diff --git a/neuralnetworks/1.0/IPreparedModel.hal b/neuralnetworks/1.0/IPreparedModel.hal
index 5df883e..ee406fb 100644
--- a/neuralnetworks/1.0/IPreparedModel.hal
+++ b/neuralnetworks/1.0/IPreparedModel.hal
@@ -16,7 +16,7 @@
 
 package android.hardware.neuralnetworks@1.0;
 
-import IEvent;
+import IExecutionCallback;
 
 /**
  * IPreparedModel describes a model that has been prepared for execution and
@@ -24,28 +24,42 @@
  */
 interface IPreparedModel {
     /**
-     * Spawns an asynchronous execution on a prepared model.
+     * Launches an asynchronous execution on a prepared model.
      *
-     * Executions are asynchronous with respect to the Neuralnetworks runtime.
-     * To support this, IPreparedModel::execute must spawn a new task and return
-     * whether the task was successfully launched. The asynchronous task which
-     * performs the execution must call event's IEvent::notify with the status
-     * of the execution immediately after the execution has finished.
+     * The execution is performed asynchronously with respect to the caller.
+     * execute must verify the inputs to the function are correct. If there is
+     * an error, execute must immediately invoke the callback with the
+     * appropriate ErrorStatus value, then return with the same ErrorStatus. If
+     * the inputs to the function are valid and there is no error, execute must
+     * launch an asynchronous task to perform the execution in the background,
+     * and immediately return with ErrorStatus::NONE. If the asynchronous task
+     * fails to launch, execute must immediately invoke the callback with
+     * ErrorStatus::GENERAL_FAILURE, then return with
+     * ErrorStatus::GENERAL_FAILURE.
      *
-     * Multiple threads can call this execute function concurrently.
+     * When the asynchronous task has finished its execution, it must
+     * immediately invoke the callback object provided as an input to the
+     * execute function. This callback must be provided with the ErrorStatus of
+     * the execution.
+     *
+     * Multiple threads can call the execute function on the same IPreparedModel
+     * object concurrently with different requests.
      *
      * @param request The input and output information on which the prepared
      *                model is to be executed.
-     * @param event A callback used for synchronization that must be signaled
-     *              once the execution has finished.
+     * @param callback A callback object used to return the error status of
+     *                 the execution. The callback object's notify function must
+     *                 be called exactly once, even if the execution was
+     *                 unsuccessful.
      * @return status Error status of the call, must be:
      *                - NONE if task is successfully launched
      *                - DEVICE_UNAVAILABLE if driver is offline or busy
      *                - GENERAL_FAILURE if there is an unspecified error
      *                - OUTPUT_INSUFFICIENT_SIZE if provided output buffer is
      *                  not large enough to store the resultant values
-     *                - INVALID_ARGUMENT when one of the input arguments is
+     *                - INVALID_ARGUMENT if one of the input arguments is
      *                  invalid
      */
-    execute(Request request, IEvent event) generates (ErrorStatus status);
+    execute(Request request, IExecutionCallback callback)
+        generates (ErrorStatus status);
 };