zarr-developers · d-v-b · Jun 25, 2026 · May 31, 2026 · Jun 6, 2026 · Jun 6, 2026
diff --git a/changes/202.bugfix.md b/changes/202.bugfix.md
@@ -0,0 +1 @@
+Stop emitting an `UnstableSpecificationWarning` when serializing the `struct` data type to Zarr V3 metadata. The `struct` data type now has a stable Zarr V3 specification. The legacy `structured` alias and the unspecified `null_terminated_bytes`, `raw_bytes`, and `variable_length_bytes` data types continue to warn.
diff --git a/src/zarr/core/dtype/npy/structured.py b/src/zarr/core/dtype/npy/structured.py
@@ -589,7 +589,9 @@ def to_json(self, zarr_format: ZarrFormat) -> StructuredJSON_V2 | StructJSON_V3:
             ]
             return {"name": fields_v2, "object_codec_id": None}
         elif zarr_format == 3:
-            v3_unstable_dtype_warning(self)
+            # The "struct" data type has a stable Zarr V3 specification
+            # (https://github.com/zarr-developers/zarr-extensions/tree/main/data-types/struct),
+            # so unlike the legacy "structured" alias it does not emit an unstable-spec warning.
             fields_v3 = [
                 {"name": f_name, "data_type": f_dtype.to_json(zarr_format=zarr_format)}
                 for f_name, f_dtype in self.fields
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Stop emitting an `UnstableSpecificationWarning` when serializing the `struct` data type to Zarr V3 metadata. The `struct` data type now has a stable Zarr V3 specification. The legacy `structured` alias and the unspecified `null_terminated_bytes`, `raw_bytes`, and `variable_length_bytes` data types continue to warn.