diff --git a/py/services/model_lifecycle_service.py b/py/services/model_lifecycle_service.py
index 9aa87b04..1416768d 100644
--- a/py/services/model_lifecycle_service.py
+++ b/py/services/model_lifecycle_service.py
@@ -236,10 +236,20 @@ class ModelLifecycleService:
     def _get_multipart_ext(filename: str) -> str:
         """Return the extension for files with compound suffixes."""
 
-        parts = filename.split(".")
-        if len(parts) == 3:
-            return "." + ".".join(parts[-2:])
-        if len(parts) >= 4:
-            return "." + ".".join(parts[-3:])
-        return os.path.splitext(filename)[1]
+        known_suffixes = [
+            ".metadata.json.bak",
+            ".metadata.json",
+            ".safetensors",
+            *PREVIEW_EXTENSIONS,
+        ]
 
+        for suffix in sorted(known_suffixes, key=len, reverse=True):
+            if filename.endswith(suffix):
+                return suffix
+
+        basename = os.path.basename(filename)
+        dot_index = basename.find(".")
+        if dot_index != -1:
+            return basename[dot_index:]
+
+        return os.path.splitext(basename)[1]
diff --git a/tests/services/test_model_lifecycle_service.py b/tests/services/test_model_lifecycle_service.py
new file mode 100644
index 00000000..e96f8236
--- /dev/null
+++ b/tests/services/test_model_lifecycle_service.py
@@ -0,0 +1,83 @@
+import json
+from pathlib import Path
+
+import pytest
+
+from py.services.model_lifecycle_service import ModelLifecycleService
+from py.utils.metadata_manager import MetadataManager
+
+
+class DummyScanner:
+    def __init__(self):
+        self.calls = []
+        self.model_type = "checkpoint"
+
+    async def update_single_model_cache(self, old_path, new_path, metadata):
+        self.calls.append((old_path, new_path, metadata))
+
+
+class PassthroughMetadataManager:
+    def __init__(self):
+        self.saved_payloads = []
+
+    async def save_metadata(self, path: str, metadata):
+        self.saved_payloads.append((path, metadata.copy()))
+        await MetadataManager.save_metadata(path, metadata)
+
+
+@pytest.mark.asyncio
+async def test_rename_model_preserves_compound_extensions(tmp_path: Path):
+    old_name = "Qwen-Image-Edit-2509-Lightning-8steps-V1.0-bf16.0-bf16"
+    new_name = f"{old_name}-testing"
+
+    model_path = tmp_path / f"{old_name}.safetensors"
+    model_path.write_bytes(b"lora")
+
+    preview_path = tmp_path / f"{old_name}.preview.webp"
+    preview_path.write_bytes(b"preview")
+
+    metadata_path = tmp_path / f"{old_name}.metadata.json"
+    metadata_payload = {
+        "file_name": old_name,
+        "file_path": model_path.as_posix(),
+        "preview_url": preview_path.as_posix(),
+    }
+    metadata_path.write_text(json.dumps(metadata_payload))
+
+    async def metadata_loader(path: str):
+        with open(path, "r", encoding="utf-8") as handle:
+            return json.load(handle)
+
+    scanner = DummyScanner()
+    metadata_manager = PassthroughMetadataManager()
+    service = ModelLifecycleService(
+        scanner=scanner,
+        metadata_manager=metadata_manager,
+        metadata_loader=metadata_loader,
+    )
+
+    result = await service.rename_model(
+        file_path=model_path.as_posix(),
+        new_file_name=new_name,
+    )
+
+    expected_main = tmp_path / f"{new_name}.safetensors"
+    expected_metadata = tmp_path / f"{new_name}.metadata.json"
+    expected_preview = tmp_path / f"{new_name}.preview.webp"
+
+    assert expected_main.exists()
+    assert not model_path.exists()
+    assert result["new_file_path"].endswith(f"{new_name}.safetensors")
+    assert expected_preview.exists()
+    assert not preview_path.exists()
+
+    saved_metadata = json.loads(expected_metadata.read_text())
+    assert saved_metadata["file_name"] == new_name
+    assert saved_metadata["file_path"].endswith(f"{new_name}.safetensors")
+    assert saved_metadata["preview_url"].endswith(f"{new_name}.preview.webp")
+
+    assert scanner.calls
+    old_call_path, new_call_path, payload = scanner.calls[0]
+    assert old_call_path.endswith(f"{old_name}.safetensors")
+    assert new_call_path.endswith(f"{new_name}.safetensors")
+    assert payload["file_name"] == new_name