diff --git a/CHANGELOG.md b/CHANGELOG.md
index 850c525..e8df3c1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,23 @@ This format follows [Keep a Changelog](https://keepachangelog.com/) and adheres
 ## [Unreleased]
 
 ### Fixed
+- **Prompt-agent deploy: `stage` no longer fails with `Required properties ["kind"] are not present` against `azure-ai-projects` 2.x.**
+  `_copy_definition` previously called `.copy()` on the typed
+  `PromptAgentDefinition` returned by `get_version`. In SDK 1.x that
+  preserved the typed model so the body serialized as a flat
+  `{"kind": "prompt", "model": ..., "instructions": ...}`. In SDK 2.x
+  the same `.copy()` returns a stripped base `Model` whose JSON shape
+  is `{"_data": {"kind": "prompt", ...}}`, and `.get("kind")` returns
+  `None` — so the request body that reached the Foundry Agents service
+  contained `definition: {"_data": {...}}` with no top-level `kind`,
+  and the service rejected it with `invalid_payload`. This regression
+  only fired on the `created` action path (i.e. when the user's prompt
+  differed from the seed); the `reused` and bootstrap paths were
+  unaffected because they don't round-trip the typed model through
+  `.copy()`. `_copy_definition` now normalizes any SDK definition
+  object to a plain `dict` before mutation, and `_create_agent_version`
+  no longer puts a root-level `kind` on the request body (the new API
+  treats `kind` strictly as the discriminator inside `definition`).
 - **Tutorial: prompt-agent step 13 now shows the steady-state `foundry-agent.json` (action: reused) instead of the bootstrap edge case.**
   The example JSON in step 13 previously showed `action: bootstrapped`
   with `candidate_agent: "travel-agent:1"` and a "the two numbers are
diff --git a/src/agentops/pipeline/prompt_deploy.py b/src/agentops/pipeline/prompt_deploy.py
index b8464a0..331c21c 100644
--- a/src/agentops/pipeline/prompt_deploy.py
+++ b/src/agentops/pipeline/prompt_deploy.py
@@ -318,11 +318,9 @@ def _create_agent_version(
     description: str,
 ) -> Any:
     client = _project_client(endpoint)
-    # The current Foundry Agents create_version endpoint validates both a root
-    # `kind` discriminator and the nested `definition` payload.
-    body = {
-        "kind": _get_definition_value(definition, "kind"),
-        "definition": definition,
+    definition_dict = _definition_to_dict(definition)
+    body: Dict[str, Any] = {
+        "definition": definition_dict,
         "metadata": metadata,
         "description": description,
     }
@@ -380,13 +378,41 @@ def _get_mapping_value(value: Any, key: str) -> Any:
     return None
 
 
-def _copy_definition(definition: Any) -> Any:
-    if hasattr(definition, "copy"):
+def _copy_definition(definition: Any) -> Dict[str, Any]:
+    """Return a deep copy of ``definition`` as a plain dict.
+
+    The Foundry SDK's typed definition models (e.g. ``PromptAgentDefinition``)
+    expose ``.copy()``, but in ``azure-ai-projects`` 2.x that returns a stripped
+    base ``Model`` whose JSON shape is ``{"_data": {...}}`` instead of the
+    flattened payload the service expects. To stay compatible across SDK
+    versions we always normalize to a plain dict here.
+    """
+
+    return copy.deepcopy(_definition_to_dict(definition))
+
+
+def _definition_to_dict(definition: Any) -> Dict[str, Any]:
+    """Best-effort conversion of an SDK definition object into a plain dict."""
+
+    if isinstance(definition, dict):
+        return dict(definition)
+    data = getattr(definition, "_data", None)
+    if isinstance(data, dict):
+        return dict(data)
+    if hasattr(definition, "items"):
         try:
-            return definition.copy()
-        except TypeError:
+            return {key: value for key, value in definition.items()}
+        except Exception:  # noqa: BLE001 — fall through to attribute scrape
             pass
-    return copy.deepcopy(definition)
+    if hasattr(definition, "as_dict"):
+        try:
+            return dict(definition.as_dict())
+        except Exception:  # noqa: BLE001
+            pass
+    raise TypeError(
+        f"Cannot convert Foundry agent definition of type {type(definition).__name__} "
+        "to a dict; expected a mapping-compatible object."
+    )
 
