The Google Assistant situation is a huge mess at the moment. There are three different Google Assistants, and each have a specific featureset, which means some things are missing from one of them but not others, and so on. The Google Assistant that's exclusively built into the OS of the Pixel and Pixel XL phones can only take commands via voice - you simply can't write in order to ask it something. On the other hand, the Google Assistant that lives inside the Allo chat app can be talked to or texted, but only replies via text and never speaks to you. The third Google Assistant is the one you can find in the Google Home device, which has its own frustrating set of limitations, such as no support for multiple accounts.
Will this change in the future? Probably, but it remains to be seen how fast Google can move - and if it even wants the Google Assistant brand to mean a consistent featureset regardless of which particular implementation you happen to be using. The company has already announced that the Assistant is headed to Android Wear smartwatches, as well as Android TVs. Nothing about more phones getting it, though - perhaps it's still too important of a selling point for the Pixels.
Through a teardown of the APK file for a new beta release of the Google app for Android, the folks over at Android Police have discovered that support for keyboard-based input is at least coming to the Google Assistant for the Pixel and Pixel XL. When this goes live, a keyboard icon will show up while you interact with the Assistant, and tapping it will let you type your query. It will be interesting to see if the Assistant will then adapt how it responds based on how you asked - so speaking to you if you speak to it but only showing you a written response if you used the keyboard.
Google has also started working on the Android Wear integration for the Assistant, which is also evident from the aforementioned teardown. What's still a big mystery is whether you'll be able to use it if you have an Android Wear smartwatch regardless of what phone it's paired to, or only if you also have a Pixel.
Finally, there's an intriguing mention of "search gestures" in the APK, which may mean you'll be able to perform some sort of gesture in order to get to the search interface in the Google Now Launcher or the Pixel Launcher.
Said no one ever.
Not true. I've been able to type into my Assistant on my Pixel XL since the day I got it. (And I pre-ordered it the day they were available.) It uses voice or text. It replies by whichever method you used to input (voice/text). It isn't "getting" a k...
Nice joke. google assistant is way better compare to cortana.