C-Achard · Oct 23, 2026 · Oct 23, 2026
diff --git a/deeplabcut/utils/auxfun_multianimal.py b/deeplabcut/utils/auxfun_multianimal.py
@@ -211,8 +211,7 @@ def LoadFullMultiAnimalData(dataname):
             data = pickle.load(handle)
     except (pickle.UnpicklingError, FileNotFoundError):
         data = shelve.open(data_file, flag="r")
-    with metadata_file.open("rb") as handle:
-        metadata = pickle.load(handle)
+    metadata = auxiliaryfunctions.read_pickle(metadata_file)
     return data, metadata
 
 

diff --git a/deeplabcut/utils/auxiliaryfunctions.py b/deeplabcut/utils/auxiliaryfunctions.py
@@ -24,7 +24,7 @@
 import os
 import pickle
 from collections.abc import Sequence
-from pathlib import Path
+from pathlib import Path, PurePosixPath, PureWindowsPath
 
 import pandas as pd
 
@@ -139,10 +139,28 @@ def attempt_to_make_folder(foldername, recursive=False):
         foldername.mkdir(exist_ok=True, parents=True)
 
 
+_FOREIGN_PATH_NAME, _FOREIGN_PATH_TYPE = (
+    ("PosixPath", PurePosixPath) if os.name == "nt" else ("WindowsPath", PureWindowsPath)
+)
+
+
+class _PortableUnpickler(pickle.Unpickler):
+    """Unpickler loading paths pickled on another OS as pure paths."""
+
+    def find_class(self, module, name):
+        # Python 3.13+ pickles paths from ``pathlib._local``
+        if module in ("pathlib", "pathlib._local") and name == _FOREIGN_PATH_NAME:
+            return _FOREIGN_PATH_TYPE
+        return super().find_class(module, name)
+
+
 def read_pickle(filename):
-    """Read the pickle file."""
+    """Read the pickle file.
+
+    Paths pickled on another OS are loaded as ``PurePosixPath`` or ``PureWindowsPath``.
+    """
     with Path(filename).open("rb") as handle:
-        return pickle.load(handle)
+        return _PortableUnpickler(handle).load()
 
 
 def write_pickle(filename, data):

diff --git a/tests/test_auxiliaryfunctions.py b/tests/test_auxiliaryfunctions.py
@@ -8,7 +8,8 @@
 #
 # Licensed under GNU Lesser General Public License v3.0
 #
-from pathlib import Path
+import os
+from pathlib import Path, PurePosixPath, PureWindowsPath
 from unittest.mock import patch
 
 import pytest
@@ -349,3 +350,25 @@ def test_project_path_updated_when_moved(self, tmp_path):
 
         expected = project_dir.absolute()
         assert cfg["project_path"] == expected
+
+
+def _write_path_pickle(path: Path, module: str, cls_name: str) -> Path:
+    # Protocol 0 pickle of ``{"project_path": <module>.<cls_name>("a", "b")}``; written by hand
+    # because a concrete path of the other OS cannot be created to pickle it
+    path.write_bytes(f"(dVproject_path\nc{module}\n{cls_name}\n(Va\nVb\ntRs.".encode())
+    return path
+
+
+@pytest.mark.parametrize("module", ["pathlib", "pathlib._local"])
+def test_read_pickle_loads_foreign_paths_as_pure(tmp_path, module):
+    """Paths pickled on another OS load as pure paths instead of raising (#3562)."""
+    foreign_name, pure_type = ("PosixPath", PurePosixPath) if os.name == "nt" else ("WindowsPath", PureWindowsPath)
+    data = auxiliaryfunctions.read_pickle(_write_path_pickle(tmp_path / "meta.pickle", module, foreign_name))
+    assert type(data["project_path"]) is pure_type
+    assert data["project_path"].parts == ("a", "b")
+
+
+def test_read_pickle_keeps_native_paths(tmp_path):
+    native_type = type(Path())
+    data = auxiliaryfunctions.read_pickle(_write_path_pickle(tmp_path / "meta.pickle", "pathlib", native_type.__name__))
+    assert type(data["project_path"]) is native_type