diff --git a/scripts/model_compiler.py b/scripts/model_compiler.py
index 4f3b658f5..72ce0ec06 100644
--- a/scripts/model_compiler.py
+++ b/scripts/model_compiler.py
@@ -301,6 +301,57 @@ def sha256_file(path: Path) -> str:
   return digest.hexdigest()
 
 
+def _read_protobuf_varint(source) -> int:
+  value = 0
+  for shift in range(0, 70, 7):
+    byte = source.read(1)
+    if not byte:
+      raise ValueError("unexpected end of file while reading protobuf varint")
+    value |= (byte[0] & 0x7F) << shift
+    if not byte[0] & 0x80:
+      return value
+  raise ValueError("protobuf varint is too long")
+
+
+def validate_onnx_source(path: Path) -> None:
+  """Validate the top-level ONNX protobuf without materializing model weights."""
+  size = path.stat().st_size
+  if size == 0:
+    raise ValueError(f"ONNX source is empty: {path}")
+
+  with open(path, "rb") as source:
+    if source.read(128).startswith(b"version https://git-lfs.github.com/spec/v1"):
+      raise ValueError(f"ONNX source is a Git LFS pointer, not model data: {path}")
+    source.seek(0)
+
+    while source.tell() < size:
+      tag = _read_protobuf_varint(source)
+      field, wire_type = tag >> 3, tag & 0x07
+      if field == 7:  # ModelProto.graph
+        if wire_type != 2:
+          raise ValueError(f"ONNX graph has invalid protobuf wire type {wire_type}: {path}")
+        graph_size = _read_protobuf_varint(source)
+        remaining = size - source.tell()
+        if graph_size <= 0:
+          raise ValueError(f"ONNX graph is empty: {path}")
+        if graph_size > remaining:
+          raise ValueError(f"ONNX source is truncated: graph needs {graph_size} bytes but only {remaining} remain: {path}")
+        return
+
+      if wire_type == 0:
+        _read_protobuf_varint(source)
+      elif wire_type == 1:
+        source.seek(8, os.SEEK_CUR)
+      elif wire_type == 2:
+        source.seek(_read_protobuf_varint(source), os.SEEK_CUR)
+      elif wire_type == 5:
+        source.seek(4, os.SEEK_CUR)
+      else:
+        raise ValueError(f"ONNX source has invalid protobuf wire type {wire_type}: {path}")
+
+  raise ValueError(f"ONNX ModelProto has no graph: {path}")
+
+
 def multipart_output_paths(artifact: Path, output_dir: Path | None = None) -> list[Path]:
   output_dir = output_dir or artifact.parent
   return [
@@ -552,6 +603,11 @@ def main() -> int:
     raise SystemExit(f"No staged ONNX files found for {model_key} in {args.input_dir}")
 
   input_format = select_input_format(args.input_format, files)
+  _, source_args = driving_compile_args(files, input_format)
+  for option, source in zip(source_args[::2], source_args[1::2], strict=True):
+    source_path = Path(source)
+    validate_onnx_source(source_path)
+    print(f"  source {option.removeprefix('--')}: {source_path} ({source_path.stat().st_size} bytes)")
   version = infer_model_version(model_key, args.version)
   if not version and input_format == "supercombo":
     version = "v15"
diff --git a/selfdrive/modeld/compile_modeld.py b/selfdrive/modeld/compile_modeld.py
index 50f3df792..4dacdcd15 100644
--- a/selfdrive/modeld/compile_modeld.py
+++ b/selfdrive/modeld/compile_modeld.py
@@ -476,6 +476,9 @@ def _parse_size(value):
 def read_file_chunked_to_disk(path):
   from openpilot.common.file_chunker import open_file_chunked
 
+  if os.path.isfile(path):
+    return os.fspath(path)
+
   temporary_path = f"{path}.unchunked"
   try:
     with open(temporary_path, "wb") as output, open_file_chunked(path) as source:
diff --git a/starpilot/assets/tests/test_model_pipeline.py b/starpilot/assets/tests/test_model_pipeline.py
index 71e6afa94..3448438c4 100644
--- a/starpilot/assets/tests/test_model_pipeline.py
+++ b/starpilot/assets/tests/test_model_pipeline.py
@@ -79,7 +79,15 @@ def test_requested_model_id_uses_only_staged_source(tmp_path):
   }
 
 
-def test_fat_onnx_is_streamed_to_disk(tmp_path, monkeypatch):
+def test_regular_fat_onnx_is_parsed_in_place(tmp_path, monkeypatch):
+  source = tmp_path / "big_driving_supercombo.onnx"
+  source.write_bytes(b"model")
+  monkeypatch.setattr(file_chunker, "open_file_chunked", lambda _: (_ for _ in ()).throw(AssertionError("must not copy")))
+
+  assert compile_modeld.read_file_chunked_to_disk(source) == str(source)
+
+
+def test_chunked_fat_onnx_is_streamed_to_disk(tmp_path, monkeypatch):
   payload = b"fat model" * 1024
 
   class StreamingOnly(io.BytesIO):
@@ -97,6 +105,30 @@ def test_fat_onnx_is_streamed_to_disk(tmp_path, monkeypatch):
     Path(staged).unlink(missing_ok=True)
 
 
+def test_onnx_preflight_accepts_graph_without_reading_weights(tmp_path):
+  source = tmp_path / "model.onnx"
+  source.write_bytes(b"\x08\x09\x3a\x02\x12\x00")
+
+  model_compiler.validate_onnx_source(source)
+
+
+def test_onnx_preflight_rejects_empty_truncated_and_lfs_sources(tmp_path):
+  empty = tmp_path / "empty.onnx"
+  empty.touch()
+  truncated = tmp_path / "truncated.onnx"
+  truncated.write_bytes(b"\x3a\x08bad")
+  pointer = tmp_path / "pointer.onnx"
+  pointer.write_text("version https://git-lfs.github.com/spec/v1\n")
+
+  for source, message in ((empty, "empty"), (truncated, "truncated"), (pointer, "Git LFS pointer")):
+    try:
+      model_compiler.validate_onnx_source(source)
+    except ValueError as error:
+      assert message in str(error)
+    else:
+      raise AssertionError(f"{source} should have failed validation")
+
+
 def test_dropbox_urls_are_direct_downloads():
   url = "https://www.dropbox.com/scl/fi/id/model.pkl?rlkey=key&st=value&dl=0"
   normalized = download_functions.normalize_download_url(url)