From 19252c55776633f6778ab0871860cab0323afa44 Mon Sep 17 00:00:00 2001
From: FBumann <117816358+FBumann@users.noreply.github.com>
Date: Sat, 13 Jun 2026 18:26:19 +0200
Subject: [PATCH 1/2] feat(io): stamp linopy version into netCDF export

Record the writing linopy version under the ``_linopy_version`` dataset
attribute in ``to_netcdf``. This is provenance today and a future key for
format-compatibility branching on read. Files written by older versions
(no attribute) keep reading unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 doc/release_notes.rst |  2 ++
 linopy/io.py          |  4 ++++
 test/test_io.py       | 26 ++++++++++++++++++++++++++
 3 files changed, 32 insertions(+)

diff --git a/doc/release_notes.rst b/doc/release_notes.rst
index 9b1ecbd8..81a4b562 100644
--- a/doc/release_notes.rst
+++ b/doc/release_notes.rst
@@ -4,6 +4,8 @@ Release Notes
 Upcoming Version
 ----------------
 
+* ``Model.to_netcdf`` now records the writing linopy version in the ``_linopy_version`` dataset attribute. Files written by older versions (without the attribute) continue to read unchanged.
+
 Version 0.8.0
 -------------
 
diff --git a/linopy/io.py b/linopy/io.py
index 1c4714c4..220a230a 100644
--- a/linopy/io.py
+++ b/linopy/io.py
@@ -12,6 +12,7 @@
 import time
 import warnings
 from collections.abc import Callable, Iterable
+from importlib.metadata import version
 from io import BufferedWriter
 from pathlib import Path
 from tempfile import TemporaryDirectory
@@ -37,6 +38,8 @@
 
 logger = logging.getLogger(__name__)
 
+NETCDF_VERSION_ATTR = "_linopy_version"
+
 
 ufunc_kwargs = dict(vectorize=True)
 concat_kwargs = dict(dim=CONCAT_DIM, coords="minimal")
@@ -971,6 +974,7 @@ def with_prefix(ds: xr.Dataset, prefix: str) -> xr.Dataset:
     scalars = {k: getattr(m, k) for k in m.scalar_attrs}
     ds = xr.merge(vars + cons + obj + params, combine_attrs="drop_conflicts")
     ds = ds.assign_attrs(scalars)
+    ds.attrs[NETCDF_VERSION_ATTR] = version("linopy")
     if m._relaxed_registry:
         ds.attrs["_relaxed_registry"] = json.dumps(m._relaxed_registry)
     if m._piecewise_formulations:
diff --git a/test/test_io.py b/test/test_io.py
index fba65aab..b108926f 100644
--- a/test/test_io.py
+++ b/test/test_io.py
@@ -221,6 +221,32 @@ def test_read_netcdf_with_multiindex_legacy_list_attr(
     assert_model_equal(m, read_netcdf(fn_legacy))
 
 
+def test_model_to_netcdf_stamps_version(model: Model, tmp_path: Path) -> None:
+    from importlib.metadata import version
+
+    from linopy.io import NETCDF_VERSION_ATTR
+
+    fn = tmp_path / "test.nc"
+    model.to_netcdf(fn)
+
+    ds = xr.load_dataset(fn)
+    assert ds.attrs[NETCDF_VERSION_ATTR] == version("linopy")
+
+
+def test_read_netcdf_without_version_stamp(model: Model, tmp_path: Path) -> None:
+    from linopy.io import NETCDF_VERSION_ATTR
+
+    fn = tmp_path / "test.nc"
+    model.to_netcdf(fn)
+
+    ds = xr.load_dataset(fn).load()
+    del ds.attrs[NETCDF_VERSION_ATTR]
+    fn_legacy = tmp_path / "legacy.nc"
+    ds.to_netcdf(fn_legacy)
+
+    assert_model_equal(model, read_netcdf(fn_legacy))
+
+
 @pytest.mark.skipif("gurobi" not in available_solvers, reason="Gurobipy not installed")
 def test_to_file_lp(model: Model, tmp_path: Path) -> None:
     import gurobipy

From 428227cc66880fd5d4cef08181b6904f2ec2c9ab Mon Sep 17 00:00:00 2001
From: FBumann <117816358+FBumann@users.noreply.github.com>
Date: Sat, 13 Jun 2026 18:32:01 +0200
Subject: [PATCH 2/2] test(io): drop tautological version-stamp assertion

The equal-to-__version__ test mirrored the assignment one-to-one. Keep only
the backward-compat test that an unstamped (pre-versioning) file still reads.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 test/test_io.py | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/test/test_io.py b/test/test_io.py
index b108926f..dd614c5e 100644
--- a/test/test_io.py
+++ b/test/test_io.py
@@ -221,18 +221,6 @@ def test_read_netcdf_with_multiindex_legacy_list_attr(
     assert_model_equal(m, read_netcdf(fn_legacy))
 
 
-def test_model_to_netcdf_stamps_version(model: Model, tmp_path: Path) -> None:
-    from importlib.metadata import version
-
-    from linopy.io import NETCDF_VERSION_ATTR
-
-    fn = tmp_path / "test.nc"
-    model.to_netcdf(fn)
-
-    ds = xr.load_dataset(fn)
-    assert ds.attrs[NETCDF_VERSION_ATTR] == version("linopy")
-
-
 def test_read_netcdf_without_version_stamp(model: Model, tmp_path: Path) -> None:
     from linopy.io import NETCDF_VERSION_ATTR