diff --git a/docs/source/reference/geotiff_release_contract.md b/docs/source/reference/geotiff_release_contract.md
index 69063af23..0938c1c9b 100644
--- a/docs/source/reference/geotiff_release_contract.md
+++ b/docs/source/reference/geotiff_release_contract.md
@@ -106,7 +106,7 @@ category. The `Key` column matches the runtime key.
 | `writer.bigtiff` | advanced | `bigtiff=True` (or auto-promotion above 4 GiB) writes BigTIFF magic, 8-byte offsets, and 20-byte IFD entries. |
 | `writer.bigtiff_cog` | advanced | BigTIFF plus COG. Tracked separately because the combination has its own external-interop surface. |
 | `writer.gpu` | experimental | GPU write path. |
-| `writer.gdal_metadata_xml` | experimental | `attrs['gdal_metadata_xml']` is escaped before serialisation. |
+| `writer.gdal_metadata_xml` | experimental | `attrs['gdal_metadata_xml']` is escaped before serialisation. A dict `attrs['gdal_metadata']` rides the same gate: writers build the XML from it, so a fresh DataArray carrying it also requires `allow_experimental_codecs=True` (#3320). |
 | `writer.extra_tags` | experimental | Pass-through of TIFF tags outside the structured set via `attrs['extra_tags']`. |
 | `writer.pack` | experimental | `pack=True` on `to_geotiff`; inverse of `reader.unpack`. Re-applies the recorded scale/offset, restores the integer source dtype, and fills NaN back to the nodata sentinel. Tracked at the same tier as `reader.unpack` (#3112, #3114). |
 
diff --git a/xrspatial/geotiff/_attrs.py b/xrspatial/geotiff/_attrs.py
index b20d18331..47faa2515 100644
--- a/xrspatial/geotiff/_attrs.py
+++ b/xrspatial/geotiff/_attrs.py
@@ -531,6 +531,11 @@ def _validate_write_rich_tag_optin(
     triggered: list[str] = []
     if attrs.get('gdal_metadata_xml') is not None:
         triggered.append("attrs['gdal_metadata_xml']")
+    # ``_extract_rich_tags`` only builds GDAL XML from ``gdal_metadata``
+    # when it is a dict (and ``gdal_metadata_xml`` is absent); a non-dict
+    # value is ignored by the writer, so it does not need gating.
+    if isinstance(attrs.get('gdal_metadata'), dict):
+        triggered.append("attrs['gdal_metadata']")
     if attrs.get('extra_tags') is not None:
         triggered.append("attrs['extra_tags']")
     if gdal_metadata_xml_kwarg is not None:
diff --git a/xrspatial/geotiff/tests/attrs/test_contract.py b/xrspatial/geotiff/tests/attrs/test_contract.py
index 67a0d6210..1be15b548 100644
--- a/xrspatial/geotiff/tests/attrs/test_contract.py
+++ b/xrspatial/geotiff/tests/attrs/test_contract.py
@@ -347,6 +347,49 @@ def test_canonical_keys_present_per_backend(tmp_path, opener, label):
     )
 
