diff --git a/docs/PromptVersion.md b/docs/PromptVersion.md
index 7305a9b..f8d8192 100644
--- a/docs/PromptVersion.md
+++ b/docs/PromptVersion.md
@@ -11,7 +11,7 @@ Name | Type | Description | Notes
 **template** | **str** | The template syntax code with Go template parameters. | 
 **status** | **str** | Active lifecycle status of this template version. | 
 **created_at** | **datetime** |  | 
-**published_at** | **datetime** | Timestamp when status was set to live. Null if draft. | 
+**published_at** | **datetime** | Timestamp when status was set to live. Null if draft. | [optional] 
 **tags** | **List[str]** | List of tag strings attached to this version. | 
 
 ## Example
diff --git a/px0/models/prompt_version.py b/px0/models/prompt_version.py
index 8754646..e9de865 100644
--- a/px0/models/prompt_version.py
+++ b/px0/models/prompt_version.py
@@ -34,7 +34,7 @@ class PromptVersion(BaseModel):
     template: StrictStr = Field(description="The template syntax code with Go template parameters.")
     status: StrictStr = Field(description="Active lifecycle status of this template version.")
     created_at: datetime
-    published_at: datetime = Field(description="Timestamp when status was set to live. Null if draft.")
+    published_at: Optional[datetime] = Field(default=None, description="Timestamp when status was set to live. Null if draft.")
     tags: List[StrictStr] = Field(description="List of tag strings attached to this version.")
     __properties: ClassVar[List[str]] = ["id", "prompt_id", "version", "template", "status", "created_at", "published_at", "tags"]
 
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_prompt_version_published_at.py b/tests/test_prompt_version_published_at.py
new file mode 100644
index 0000000..7a49601
--- /dev/null
+++ b/tests/test_prompt_version_published_at.py
@@ -0,0 +1,57 @@
+"""Regression tests for PromptVersion.published_at nullability.
+
+A version only has a ``published_at`` timestamp once it has been set to
+``live``. For ``draft``, ``stable`` and ``archived`` versions the server
+returns ``published_at: null``, so the field must be optional; otherwise
+deserializing any non-live version raises pydantic ``ValidationError``.
+"""
+import datetime
+
+from px0.models.prompt_version import PromptVersion
+from px0.models.list_versions200_response import ListVersions200Response
+
+
+def _draft_payload():
+    return {
+        "id": "ver_1",
+        "prompt_id": "prm_1",
+        "version": 1,
+        "template": "Hello {{.name}}!",
+        "status": "draft",
+        "created_at": "2024-01-01T00:00:00Z",
+        "published_at": None,
+        "tags": [],
+    }
+
+
+def test_draft_version_with_null_published_at_deserializes():
+    version = PromptVersion.from_dict(_draft_payload())
+    assert version is not None
+    assert version.published_at is None
+    assert version.status == "draft"
+
+
+def test_published_at_omitted_entirely_deserializes():
+    payload = _draft_payload()
+    del payload["published_at"]
+    version = PromptVersion.from_dict(payload)
+    assert version.published_at is None
+
+
+def test_live_version_keeps_published_at():
+    payload = _draft_payload()
+    payload["status"] = "live"
+    payload["published_at"] = "2024-01-02T03:04:05Z"
+    version = PromptVersion.from_dict(payload)
+    assert isinstance(version.published_at, datetime.datetime)
+
+
+def test_null_published_at_is_dropped_by_to_dict():
+    version = PromptVersion.from_dict(_draft_payload())
+    assert "published_at" not in version.to_dict()
+
+
+def test_list_versions_with_a_draft_element_deserializes():
+    response = ListVersions200Response.from_dict({"versions": [_draft_payload()]})
+    assert response is not None
+    assert response.versions[0].published_at is None