diff --git a/src/extension.ts b/src/extension.ts
index eb35936..6637a34 100644
--- a/src/extension.ts
+++ b/src/extension.ts
@@ -16,7 +16,7 @@ import { HarnessService, HARNESS_TARGETS, HARNESS_VERSION } from './services/har
 import { SelectorsService } from './services/selectorsService';
 import { LegacyTagCleanupService } from './services/legacyTagCleanupService';
 import { LogicalModelService } from './services/logicalModelService';
-import { MigrationService } from './services/migrationService';
+import { MigrationService, migrateLegacySemanticDir } from './services/migrationService';
 import { YmlParserService } from './services/ymlParserService';
 import { ModelLibraryTreeProvider, type ModelLibraryNode } from './providers/ModelLibraryTreeProvider';
 import { DOMAIN_EDITOR_VIEW_TYPE, hasOpenDomainCanvas, saveAllAndReload } from './services/recoveryService';
@@ -186,6 +186,16 @@ export async function activate(context: vscode.ExtensionContext): Promise<void>
   const config = vscode.workspace.getConfiguration('dbtSemantic');
   const semanticDir = config.get<string>('semanticDir', '.erd-studio');
 
+  // v0.6.44 moved the default data directory from erd-studio/ to .erd-studio/.
+  // Rename legacy folders in place before any service reads from disk so
+  // existing projects keep working without intervention.
+  if (migrateLegacySemanticDir(workspaceRoot, semanticDir)) {
+    void vscode.window.showInformationMessage(
+      'ERD Studio: your erd-studio/ folder was renamed to .erd-studio/ (the new default location). ' +
+        'Commit the rename so collaborators stay in sync.',
+    );
+  }
+
   const layerService = new LayerService(workspaceRoot, semanticDir);
   const domainService = new DomainService(layerService);
   const logicalModelService = new LogicalModelService(workspaceRoot, semanticDir);
diff --git a/src/services/migrationService.ts b/src/services/migrationService.ts
index 5559a46..dca07b9 100644
--- a/src/services/migrationService.ts
+++ b/src/services/migrationService.ts
@@ -46,6 +46,64 @@ export interface MigrationResult {
   mergeConflicts: string[];
 }
 
+// ---------------------------------------------------------------------------
+// Legacy directory migration (erd-studio/ → .erd-studio/)
+// ---------------------------------------------------------------------------
+
+const DEFAULT_SEMANTIC_DIR = '.erd-studio';
+const LEGACY_SEMANTIC_DIR = 'erd-studio';
+
+/** Files/dirs whose presence identifies a folder as an ERD Studio data dir. */
+const ERD_DIR_MARKERS = ['layers.json', 'logical-models', 'templates'];
+
+/**
+ * Returns the absolute path of a legacy erd-studio/ data directory that
+ * should be renamed to .erd-studio/, or null when no migration applies.
+ *
+ * Migration applies only when ALL of:
+ *   - the effective semanticDir is the default '.erd-studio' (a custom
+ *     setting means the user manages the location themselves)
+ *   - '.erd-studio' does not already exist
+ *   - 'erd-studio' exists, is a directory, and looks like an ERD data dir
+ *     (has a known marker, or a layer subdirectory containing .json files)
+ */
+export function findLegacySemanticDir(
+  workspaceRoot: string,
+  semanticDir: string,
+): string | null {
+  if (semanticDir !== DEFAULT_SEMANTIC_DIR) return null;
+  if (fs.existsSync(path.join(workspaceRoot, semanticDir))) return null;
+
+  const legacy = path.join(workspaceRoot, LEGACY_SEMANTIC_DIR);
+  if (!fs.existsSync(legacy) || !fs.statSync(legacy).isDirectory()) return null;
+
+  const hasMarker = ERD_DIR_MARKERS.some((m) => fs.existsSync(path.join(legacy, m)));
+  if (hasMarker) return legacy;
+
+  const hasLayerWithDomains = fs.readdirSync(legacy).some((entry) => {
+    const sub = path.join(legacy, entry);
+    return (
+      fs.statSync(sub).isDirectory() &&
+      fs.readdirSync(sub).some((f) => f.endsWith('.json'))
+    );
+  });
+  return hasLayerWithDomains ? legacy : null;
+}
+
+/**
+ * Rename a legacy erd-studio/ directory to .erd-studio/ in place.
+ * Returns true when a rename happened.
