diff --git a/src/config/unified-config-loader.ts b/src/config/unified-config-loader.ts
index 505928f3..292ec9e5 100644
--- a/src/config/unified-config-loader.ts
+++ b/src/config/unified-config-loader.ts
@@ -90,12 +90,39 @@ export function loadUnifiedConfig(): UnifiedConfig | null {
   }
 }
 
+/**
+ * Merge partial config with defaults.
+ * Preserves existing data while filling in missing sections.
+ */
+function mergeWithDefaults(partial: Partial<UnifiedConfig>): UnifiedConfig {
+  const defaults = createEmptyUnifiedConfig();
+  return {
+    version: partial.version ?? defaults.version,
+    default: partial.default ?? defaults.default,
+    accounts: partial.accounts ?? defaults.accounts,
+    profiles: partial.profiles ?? defaults.profiles,
+    cliproxy: {
+      oauth_accounts: partial.cliproxy?.oauth_accounts ?? defaults.cliproxy.oauth_accounts,
+      providers: defaults.cliproxy.providers, // Always use defaults for providers
+      variants: partial.cliproxy?.variants ?? defaults.cliproxy.variants,
+    },
+    preferences: {
+      ...defaults.preferences,
+      ...partial.preferences,
+    },
+  };
+}
+
 /**
  * Load config, preferring YAML if available, falling back to creating empty config.
+ * Merges with defaults to ensure all sections exist.
  */
 export function loadOrCreateUnifiedConfig(): UnifiedConfig {
   const existing = loadUnifiedConfig();
-  if (existing) return existing;
+  if (existing) {
+    // Merge with defaults to fill any missing sections
+    return mergeWithDefaults(existing);
+  }
 
   // Create empty config
   const config = createEmptyUnifiedConfig();
diff --git a/src/config/unified-config-types.ts b/src/config/unified-config-types.ts
index e41cc4a1..ed313298 100644
--- a/src/config/unified-config-types.ts
+++ b/src/config/unified-config-types.ts
@@ -151,17 +151,15 @@ export function createEmptySecretsConfig(): SecretsConfig {
 
 /**
  * Type guard for UnifiedConfig.
+ * Relaxed validation: accepts configs with version >= 1 and any subset of sections.
+ * Missing sections will be filled with defaults during merge.
  */
 export function isUnifiedConfig(obj: unknown): obj is UnifiedConfig {
   if (typeof obj !== 'object' || obj === null) return false;
   const config = obj as Record<string, unknown>;
-  return (
-    typeof config.version === 'number' &&
-    config.version === UNIFIED_CONFIG_VERSION &&
-    typeof config.accounts === 'object' &&
-    typeof config.profiles === 'object' &&
-    typeof config.cliproxy === 'object'
-  );
+  // Only require version to be a number >= 1 (allow future versions)
+  // Sections are optional - will be merged with defaults in loadOrCreateUnifiedConfig
+  return typeof config.version === 'number' && config.version >= 1;
 }
 
 /**
diff --git a/tests/unit/unified-config.test.ts b/tests/unit/unified-config.test.ts
index 3ad80b22..b345bd34 100644
--- a/tests/unit/unified-config.test.ts
+++ b/tests/unit/unified-config.test.ts
@@ -124,14 +124,23 @@ describe('unified-config-types', () => {
       expect(isUnifiedConfig(null)).toBe(false);
     });
 
-    it('should return false for wrong version', () => {
+    it('should return true for older version (relaxed validation)', () => {
+      // Fix for issue #82: Relaxed validation accepts version >= 1
+      // to prevent profile loss when loading partially valid configs
       const config = { ...createEmptyUnifiedConfig(), version: 1 };
-      expect(isUnifiedConfig(config)).toBe(false);
+      expect(isUnifiedConfig(config)).toBe(true);
     });
 
-    it('should return false for missing fields', () => {
-      expect(isUnifiedConfig({ version: 2 })).toBe(false);
-      expect(isUnifiedConfig({ version: 2, accounts: {} })).toBe(false);
+    it('should return true for partial configs (relaxed validation)', () => {
+      // Fix for issue #82: Relaxed validation accepts partial configs
+      // Missing sections are merged with defaults in loadOrCreateUnifiedConfig
+      expect(isUnifiedConfig({ version: 2 })).toBe(true);
+      expect(isUnifiedConfig({ version: 2, accounts: {} })).toBe(true);
+    });
+
+    it('should return false for version < 1', () => {
+      expect(isUnifiedConfig({ version: 0 })).toBe(false);
+      expect(isUnifiedConfig({ version: -1 })).toBe(false);
     });
   });