diff --git a/internal/internal_nexus_task_handler.go b/internal/internal_nexus_task_handler.go
index 08589671a..2dc972d2c 100644
--- a/internal/internal_nexus_task_handler.go
+++ b/internal/internal_nexus_task_handler.go
@@ -246,17 +246,12 @@ func (h *nexusTaskHandler) handleStartOperation(
 			}
 		}
 		token := t.OperationToken
-		//lint:ignore SA1019 this field might be set by users of older SDKs.
-		if t.OperationID != "" {
-			token = t.OperationID //lint:ignore SA1019 this field might be set by users of older SDKs.
-		}
 		return &nexuspb.Response{
 			Variant: &nexuspb.Response_StartOperation{
 				StartOperation: &nexuspb.StartOperationResponse{
 					Variant: &nexuspb.StartOperationResponse_AsyncSuccess{
 						AsyncSuccess: &nexuspb.StartOperationResponse_Async{
 							OperationToken: token,
-							OperationId:    token,
 							Links:          links,
 						},
 					},
diff --git a/temporalnexus/operation.go b/temporalnexus/operation.go
index c4db1fc34..47b2856f9 100644
--- a/temporalnexus/operation.go
+++ b/temporalnexus/operation.go
@@ -187,7 +187,6 @@ func (o *workflowRunOperation[I, O]) Start(
 		nexus.AddHandlerLinks(ctx, handle.link())
 		return &nexus.HandlerStartOperationResultAsync{
 			OperationToken: handle.token(),
-			OperationID:    handle.token(),
 		}, nil
 	}
 
@@ -204,7 +203,6 @@ func (o *workflowRunOperation[I, O]) Start(
 	nexus.AddHandlerLinks(ctx, handle.link())
 	return &nexus.HandlerStartOperationResultAsync{
 		OperationToken: handle.token(),
-		OperationID:    handle.token(),
 	}, nil
 }
 
@@ -323,8 +321,8 @@ func ExecuteUntypedWorkflow[R any](
 			nexusOptions.CallbackHeader = make(nexus.Header)
 		}
 
-		//lint:ignore SA1019 this field is expected to be populated by servers older than 1.27.0.
-		nexusOptions.CallbackHeader.Set(nexus.HeaderOperationID, encodedToken)
+		// This field is expected to be populated by servers older than 1.27.0.
+		nexusOptions.CallbackHeader.Set("nexus-operation-id", encodedToken)
 		nexusOptions.CallbackHeader.Set(nexus.HeaderOperationToken, encodedToken)
 		internal.SetCallbacksOnStartWorkflowOptions(&startWorkflowOptions, []*common.Callback{
 			{