diff --git a/vertexai/tuning/__init__.py b/vertexai/tuning/__init__.py
index 9b8362969b..2826753903 100644
--- a/vertexai/tuning/__init__.py
+++ b/vertexai/tuning/__init__.py
@@ -16,8 +16,10 @@
 
 # We just want to re-export certain classes
 # pylint: disable=g-multiple-import,g-importing-member
+from vertexai.tuning._tuning import SourceModel
 from vertexai.tuning._tuning import TuningJob
 
 __all__ = [
+    "SourceModel",
     "TuningJob",
 ]
diff --git a/vertexai/tuning/_supervised_tuning.py b/vertexai/tuning/_supervised_tuning.py
index a8b5b1ed17..7ab280b893 100644
--- a/vertexai/tuning/_supervised_tuning.py
+++ b/vertexai/tuning/_supervised_tuning.py
@@ -21,11 +21,15 @@
 )
 from vertexai import generative_models
 from vertexai.tuning import _tuning
+from vertexai.tuning import SourceModel
 
 
 def train(
     *,
-    source_model: Union[str, generative_models.GenerativeModel],
+    source_model: Union[
+            str,
+            generative_models.GenerativeModel,
+            SourceModel],
     train_dataset: str,
     validation_dataset: Optional[str] = None,
     tuned_model_display_name: Optional[str] = None,
@@ -33,6 +37,7 @@ def train(
     learning_rate_multiplier: Optional[float] = None,
     adapter_size: Optional[Literal[1, 4, 8, 16]] = None,
     labels: Optional[Dict[str, str]] = None,
+    output_uri: Optional[str] = None,
 ) -> "SupervisedTuningJob":
     """Tunes a model using supervised training.
 
@@ -49,7 +54,7 @@ def train(
         learning_rate_multiplier: Learning rate multiplier for tuning.
         adapter_size: Adapter size for tuning.
         labels: User-defined metadata to be associated with trained models
-
+        output_uri: The Google Cloud Storage location to write the model artifacts.
     Returns:
         A `TuningJob` object.
     """
@@ -94,6 +99,7 @@ def train(
             tuning_spec=supervised_tuning_spec,
             tuned_model_display_name=tuned_model_display_name,
             labels=labels,
+            output_uri=output_uri,
         )
     )
     _ipython_utils.display_model_tuning_button(supervised_tuning_job)
diff --git a/vertexai/tuning/_tuning.py b/vertexai/tuning/_tuning.py
index f080608dd9..1e0e34731d 100644
--- a/vertexai/tuning/_tuning.py
+++ b/vertexai/tuning/_tuning.py
@@ -42,6 +42,42 @@
 
 _LOGGER = aiplatform_base.Logger(__name__)
 
+class SourceModel:
+    r"""A model that is used in managed OSS supervised tuning.
+
+    Usage:
+        ```
+        model = SourceModel(
+            base_model="meta/llama3.1-8b",
+            custom_base_model="gs://user-bucket/custom-weights",
+        )
+        sft_tuning_job = sft.train(
+            source_model=model,
+            train_dataset="gs://my-bucket/train.jsonl",
+            validation_dataset="gs://my-bucket/validation.jsonl",
+            epochs=4,
+            learning_rate_multiplier=0.5,
+            tuned_model_display_name="my-tuned-model",
+            output_uri="gs://user-bucket/tuned-model"
+        )
+
+        while not sft_tuning_job.has_ended:
+            time.sleep(60)
+            sft_tuning_job.refresh()
+
+        tuned_model = aiplatform.Model(sft_tuning_job.tuned_model_name)
+        ```
+    """
+
+    def __init__(
+        self,
+        base_model: str,
+        custom_base_model: str = "",
+    ):
+        r"""Initializes SourceModel."""
+        self.base_model = base_model
+        self.custom_base_model = custom_base_model
+
 
 class TuningJobClientWithOverride(aiplatform_utils.ClientWithOverride):
     _is_temporary = True
@@ -132,7 +168,7 @@ def tuning_data_statistics(self) -> gca_tuning_job_types.TuningDataStats:
     def _create(
         cls,
         *,
-        base_model: str,
+        base_model: Union[str, SourceModel],
         tuning_spec: Union[
             gca_tuning_job_types.SupervisedTuningSpec,
             gca_tuning_job_types.DistillationSpec,
@@ -143,13 +179,13 @@ def _create(
         project: Optional[str] = None,
         location: Optional[str] = None,
         credentials: Optional[auth_credentials.Credentials] = None,
+        output_uri: Optional[str] = None,
     ) -> "TuningJob":
         r"""Submits TuningJob.
 
         Args:
-            base_model (str):
-                Model name for tuning, e.g., "gemini-1.0-pro"
-                or "gemini-1.0-pro-001".
+            base_model: Model for tuning:
+                Supported types: str, SourceModel.
 
                 This field is a member of `oneof`_ ``source_model``.
             tuning_spec: Tuning Spec for Fine Tuning.
@@ -178,6 +214,7 @@ def _create(
                 Overrides location set in aiplatform.init.
             credentials: Custom credentials to use to call tuning job service.
                 Overrides credentials set in aiplatform.init.
+            output_uri: The Google Cloud Storage location to write the artifacts.
 
         Returns:
             Submitted TuningJob.
@@ -191,17 +228,26 @@ def _create(
             tuned_model_display_name = cls._generate_display_name()
 
         gca_tuning_job = gca_tuning_job_types.TuningJob(
-            base_model=base_model,
             tuned_model_display_name=tuned_model_display_name,
             description=description,
             labels=labels,
-            # The tuning_spec one_of is set later
+            output_uri=output_uri,
         )
 
         if isinstance(tuning_spec, gca_tuning_job_types.SupervisedTuningSpec):
             gca_tuning_job.supervised_tuning_spec = tuning_spec
+            if isinstance(base_model, SourceModel):
+                gca_tuning_job.base_model = base_model.base_model
+                gca_tuning_job.custom_base_model = base_model.custom_base_model
+            else:
+                gca_tuning_job.base_model = base_model
         elif isinstance(tuning_spec, gca_tuning_job_types.DistillationSpec):
             gca_tuning_job.distillation_spec = tuning_spec
+            if isinstance(base_model, SourceModel):
+                raise RuntimeError(
+                    "Distillation is not supported for custom models."
+                )
+            gca_tuning_job.base_model = base_model
         else:
             raise RuntimeError(f"Unsupported tuning_spec kind: {tuning_spec}")