@java.lang.Override
  public Builder toBuilder() {
    return this == DEFAULT_INSTANCE ? new Builder() : new Builder().mergeFrom(this);
  }
<pre>
API version used to start the operation.
</pre>

<code>string api_version = 5;</code>

@return The bytes for apiVersion.
java-workflows/proto-google-cloud-workflows-v1beta/src/main/java/com/google/cloud/workflows/v1beta/OperationMetadata.java