diff --git a/.fern/metadata.json b/.fern/metadata.json
index a3ccea9..214386a 100644
--- a/.fern/metadata.json
+++ b/.fern/metadata.json
@@ -5,6 +5,6 @@
   "generatorConfig": {
     "client_class_name": "PhenomlClient"
   },
-  "originGitCommit": "cdfe611a02d68f09dbce1eb259387269402552fb",
-  "sdkVersion": "9.0.0"
+  "originGitCommit": "670d2f19d924d953196b4131bb16a252f2b6148f",
+  "sdkVersion": "9.1.0"
 }
\ No newline at end of file
diff --git a/changelog.md b/changelog.md
index 4ec42e9..2510822 100644
--- a/changelog.md
+++ b/changelog.md
@@ -1,3 +1,6 @@
+## 9.1.0 - 2026-03-11
+* The workflow execution methods now support an optional `preview` parameter. When set to true, workflows return mock resources instead of persisting data to the FHIR server, enabling safe testing and development.
+
 ## 9.0.0 - 2026-03-11
 * The `ErrorResponse` type has been removed from the summary module. If your code references `phenoml.summary.ErrorResponse` or imports it directly, you'll need to update your error handling logic to use the appropriate error types for your specific use case.
 
diff --git a/pyproject.toml b/pyproject.toml
index a04a9d1..2165cd0 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ dynamic = ["version"]
 
 [tool.poetry]
 name = "phenoml"
-version = "9.0.0"
+version = "9.1.0"
 description = ""
 readme = "README.md"
 authors = []
diff --git a/reference.md b/reference.md
index f714f31..f935b42 100644
--- a/reference.md
+++ b/reference.md
@@ -6689,6 +6689,14 @@ client.workflows.execute(
 <dl>
 <dd>
 
+**preview:** `typing.Optional[bool]` — If true, create operations return mock resources instead of persisting to the FHIR server
+    
+</dd>
+</dl>
+
+<dl>
+<dd>
+
 **request_options:** `typing.Optional[RequestOptions]` — Request-specific configuration.
     
 </dd>
diff --git a/src/phenoml/core/client_wrapper.py b/src/phenoml/core/client_wrapper.py
index f21da3c..e13d82d 100644
--- a/src/phenoml/core/client_wrapper.py
+++ b/src/phenoml/core/client_wrapper.py
@@ -27,12 +27,12 @@ def get_headers(self) -> typing.Dict[str, str]:
         import platform
 
         headers: typing.Dict[str, str] = {
-            "User-Agent": "phenoml/9.0.0",
+            "User-Agent": "phenoml/9.1.0",
             "X-Fern-Language": "Python",
             "X-Fern-Runtime": f"python/{platform.python_version()}",
             "X-Fern-Platform": f"{platform.system().lower()}/{platform.release()}",
             "X-Fern-SDK-Name": "phenoml",
-            "X-Fern-SDK-Version": "9.0.0",
+            "X-Fern-SDK-Version": "9.1.0",
             **(self.get_custom_headers() or {}),
         }
         token = self._get_token()
diff --git a/src/phenoml/workflows/client.py b/src/phenoml/workflows/client.py
index b08af65..790051a 100644
--- a/src/phenoml/workflows/client.py
+++ b/src/phenoml/workflows/client.py
@@ -279,6 +279,7 @@ def execute(
         id: str,
         *,
         input_data: typing.Dict[str, typing.Any],
+        preview: typing.Optional[bool] = OMIT,
         request_options: typing.Optional[RequestOptions] = None,
     ) -> ExecuteWorkflowResponse:
         """
@@ -292,6 +293,9 @@ def execute(
         input_data : typing.Dict[str, typing.Any]
             Input data for workflow execution
 
+        preview : typing.Optional[bool]
+            If true, create operations return mock resources instead of persisting to the FHIR server
+
         request_options : typing.Optional[RequestOptions]
             Request-specific configuration.
 