 
 def _deployment_metadata(*, environment: str, prompt_hash: str) -> Dict[str, str]:
diff --git a/tests/unit/test_prompt_deploy.py b/tests/unit/test_prompt_deploy.py
index 2816cb7..92f0256 100644
--- a/tests/unit/test_prompt_deploy.py
+++ b/tests/unit/test_prompt_deploy.py
@@ -374,3 +374,83 @@ def test_is_not_found_error_handles_404_and_rejects_others() -> None:
     assert not prompt_deploy._is_not_found_error(_make_not_found(403))
     assert not prompt_deploy._is_not_found_error(_make_not_found(500))
     assert not prompt_deploy._is_not_found_error(Exception("no status"))
+
+
+def test_copy_definition_returns_plain_dict_from_sdk_typed_model() -> None:
+    """Regression: ``azure-ai-projects`` 2.x typed definition models expose a
+    ``.copy()`` method that returns a stripped base ``Model`` whose JSON shape
+    is ``{"_data": {...}}`` instead of the flat fields the Foundry service
+    expects. ``_copy_definition`` must normalize to a plain dict so the
+    ``definition`` payload reaches the wire as a flat object with ``kind`` at
+    the top level.
+    """
+
+    class _FakeTypedModel:
+        """Mimics the surface of ``PromptAgentDefinition`` from SDK 2.x."""
+
+        def __init__(self, data: dict) -> None:
+            self._data = dict(data)
+
+        def get(self, key, default=None):
+            return self._data.get(key, default)
+
+        def items(self):
+            return self._data.items()
+
+        def copy(self):
+            stripped = _FakeTypedModel.__new__(_FakeTypedModel)
+            stripped._data = dict(self._data)
+            return stripped
+
+    typed = _FakeTypedModel(
+        {"kind": "prompt", "model": "gpt-4o-mini", "instructions": "hi"}
+    )
+
+    copied = prompt_deploy._copy_definition(typed)
+
+    assert isinstance(copied, dict)
+    assert copied == {
+        "kind": "prompt",
+        "model": "gpt-4o-mini",
+        "instructions": "hi",
+    }
+    assert "_data" not in copied
+
+
+def test_create_agent_version_body_uses_flat_definition_dict(monkeypatch) -> None:
+    """The body sent to ``client.agents.create_version`` must contain a flat
+    ``definition`` dict (not the SDK's ``{"_data": {...}}`` shape) and must
+    not include a body-root ``kind`` — the new Foundry API treats ``kind`` as
+    the polymorphic discriminator inside ``definition``.
+    """
+
+    captured: dict = {}
+
+    class _FakeAgents:
+        def create_version(self, agent_name, *, body):
+            captured["agent_name"] = agent_name
+            captured["body"] = body
+            return SimpleNamespace(id="agent-version-9", version="9")
+
+    class _FakeClient:
+        agents = _FakeAgents()
+
+    monkeypatch.setattr(prompt_deploy, "_project_client", lambda endpoint: _FakeClient())
+
+    definition = {"kind": "prompt", "model": "gpt-4o-mini", "instructions": "hi"}
+
+    result = prompt_deploy._create_agent_version(
+        "https://example/api/projects/p",
+        "travel-agent",
+        definition,
+        metadata={"agentops.env": "dev"},
+        description="desc",
+    )
+
+    assert result.version == "9"
+    body = captured["body"]
+    assert "kind" not in body, "body-root 'kind' is no longer valid in SDK 2.x"
+    assert body["definition"] == definition
+    assert body["definition"]["kind"] == "prompt"
+    assert body["metadata"] == {"agentops.env": "dev"}
+    assert body["description"] == "desc"