 
+def _make_gdal_metadata_da():
+    """Fresh DataArray (no contract marker) carrying only a dict
+    ``gdal_metadata``. The writer turns this into on-disk GDAL XML, so it
+    must trip the experimental rich-tag gate (#3320)."""
+    data = np.arange(4, dtype=np.float32).reshape(2, 2)
+    return xr.DataArray(
+        data, dims=('y', 'x'),
+        coords={'y': [240.0, 230.0], 'x': [100.0, 110.0]},
+        attrs={'crs': 4326, 'gdal_metadata': {'AREA_OR_POINT': 'Area'}},
+    )
+
+
+def test_gdal_metadata_dict_requires_optin_3320(tmp_path):
+    """A fresh DataArray whose only rich-tag attr is a dict
+    ``gdal_metadata`` writes GDAL XML to disk, so ``to_geotiff`` must
+    reject it without ``allow_experimental_codecs`` and accept it with
+    the flag (#3320)."""
+    da = _make_gdal_metadata_da()
+    rejected = str(tmp_path / 'gdal_metadata_optin_3320_rejected.tif')
+    with pytest.raises(ValueError, match=r"attrs\['gdal_metadata'\]"):
+        to_geotiff(da, rejected)
+    assert not os.path.exists(rejected)
+
+    accepted = str(tmp_path / 'gdal_metadata_optin_3320_accepted.tif')
+    to_geotiff(da, accepted, allow_experimental_codecs=True)
+    assert os.path.exists(accepted)
+
+
+def test_gdal_metadata_dict_roundtrip_writes_flag_free_3320(tmp_path):
+    """A read-back DataArray carries the contract marker, so writing its
+    ``gdal_metadata`` back is the canonical round-trip and stays
+    flag-free even without the opt-in (#3320)."""
+    da = _make_gdal_metadata_da()
+    src = str(tmp_path / 'gdal_metadata_roundtrip_3320_src.tif')
+    to_geotiff(da, src, allow_experimental_codecs=True)
+
+    rd = open_geotiff(src)
+    assert '_xrspatial_geotiff_contract' in rd.attrs
+    out = str(tmp_path / 'gdal_metadata_roundtrip_3320_out.tif')
+    to_geotiff(rd, out)
+    assert os.path.exists(out)
+
+
 # ``raster_type`` lives outside the shared fixture because the canonical
 # default ('area') is encoded as *absence* in attrs. The two branches
 # need different fixtures.
diff --git a/xrspatial/geotiff/tests/gpu/test_writer.py b/xrspatial/geotiff/tests/gpu/test_writer.py
index 8341b70d3..ac93edba5 100644
--- a/xrspatial/geotiff/tests/gpu/test_writer.py
+++ b/xrspatial/geotiff/tests/gpu/test_writer.py
@@ -301,7 +301,9 @@ def test_gdal_metadata_round_trips_via_gpu_writer(tmp_path):
                                  'CUSTOM_KEY': 'val_1563'}},
     )
     out = str(tmp_path / 'gdal_meta_1563.tif')
-    _write_geotiff_gpu(da_gpu, out, compression='none')
+    # gdal_metadata dict is an experimental rich-tag write (#3320).
+    _write_geotiff_gpu(da_gpu, out, compression='none',
+                       allow_experimental_codecs=True)
 
     rd = open_geotiff(out)
     meta = rd.attrs.get('gdal_metadata') or {}
diff --git a/xrspatial/geotiff/tests/read/test_mask_and_scale_dtype_parity_3066.py b/xrspatial/geotiff/tests/read/test_mask_and_scale_dtype_parity_3066.py
index 402798304..5d1cb70e5 100644
--- a/xrspatial/geotiff/tests/read/test_mask_and_scale_dtype_parity_3066.py
+++ b/xrspatial/geotiff/tests/read/test_mask_and_scale_dtype_parity_3066.py
@@ -23,12 +23,15 @@ def _write(path, data, *, nodata=None, scale=None, offset=None):
             "SCALE": str(scale if scale is not None else 1.0),
             "OFFSET": str(offset if offset is not None else 0.0),
         }
+    # gdal_metadata SCALE/OFFSET dict on a fresh array is an experimental
+    # rich-tag write (#3320).
     to_geotiff(
         xr.DataArray(
             data, dims=("y", "x"),
             coords={"y": np.arange(h, 0, -1) - 0.5, "x": np.arange(w) + 0.5},
             attrs=attrs),
-        path)
+        path,
+        allow_experimental_codecs="gdal_metadata" in attrs)
     return path
 
 
diff --git a/xrspatial/geotiff/tests/read/test_rioxarray_compat_2961.py b/xrspatial/geotiff/tests/read/test_rioxarray_compat_2961.py
index 603bc20b5..8f3266c74 100644
--- a/xrspatial/geotiff/tests/read/test_rioxarray_compat_2961.py
+++ b/xrspatial/geotiff/tests/read/test_rioxarray_compat_2961.py
@@ -48,7 +48,9 @@ def _scale_offset_tiff(path, scale=2.0, offset=10.0, sentinel=255):
             "gdal_metadata": {"SCALE": str(scale), "OFFSET": str(offset)},
         },
     )
-    to_geotiff(da, path)
+    # gdal_metadata dict on a fresh array is an experimental rich-tag
+    # write (#3320).
+    to_geotiff(da, path, allow_experimental_codecs=True)
     return path
 
 
@@ -261,7 +263,9 @@ def _malformed_scale_tiff(path, scale="abc", offset="0"):
             "gdal_metadata": {"SCALE": scale, "OFFSET": offset},
         },
     )
-    to_geotiff(da, path)
+    # gdal_metadata dict on a fresh array is an experimental rich-tag
+    # write (#3320).
+    to_geotiff(da, path, allow_experimental_codecs=True)
     return path
 
