diff --git a/pkgs/development/python-modules/h5py/default.nix b/pkgs/development/python-modules/h5py/default.nix
index b0ab2fc32af4..0adb77a037ef 100644
--- a/pkgs/development/python-modules/h5py/default.nix
+++ b/pkgs/development/python-modules/h5py/default.nix
@@ -79,6 +79,11 @@ buildPythonPackage rec {
 
   pythonImportsCheck = [ "h5py" ];
 
+  passthru = {
+    # To evaluate more easily *Support flags of it from within Python Packages.
+    inherit hdf5;
+  };
+
   meta = {
     changelog = "https://github.com/h5py/h5py/blob/${version}/docs/whatsnew/${lib.versions.majorMinor version}.rst";
     description = "Pythonic interface to the HDF5 binary data format";
diff --git a/pkgs/development/python-modules/xarray/default.nix b/pkgs/development/python-modules/xarray/default.nix
index 823d1bcada2e..6bc6e731ce2b 100644
--- a/pkgs/development/python-modules/xarray/default.nix
+++ b/pkgs/development/python-modules/xarray/default.nix
@@ -33,18 +33,21 @@
   # tests
   pytest-asyncio,
   pytestCheckHook,
+  h5py,
 }:
 
-buildPythonPackage rec {
+buildPythonPackage (finalAttrs: {
   pname = "xarray";
-  version = "2026.02.0";
+  version = "2026.04.0";
   pyproject = true;
+  # Needed mainly for pytestFlags with spaces
+  __structuredAttrs = true;
 
   src = fetchFromGitHub {
     owner = "pydata";
     repo = "xarray";
-    tag = "v${version}";
-    hash = "sha256-g1cKI0Et3RToWOxn+bELtT5jAaB8e1N+k9doCU+OgfY=";
+    tag = "v${finalAttrs.version}";
+    hash = "sha256-BsgL+Xo9fTMLLdz5AfScnKGuBa76cE85LuUzB4ZNLiY=";
   };
 
   postPatch = ''
@@ -63,7 +66,7 @@ buildPythonPackage rec {
     pandas
   ];
 
-  optional-dependencies = lib.fix (self: {
+  optional-dependencies = {
     accel = [
       bottleneck
       # flox
@@ -90,25 +93,36 @@ buildPythonPackage rec {
       # nc-time-axis
       seaborn
     ];
-    complete = with self; accel ++ io ++ etc ++ parallel ++ viz;
-  });
+    complete =
+      with finalAttrs.finalPackage.passthru.optional-dependencies;
+      accel ++ io ++ etc ++ parallel ++ viz;
+  };
 
   nativeCheckInputs = [
     pytest-asyncio
     pytestCheckHook
-    scipy
-  ];
-
-  disabledTestPaths = [
-    # https://github.com/pydata/xarray/issues/11183
-    "xarray/tests/test_dataarray.py::TestDataArray::test_curvefit_helpers" # Failed: DID NOT RAISE <class 'ValueError'>
-    "xarray/tests/test_variable.py::TestIndexVariable::test_concat_periods" # ValueError: Could not convert <xarray.IndexVariable 't' (t: 5)> Size: 40B
+  ]
+  # Besides scipy, these are not strictly needed for the tests, but adding all
+  # of these optional-dependencies extends the amount of tests from ~17k to
+  # ~21k.
+  ++ finalAttrs.finalPackage.optional-dependencies.io
+  ++ finalAttrs.finalPackage.optional-dependencies.accel
+  ++ finalAttrs.finalPackage.optional-dependencies.etc
+  ++ finalAttrs.finalPackage.optional-dependencies.parallel
+  # Not adding optional-dependencies.viz because adding cartopy causes infinite
+  # recursion, and doesn't cause more tests to be collected.
+  ;
+  pytestFlags = lib.optionals (!h5py.hdf5.szipSupport) [
+    "-k"
+    # Our h5py is built with hdf5 that is built without szip support, so we
+    # skip these tests
+    "not szip"
   ];
 
   pythonImportsCheck = [ "xarray" ];
 
   meta = {
-    changelog = "https://github.com/pydata/xarray/blob/${src.tag}/doc/whats-new.rst";
+    changelog = "https://github.com/pydata/xarray/blob/${finalAttrs.src.tag}/doc/whats-new.rst";
     description = "N-D labeled arrays and datasets in Python";
     homepage = "https://github.com/pydata/xarray";
     license = lib.licenses.asl20;
@@ -116,4 +130,4 @@ buildPythonPackage rec {
       doronbehar
     ];
   };
-}
+})