diff --git a/mmv1/products/tags/TagKey.yaml b/mmv1/products/tags/TagKey.yaml
index ff5f57139453..a40e746f9130 100644
--- a/mmv1/products/tags/TagKey.yaml
+++ b/mmv1/products/tags/TagKey.yaml
@@ -47,6 +47,7 @@ iam_policy:
   parent_resource_attribute: 'tag_key'
   iam_conditions_request_type: 'REQUEST_BODY'
 custom_code:
+  constants: 'templates/terraform/constants/tags.go.tmpl'
 exclude_tgc: true
 examples:
   - name: 'tag_key_basic'
@@ -125,7 +126,7 @@ properties:
 
       Purpose data corresponds to the policy system that the tag is intended for. For example, the GCE_FIREWALL purpose expects data in the following format: `network = "<project-name>/<vpc-name>"`.
     immutable: true
-    ignore_read: true
+    diff_suppress_func: 'TagKeyPurposeDataDiffSuppress'
   - name: 'allowedValuesRegex'
     type: String
     description: |
diff --git a/mmv1/templates/terraform/constants/tags.go.tmpl b/mmv1/templates/terraform/constants/tags.go.tmpl
new file mode 100644
index 000000000000..9f9595fcb59f
--- /dev/null
+++ b/mmv1/templates/terraform/constants/tags.go.tmpl
@@ -0,0 +1,13 @@
+// TagKeyPurposeDataDiffSuppress suppresses diffs for purpose_data when the API
+// returns normalized values. For example, the API may resolve "auto" to an
+// actual organization number. Since purpose_data is immutable, if the old value
+// (from state) exists and is non-empty, we suppress the diff to avoid
+// unnecessary replacements after import.
+func TagKeyPurposeDataDiffSuppress(k, old, new string, d *schema.ResourceData) bool {
+	// If the old value exists and the field is set in state, suppress the diff
+	// since the API normalizes values (e.g., "auto" -> actual org number)
+	if old != "" && new != "" {
+		return true
+	}
+	return false
+}