 
@@ -486,7 +490,9 @@ def _per_band_scale_tiff(path, scales, offsets):
         },
         attrs={"crs": 4326, "gdal_metadata": meta},
     )
-    to_geotiff(da, path)
+    # gdal_metadata dict on a fresh array is an experimental rich-tag
+    # write (#3320).
+    to_geotiff(da, path, allow_experimental_codecs=True)
     return path
 
 
diff --git a/xrspatial/geotiff/tests/read/test_scale_zero_3104.py b/xrspatial/geotiff/tests/read/test_scale_zero_3104.py
index e992fd295..cff62ef7c 100644
--- a/xrspatial/geotiff/tests/read/test_scale_zero_3104.py
+++ b/xrspatial/geotiff/tests/read/test_scale_zero_3104.py
@@ -38,7 +38,9 @@ def _scale_tiff(path, scale, offset="0", nodata=None):
         coords={"y": [1.5, 0.5], "x": [0.5, 1.5, 2.5]},
         attrs=attrs,
     )
-    to_geotiff(da, path)
+    # gdal_metadata dict on a fresh array is an experimental rich-tag
+    # write (#3320).
+    to_geotiff(da, path, allow_experimental_codecs=True)
     return path
 
 
diff --git a/xrspatial/geotiff/tests/release_gates/test_features.py b/xrspatial/geotiff/tests/release_gates/test_features.py
index 0ad8d5b46..1e471e5e6 100644
--- a/xrspatial/geotiff/tests/release_gates/test_features.py
+++ b/xrspatial/geotiff/tests/release_gates/test_features.py
@@ -1519,7 +1519,8 @@ def test_dataarray_attrs_round_trip(self, tmp_path):
             attrs={'gdal_metadata': meta},
         )
         path = str(tmp_path / 'da_meta.tif')
-        to_geotiff(da, path, compression='none')
+        # gdal_metadata dict is an experimental rich-tag write (#3320).
+        to_geotiff(da, path, compression='none', allow_experimental_codecs=True)
 
         result = open_geotiff(path)
         assert result.attrs['gdal_metadata']['Source'] == 'test'
diff --git a/xrspatial/geotiff/tests/unit/test_safe_xml.py b/xrspatial/geotiff/tests/unit/test_safe_xml.py
index 12290072d..d5d3bdc73 100644
--- a/xrspatial/geotiff/tests/unit/test_safe_xml.py
+++ b/xrspatial/geotiff/tests/unit/test_safe_xml.py
@@ -116,7 +116,8 @@ def test_to_geotiff_special_chars_round_trip(self, tmp_path):
         }
 
         path = tmp_path / "meta.tif"
-        to_geotiff(da, str(path))
+        # gdal_metadata dict is an experimental rich-tag write (#3320).
+        to_geotiff(da, str(path), allow_experimental_codecs=True)
 
         opened = open_geotiff(str(path))
         round_tripped = opened.attrs.get("gdal_metadata")
diff --git a/xrspatial/geotiff/tests/unit/test_signatures.py b/xrspatial/geotiff/tests/unit/test_signatures.py
index 73eb4c0f4..832523eb2 100644
--- a/xrspatial/geotiff/tests/unit/test_signatures.py
+++ b/xrspatial/geotiff/tests/unit/test_signatures.py
@@ -762,11 +762,48 @@ def test_validate_write_rich_tag_optin_rejects_extra_tags():
         )
 
 
+def test_validate_write_rich_tag_optin_rejects_gdal_metadata_dict():
+    """A dict ``attrs['gdal_metadata']`` is written to disk as XML by
+    ``_extract_rich_tags``; it must trip the same gate (#3320).
+    """
+    with pytest.raises(ValueError, match=r"attrs\['gdal_metadata'\]"):
+        _validate_write_rich_tag_optin(
+            {'gdal_metadata': {'AREA_OR_POINT': 'Area'}},
+            allow_experimental_codecs=False,
+        )
+
+
+def test_validate_write_rich_tag_optin_names_both_xml_and_gdal_metadata():
+    """When both ``gdal_metadata_xml`` and a dict ``gdal_metadata`` are
+    present without the opt-in, the rejection names both attrs (#3320)."""
+    with pytest.raises(ValueError) as exc:
+        _validate_write_rich_tag_optin(
+            {'gdal_metadata_xml': '<GDALMetadata/>',
+             'gdal_metadata': {'AREA_OR_POINT': 'Area'}},
+            allow_experimental_codecs=False,
+        )
+    msg = str(exc.value)
+    assert "attrs['gdal_metadata_xml']" in msg
+    assert "attrs['gdal_metadata']" in msg
+
+
+def test_validate_write_rich_tag_optin_ignores_non_dict_gdal_metadata():
+    """Only a dict ``gdal_metadata`` builds XML in ``_extract_rich_tags``;
+    a non-dict value is ignored by the writer, so the gate stays quiet
+    (#3320).
+    """
+    _validate_write_rich_tag_optin(
+        {'gdal_metadata': 'not-a-dict'},
+        allow_experimental_codecs=False,
+    )
+
+
 def test_validate_write_rich_tag_optin_accepts_with_flag():
-    """``allow_experimental_codecs=True`` accepts both rich-tag attrs."""
+    """``allow_experimental_codecs=True`` accepts all rich-tag attrs."""
     _validate_write_rich_tag_optin(
         {'gdal_metadata_xml': '<GDALMetadata/>',
-         'extra_tags': [(700, 1, 0, b'')]},
+         'extra_tags': [(700, 1, 0, b'')],
+         'gdal_metadata': {'AREA_OR_POINT': 'Area'}},
         allow_experimental_codecs=True,
     )
 
