diff --git a/google/cloud/aiplatform/v1beta1/genai_tuning_service.proto b/google/cloud/aiplatform/v1beta1/genai_tuning_service.proto
index cc44a829f9..124db6e52e 100644
--- a/google/cloud/aiplatform/v1beta1/genai_tuning_service.proto
+++ b/google/cloud/aiplatform/v1beta1/genai_tuning_service.proto
@@ -20,7 +20,10 @@ import "google/api/annotations.proto";
 import "google/api/client.proto";
 import "google/api/field_behavior.proto";
 import "google/api/resource.proto";
+import "google/cloud/aiplatform/v1beta1/io.proto";
+import "google/cloud/aiplatform/v1beta1/operation.proto";
 import "google/cloud/aiplatform/v1beta1/tuning_job.proto";
+import "google/longrunning/operations.proto";
 import "google/protobuf/empty.proto";
 
 option csharp_namespace = "Google.Cloud.AIPlatform.V1Beta1";
@@ -82,6 +85,22 @@ service GenAiTuningService {
     };
     option (google.api.method_signature) = "name";
   }
+
+  // Rebase a TunedModel.
+  // Creates a LongRunningOperation that takes a legacy Tuned GenAI model
+  // Reference and creates a TuningJob based on newly available model.
+  rpc RebaseTunedModel(RebaseTunedModelRequest)
+      returns (google.longrunning.Operation) {
+    option (google.api.http) = {
+      post: "/v1beta1/{parent=projects/*/locations/*}/tuningJobs:rebaseTunedModel"
+      body: "*"
+    };
+    option (google.api.method_signature) = "parent,tuned_model_ref";
+    option (google.longrunning.operation_info) = {
+      response_type: "TuningJob"
+      metadata_type: "RebaseTunedModelOperationMetadata"
+    };
+  }
 }
 
 // Request message for
@@ -162,3 +181,39 @@ message CancelTuningJobRequest {
     }
   ];
 }
+
+// Request message for
+// [GenAiTuningService.RebaseTunedModel][google.cloud.aiplatform.v1beta1.GenAiTuningService.RebaseTunedModel].
+message RebaseTunedModelRequest {
+  // Required. The resource name of the Location into which to rebase the Model.
+  // Format: `projects/{project}/locations/{location}`
+  string parent = 1 [
+    (google.api.field_behavior) = REQUIRED,
+    (google.api.resource_reference) = {
+      type: "locations.googleapis.com/Location"
+    }
+  ];
+
+  // Required. TunedModel reference to retrieve the legacy model information.
+  TunedModelRef tuned_model_ref = 2 [(google.api.field_behavior) = REQUIRED];
+
+  // Optional. The TuningJob to be updated. Users can use this TuningJob field
+  // to overwrite tuning configs.
+  TuningJob tuning_job = 3 [(google.api.field_behavior) = OPTIONAL];
+
+  // Optional. The Google Cloud Storage location to write the artifacts.
+  GcsDestination artifact_destination = 4
+      [(google.api.field_behavior) = OPTIONAL];
+
+  // Optional. By default, bison to gemini migration will always create new
+  // model/endpoint, but for gemini-1.0 to gemini-1.5 migration, we default
+  // deploy to the same endpoint. See details in this Section.
+  bool deploy_to_same_endpoint = 5 [(google.api.field_behavior) = OPTIONAL];
+}
+
+// Runtime operation information for
+// [GenAiTuningService.RebaseTunedModel][google.cloud.aiplatform.v1beta1.GenAiTuningService.RebaseTunedModel].
+message RebaseTunedModelOperationMetadata {
+  // The common part of the operation generic information.
+  GenericOperationMetadata generic_metadata = 1;
+}
diff --git a/google/cloud/aiplatform/v1beta1/tuning_job.proto b/google/cloud/aiplatform/v1beta1/tuning_job.proto
index 308b2bc964..0693914641 100644
--- a/google/cloud/aiplatform/v1beta1/tuning_job.proto
+++ b/google/cloud/aiplatform/v1beta1/tuning_job.proto
@@ -384,7 +384,7 @@ message SupervisedHyperParameters {
   AdapterSize adapter_size = 3 [(google.api.field_behavior) = OPTIONAL];
 }
 
-// Tuning Spec for Supervised Tuning.
+// Tuning Spec for Supervised Tuning for first party models.
 message SupervisedTuningSpec {
   // Required. Cloud Storage path to file containing training dataset for
   // tuning. The dataset must be formatted as a JSONL file.
@@ -450,3 +450,26 @@ message DistillationHyperParameters {
   SupervisedHyperParameters.AdapterSize adapter_size = 3
       [(google.api.field_behavior) = OPTIONAL];
 }
+
+// TunedModel Reference for legacy model migration.
+message TunedModelRef {
+  // The Tuned Model Reference for the model.
+  oneof tuned_model_ref {
+    // Support migration from model registry.
+    string tuned_model = 1 [(google.api.resource_reference) = {
+      type: "aiplatform.googleapis.com/Model"
+    }];
+
+    // Support migration from tuning job list page, from gemini-1.0-pro-002
+    // to 1.5 and above.
+    string tuning_job = 2 [(google.api.resource_reference) = {
+      type: "aiplatform.googleapis.com/TuningJob"
+    }];
+
+    // Support migration from tuning job list page, from bison model to gemini
+    // model.
+    string pipeline_job = 3 [(google.api.resource_reference) = {
+      type: "aiplatform.googleapis.com/PipelineJob"
+    }];
+  }
+}