I have Bixby set as my default assistant. (fyi, this post is not an invitation to discuss the merits or demerits of either assistant) I grabbed my phone a bit awkwardly this morning and ended up long pressing the home key. Google Assistant launched. when I went to Default Apps, I saw that Google Assistant was the default. obviously, I never made that selection. therefore, after downloading the beta software, this change was made. hope this is helpful.