@@ -780,6 +817,7 @@ def test_validate_write_rich_tag_optin_exempts_round_trip():
     _validate_write_rich_tag_optin(
         {'gdal_metadata_xml': '<GDALMetadata/>',
          'extra_tags': [(700, 1, 0, b'')],
+         'gdal_metadata': {'AREA_OR_POINT': 'Area'},
          '_xrspatial_geotiff_contract': 2},
         allow_experimental_codecs=False,
     )
diff --git a/xrspatial/geotiff/tests/vrt/test_metadata.py b/xrspatial/geotiff/tests/vrt/test_metadata.py
index 0181a4bd6..765141bef 100644
--- a/xrspatial/geotiff/tests/vrt/test_metadata.py
+++ b/xrspatial/geotiff/tests/vrt/test_metadata.py
@@ -831,7 +831,8 @@ class TestVrtTiledMetadataParity:
     def test_nodatavals_alias_propagates_to_tiles(self, tmp_path):
         da = _tiled_metadata_make_rioxarray_style()
         vrt = str(tmp_path / 'nodatavals.vrt')
-        to_geotiff(da, vrt, tile_size=16)
+        # gdal_metadata dict is an experimental rich-tag write (#3320).
+        to_geotiff(da, vrt, tile_size=16, allow_experimental_codecs=True)
         tile_da = open_geotiff(_tiled_metadata_first_tile_path(vrt))
         assert tile_da.attrs.get('nodata') == -9999.0
 
@@ -847,7 +848,7 @@ def test_fill_value_alias_propagates_to_tiles(self, tmp_path):
     def test_gdal_metadata_propagates_to_tiles(self, tmp_path):
         da = _tiled_metadata_make_rioxarray_style()
         vrt = str(tmp_path / 'gdal_meta.vrt')
-        to_geotiff(da, vrt, tile_size=16)
+        to_geotiff(da, vrt, tile_size=16, allow_experimental_codecs=True)
         tile_da = open_geotiff(_tiled_metadata_first_tile_path(vrt))
         gm = tile_da.attrs.get('gdal_metadata')
         assert gm == {'AREA_OR_POINT': 'Area', 'foo': 'bar'}
@@ -855,7 +856,7 @@ def test_gdal_metadata_propagates_to_tiles(self, tmp_path):
     def test_resolution_tags_propagate_to_tiles(self, tmp_path):
         da = _tiled_metadata_make_rioxarray_style()
         vrt = str(tmp_path / 'resolution.vrt')
-        to_geotiff(da, vrt, tile_size=16)
+        to_geotiff(da, vrt, tile_size=16, allow_experimental_codecs=True)
         tile_da = open_geotiff(_tiled_metadata_first_tile_path(vrt))
         assert tile_da.attrs.get('x_resolution') == 96.0
         assert tile_da.attrs.get('y_resolution') == 96.0
@@ -864,7 +865,7 @@ def test_resolution_tags_propagate_to_tiles(self, tmp_path):
     def test_raster_type_point_propagates_to_tiles(self, tmp_path):
         da = _tiled_metadata_make_rioxarray_style()
         vrt = str(tmp_path / 'point.vrt')
-        to_geotiff(da, vrt, tile_size=16)
+        to_geotiff(da, vrt, tile_size=16, allow_experimental_codecs=True)
         tile_da = open_geotiff(_tiled_metadata_first_tile_path(vrt))
         assert tile_da.attrs.get('raster_type') == 'point'
 