+ */
+export function migrateLegacySemanticDir(
+  workspaceRoot: string,
+  semanticDir: string,
+): boolean {
+  const legacy = findLegacySemanticDir(workspaceRoot, semanticDir);
+  if (!legacy) return false;
+  fs.renameSync(legacy, path.join(workspaceRoot, semanticDir));
+  return true;
+}
+
 // ---------------------------------------------------------------------------
 // Service
 // ---------------------------------------------------------------------------
diff --git a/test/unit/migrationService.test.ts b/test/unit/migrationService.test.ts
new file mode 100644
index 0000000..d306aaf
--- /dev/null
+++ b/test/unit/migrationService.test.ts
@@ -0,0 +1,124 @@
+import * as fs from 'fs';
+import * as os from 'os';
+import * as path from 'path';
+import { afterEach, beforeEach, describe, expect, it } from 'vitest';
+
+import {
+  findLegacySemanticDir,
+  migrateLegacySemanticDir,
+} from '../../src/services/migrationService';
+
+describe('legacy semantic dir migration (erd-studio/ → .erd-studio/)', () => {
+  let workspaceRoot: string;
+
+  beforeEach(() => {
+    workspaceRoot = fs.mkdtempSync(path.join(os.tmpdir(), 'erd-migration-'));
+  });
+
+  afterEach(() => {
+    fs.rmSync(workspaceRoot, { recursive: true, force: true });
+  });
+
+  function makeLegacyDir(contents: 'layers' | 'logical-models' | 'templates' | 'layer-domains' | 'empty' | 'unrelated') {
+    const legacy = path.join(workspaceRoot, 'erd-studio');
+    fs.mkdirSync(legacy);
+    switch (contents) {
+      case 'layers':
+        fs.writeFileSync(path.join(legacy, 'layers.json'), '{"layers":[]}');
+        break;
+      case 'logical-models':
+        fs.mkdirSync(path.join(legacy, 'logical-models'));
+        break;
+      case 'templates':
+        fs.mkdirSync(path.join(legacy, 'templates'));
+        break;
+      case 'layer-domains':
+        fs.mkdirSync(path.join(legacy, 'silver'));
+        fs.writeFileSync(path.join(legacy, 'silver', 'orders.json'), '{}');
+        break;
+      case 'unrelated':
+        fs.writeFileSync(path.join(legacy, 'notes.txt'), 'not an erd dir');
+        break;
+      case 'empty':
+        break;
+    }
+    return legacy;
+  }
+
+  describe('findLegacySemanticDir', () => {
+    it.each(['layers', 'logical-models', 'templates', 'layer-domains'] as const)(
+      'detects a legacy dir identified by %s',
+      (marker) => {
+        const legacy = makeLegacyDir(marker);
+        expect(findLegacySemanticDir(workspaceRoot, '.erd-studio')).toBe(legacy);
+      },
+    );
+
+    it('returns null when no legacy dir exists', () => {
+      expect(findLegacySemanticDir(workspaceRoot, '.erd-studio')).toBeNull();
+    });
+
+    it('returns null when .erd-studio already exists', () => {
+      makeLegacyDir('layers');
+      fs.mkdirSync(path.join(workspaceRoot, '.erd-studio'));
+      expect(findLegacySemanticDir(workspaceRoot, '.erd-studio')).toBeNull();
+    });
+
+    it('returns null when semanticDir is customised', () => {
+      makeLegacyDir('layers');
+      expect(findLegacySemanticDir(workspaceRoot, 'erd-studio')).toBeNull();
+      expect(findLegacySemanticDir(workspaceRoot, 'custom/dir')).toBeNull();
+    });
+
+    it('returns null for a folder that does not look like an ERD data dir', () => {
+      makeLegacyDir('unrelated');
+      expect(findLegacySemanticDir(workspaceRoot, '.erd-studio')).toBeNull();
+    });
+
+    it('returns null for an empty erd-studio folder', () => {
+      makeLegacyDir('empty');
+      expect(findLegacySemanticDir(workspaceRoot, '.erd-studio')).toBeNull();
+    });
+
+    it('returns null when erd-studio is a file, not a directory', () => {
+      fs.writeFileSync(path.join(workspaceRoot, 'erd-studio'), 'file');
+      expect(findLegacySemanticDir(workspaceRoot, '.erd-studio')).toBeNull();
+    });
+  });
+
+  describe('migrateLegacySemanticDir', () => {
+    it('renames the legacy dir and preserves contents', () => {
+      makeLegacyDir('layer-domains');
+      fs.writeFileSync(
+        path.join(workspaceRoot, 'erd-studio', 'layers.json'),
+        '{"layers":[]}',
+      );
+
+      const renamed = migrateLegacySemanticDir(workspaceRoot, '.erd-studio');
+
+      expect(renamed).toBe(true);
+      expect(fs.existsSync(path.join(workspaceRoot, 'erd-studio'))).toBe(false);
+      expect(
+        fs.readFileSync(
+          path.join(workspaceRoot, '.erd-studio', 'silver', 'orders.json'),
+          'utf-8',
+        ),
+      ).toBe('{}');
+      expect(
+        fs.existsSync(path.join(workspaceRoot, '.erd-studio', 'layers.json')),
+      ).toBe(true);
+    });
+
+    it('is a no-op when nothing to migrate', () => {
+      expect(migrateLegacySemanticDir(workspaceRoot, '.erd-studio')).toBe(false);
+    });
+
+    it('is a no-op when .erd-studio already exists alongside a legacy dir', () => {
+      makeLegacyDir('layers');
+      fs.mkdirSync(path.join(workspaceRoot, '.erd-studio'));
+
+      expect(migrateLegacySemanticDir(workspaceRoot, '.erd-studio')).toBe(false);
+      expect(fs.existsSync(path.join(workspaceRoot, 'erd-studio'))).toBe(true);
+    });
+  });
+});