Q: Are you able to open pptx files in Keynote 6.5.3?

I am unable to import PowerPoint pptx files into Keynote 6.5.3. Only ppt files. But this claims there is pptx import support Keynote: Supported file formats - Apple Support and I could have sworn it worked for me not too long ago but I am certainly questioning that now. I've tried files saved by PowerPoint and Keynote files exported to pptx format. Is this working for anyone else?