@@ -873,8 +874,8 @@ def test_tif_vs_vrt_tile_metadata_parity(self, tmp_path):
         da = _tiled_metadata_make_rioxarray_style()
         tif_path = str(tmp_path / 'parity.tif')
         vrt_path = str(tmp_path / 'parity.vrt')
-        to_geotiff(da, tif_path, tile_size=16)
-        to_geotiff(da, vrt_path, tile_size=16)
+        to_geotiff(da, tif_path, tile_size=16, allow_experimental_codecs=True)
+        to_geotiff(da, vrt_path, tile_size=16, allow_experimental_codecs=True)
         tif_da = open_geotiff(tif_path)
         tile_da = open_geotiff(_tiled_metadata_first_tile_path(vrt_path))
         keys = ('nodata', 'gdal_metadata', 'raster_type', 'x_resolution', 'y_resolution', 'resolution_unit')  # noqa: E501
@@ -934,7 +935,8 @@ def test_nodatavals_alias_dask(self, tmp_path):
         da_np = xr.DataArray(arr, dims=('y', 'x'), coords={'y': np.arange(8.0), 'x': np.arange(8.0)}, attrs={'nodatavals': (-9999.0,), 'crs': 4326, 'gdal_metadata': {'k': 'v'}})  # noqa: E501
         da = xr.DataArray(dska.from_array(arr, chunks=4), dims=da_np.dims, coords=da_np.coords, attrs=da_np.attrs)  # noqa: E501
         vrt = str(tmp_path / 'dask.vrt')
-        to_geotiff(da, vrt, tile_size=16)
+        # gdal_metadata dict is an experimental rich-tag write (#3320).
+        to_geotiff(da, vrt, tile_size=16, allow_experimental_codecs=True)
         tile_da = open_geotiff(_tiled_metadata_first_tile_path(vrt))
         assert tile_da.attrs.get('nodata') == -9999.0
         assert tile_da.attrs.get('gdal_metadata') == {'k': 'v'}
diff --git a/xrspatial/geotiff/tests/write/test_pack_3064.py b/xrspatial/geotiff/tests/write/test_pack_3064.py
index a27ddd3dd..e594137fb 100644
--- a/xrspatial/geotiff/tests/write/test_pack_3064.py
+++ b/xrspatial/geotiff/tests/write/test_pack_3064.py
@@ -41,7 +41,9 @@ def _write_int_tiff(path, data, *, nodata=None, scale=None, offset=None):
         coords={"y": np.arange(h, 0, -1) - 0.5, "x": np.arange(w) + 0.5},
         attrs=attrs,
     )
-    to_geotiff(da, path)
+    # A gdal_metadata SCALE/OFFSET dict on a fresh array is an
+    # experimental rich-tag write (#3320).
+    to_geotiff(da, path, allow_experimental_codecs="gdal_metadata" in attrs)
     return path
 
 
diff --git a/xrspatial/geotiff/tests/write/test_pack_band_subset_3161.py b/xrspatial/geotiff/tests/write/test_pack_band_subset_3161.py
index 0610982ec..45960fb75 100644
--- a/xrspatial/geotiff/tests/write/test_pack_band_subset_3161.py
+++ b/xrspatial/geotiff/tests/write/test_pack_band_subset_3161.py
@@ -33,7 +33,9 @@ def _write_two_band_tiff(path, *, gdal_metadata, nodata=65535):
         coords={"y": [1.5, 0.5], "x": [0.5, 1.5, 2.5]},
         attrs={"crs": 4326, "nodata": nodata, "gdal_metadata": gdal_metadata},
     )
-    to_geotiff(da, path)
+    # gdal_metadata dict on a fresh array is an experimental rich-tag
+    # write (#3320).
+    to_geotiff(da, path, allow_experimental_codecs=True)
     return path, data
 
 
diff --git a/xrspatial/geotiff/tests/write/test_pack_float_width_3080.py b/xrspatial/geotiff/tests/write/test_pack_float_width_3080.py
index e4e1fb862..cca9a9163 100644
--- a/xrspatial/geotiff/tests/write/test_pack_float_width_3080.py
+++ b/xrspatial/geotiff/tests/write/test_pack_float_width_3080.py
@@ -39,7 +39,9 @@ def _write_f32_tiff(path, data, *, nodata=None, scale=None, offset=None):
         coords={"y": np.arange(h, 0, -1) - 0.5, "x": np.arange(w) + 0.5},
         attrs=attrs,
     )
-    to_geotiff(da, path)
+    # A gdal_metadata SCALE/OFFSET dict on a fresh array is an
+    # experimental rich-tag write (#3320).
+    to_geotiff(da, path, allow_experimental_codecs="gdal_metadata" in attrs)
     return path
 