@@ -315,7 +319,9 @@ def execute(
             },
         )
         """
-        _response = self._raw_client.execute(id, input_data=input_data, request_options=request_options)
+        _response = self._raw_client.execute(
+            id, input_data=input_data, preview=preview, request_options=request_options
+        )
         return _response.data
 
 
@@ -622,6 +628,7 @@ async def execute(
         id: str,
         *,
         input_data: typing.Dict[str, typing.Any],
+        preview: typing.Optional[bool] = OMIT,
         request_options: typing.Optional[RequestOptions] = None,
     ) -> ExecuteWorkflowResponse:
         """
@@ -635,6 +642,9 @@ async def execute(
         input_data : typing.Dict[str, typing.Any]
             Input data for workflow execution
 
+        preview : typing.Optional[bool]
+            If true, create operations return mock resources instead of persisting to the FHIR server
+
         request_options : typing.Optional[RequestOptions]
             Request-specific configuration.
 
@@ -666,5 +676,7 @@ async def main() -> None:
 
         asyncio.run(main())
         """
-        _response = await self._raw_client.execute(id, input_data=input_data, request_options=request_options)
+        _response = await self._raw_client.execute(
+            id, input_data=input_data, preview=preview, request_options=request_options
+        )
         return _response.data
diff --git a/src/phenoml/workflows/raw_client.py b/src/phenoml/workflows/raw_client.py
index 2c4e08a..b14f8d8 100644
--- a/src/phenoml/workflows/raw_client.py
+++ b/src/phenoml/workflows/raw_client.py
@@ -543,6 +543,7 @@ def execute(
         id: str,
         *,
         input_data: typing.Dict[str, typing.Any],
+        preview: typing.Optional[bool] = OMIT,
         request_options: typing.Optional[RequestOptions] = None,
     ) -> HttpResponse[ExecuteWorkflowResponse]:
         """
@@ -556,6 +557,9 @@ def execute(
         input_data : typing.Dict[str, typing.Any]
             Input data for workflow execution
 
+        preview : typing.Optional[bool]
+            If true, create operations return mock resources instead of persisting to the FHIR server
+
         request_options : typing.Optional[RequestOptions]
             Request-specific configuration.
 
@@ -569,6 +573,7 @@ def execute(
             method="POST",
             json={
                 "input_data": input_data,
+                "preview": preview,
             },
             headers={
                 "content-type": "application/json",
@@ -1162,6 +1167,7 @@ async def execute(
         id: str,
         *,
         input_data: typing.Dict[str, typing.Any],
+        preview: typing.Optional[bool] = OMIT,
         request_options: typing.Optional[RequestOptions] = None,
     ) -> AsyncHttpResponse[ExecuteWorkflowResponse]:
         """
@@ -1175,6 +1181,9 @@ async def execute(
         input_data : typing.Dict[str, typing.Any]
             Input data for workflow execution
 
+        preview : typing.Optional[bool]
+            If true, create operations return mock resources instead of persisting to the FHIR server
+
         request_options : typing.Optional[RequestOptions]
             Request-specific configuration.
 
@@ -1188,6 +1197,7 @@ async def execute(
             method="POST",
             json={
                 "input_data": input_data,
+                "preview": preview,
             },
             headers={
                 "content-type": "application/json",
diff --git a/src/phenoml/workflows/types/execute_workflow_response.py b/src/phenoml/workflows/types/execute_workflow_response.py
index 61e4e8a..acd41bd 100644
--- a/src/phenoml/workflows/types/execute_workflow_response.py
+++ b/src/phenoml/workflows/types/execute_workflow_response.py
@@ -19,6 +19,10 @@ class ExecuteWorkflowResponse(UniversalBaseModel):
     """
 
     results: typing.Optional[ExecuteWorkflowResponseResults] = None
+    preview: typing.Optional[bool] = pydantic.Field(default=None)
+    """
+    Whether the workflow was executed in preview mode
+    """
 
     if IS_PYDANTIC_V2:
         model_config: typing.ClassVar[pydantic.ConfigDict] = pydantic.ConfigDict(extra="allow", frozen=True)  # type: ignore # Pydantic v2