Well, as was notified by Google, the Google Lens started appearing to Assistant in both Pixel and Pixel 2 Phones. The visual search feature, which got debuted in Google Photos on the Pixel 2 earlier in October, however is a bit different when it comes to Assistant. While in the former, Lens was activated upon viewing an image, in Assistant, once you hold down the home button, Lens can be spotted on the sheet that pops up. The camera viewfinder opens up when you press the button in the bottom right corner.
That said, Google Lens in Assistant in the full mode would only be rolled out to Pixel owners, in the coming weeks.