 
diff --git a/xrspatial/geotiff/tests/write/test_pack_lazy_nan_guard_3235.py b/xrspatial/geotiff/tests/write/test_pack_lazy_nan_guard_3235.py
index c94d681b1..5e04e5de9 100644
--- a/xrspatial/geotiff/tests/write/test_pack_lazy_nan_guard_3235.py
+++ b/xrspatial/geotiff/tests/write/test_pack_lazy_nan_guard_3235.py
@@ -28,7 +28,9 @@ def _write_packed_no_sentinel_tiff(path, data, *, scale="0.1", offset="5.0"):
         attrs={"crs": 4326,
                "gdal_metadata": {"SCALE": scale, "OFFSET": offset}},
     )
-    to_geotiff(da, str(path))
+    # gdal_metadata dict on a fresh array is an experimental rich-tag
+    # write (#3320).
+    to_geotiff(da, str(path), allow_experimental_codecs=True)
     return str(path)
 
 
diff --git a/xrspatial/geotiff/tests/write/test_pack_nodata_kwarg_3168.py b/xrspatial/geotiff/tests/write/test_pack_nodata_kwarg_3168.py
index 94f2f0f2a..17d71c56f 100644
--- a/xrspatial/geotiff/tests/write/test_pack_nodata_kwarg_3168.py
+++ b/xrspatial/geotiff/tests/write/test_pack_nodata_kwarg_3168.py
@@ -36,7 +36,9 @@ def _write_int_tiff(path, data, *, nodata=None, scale=None, offset=None):
         coords={"y": np.arange(h, 0, -1) - 0.5, "x": np.arange(w) + 0.5},
         attrs=attrs,
     )
-    to_geotiff(da, path)
+    # A gdal_metadata SCALE/OFFSET dict on a fresh array is an
+    # experimental rich-tag write (#3320).
+    to_geotiff(da, path, allow_experimental_codecs="gdal_metadata" in attrs)
     return path
 
 
diff --git a/xrspatial/geotiff/tests/write/test_pack_range_guard_3260.py b/xrspatial/geotiff/tests/write/test_pack_range_guard_3260.py
index 7b65e4c69..f181f8329 100644
--- a/xrspatial/geotiff/tests/write/test_pack_range_guard_3260.py
+++ b/xrspatial/geotiff/tests/write/test_pack_range_guard_3260.py
@@ -33,7 +33,8 @@ def _write_scaled_int16(path, *, nodata=None):
         coords={"y": [1.5, 0.5], "x": [0.5, 1.5]},
         attrs=attrs,
     )
-    to_geotiff(da, str(path), nodata=nodata)
+    to_geotiff(da, str(path), nodata=nodata,
+               allow_experimental_codecs=True)
     return str(path)
 
 
@@ -79,7 +80,7 @@ def test_pack_rejects_underflow_unsigned(tmp_path, chunks):
                "gdal_metadata": {"SCALE": "0.5", "OFFSET": "0.0"}},
     )
     src = str(tmp_path / "src_u16_underflow_3260.tif")
-    to_geotiff(da, src)
+    to_geotiff(da, src, allow_experimental_codecs=True)
 
     mod = _unpacked(src)
     mod.data[0, 0] = -1.0  # packs to -2, below uint16 min
@@ -127,7 +128,7 @@ def test_pack_accepts_full_dtype_range(tmp_path, chunks):
                "gdal_metadata": {"SCALE": "0.1", "OFFSET": "0.0"}},
     )
     src = str(tmp_path / "src_bounds_3260.tif")
-    to_geotiff(da, src)
+    to_geotiff(da, src, allow_experimental_codecs=True)
 
     mod = _unpacked(src)
     if chunks is not None:
@@ -163,7 +164,8 @@ def test_pack_float_target_not_range_guarded(tmp_path):
                "gdal_metadata": {"SCALE": "2.0", "OFFSET": "0.0"}},
     )
     src = str(tmp_path / "src_float_3260.tif")
-    to_geotiff(da, src, nodata=-9999.0)
+    to_geotiff(da, src, nodata=-9999.0,
+               allow_experimental_codecs=True)
 
     mod = _unpacked(src)
     mod.data[0, 0] = 1e30