkingTierDefaults = {
+  opus: 'high',
+  sonnet: 'medium',
+  haiku: 'low',
+};
+
+/**
+ * Default thinking configuration.
+ */
+export const DEFAULT_THINKING_CONFIG: ThinkingConfig = {
+  mode: 'auto',
+  tier_defaults: { ...DEFAULT_THINKING_TIER_DEFAULTS },
+  show_warnings: true,
+};
+
 /**
  * Main unified configuration structure.
  * Stored in ~/.ccs/config.yaml
@@ -451,6 +512,8 @@ export interface UnifiedConfig {
   cliproxy_server?: CliproxyServerConfig;
   /** Quota management configuration (v7+) */
   quota_management?: QuotaManagementConfig;
+  /** Thinking/reasoning budget configuration (v8+) */
+  thinking?: ThinkingConfig;
 }
 
 /**
@@ -540,6 +603,7 @@ export function createEmptyUnifiedConfig(): UnifiedConfig {
     copilot: { ...DEFAULT_COPILOT_CONFIG },
     cliproxy_server: { ...DEFAULT_CLIPROXY_SERVER_CONFIG },
     quota_management: { ...DEFAULT_QUOTA_MANAGEMENT_CONFIG },
+    thinking: { ...DEFAULT_THINKING_CONFIG },
   };
 }