As per the android developers site, minimum sdk for Instant app is 21, ie 5.0. link
The site clearly states : Android Instant Apps are available on the majority of devices running Android 5.0 (API level 21) and higher.
But when we create a new project as per the guideline given in this link which states that we need to have minimum sdk of 23, to get instant app support.
And does not allow me to create a support for 5.0.
as shown in below image which I tried :
That requirement exists only in the setup wizard, and it is a bug. If you change the value to something lower after creating the project, you'll see that it builds fine and can run on API 21 and 22 devices.
The documentation is correct about supported Android versions, but note that even that doesn't dictate any particular minSdkVersion. You can build an instant app with a minSdkVersion lower than 21. It just won't run on anything before 21, since the Instant Apps Runtime itself is restricted to 21+.
For that reason, this check was always a bug, even when we didn't support devices before 23. I was told it was fixed in 3.0, though I didn't verify. I checked tonight and confirmed that the check is still present in 3.0. Could be fixed in a more recent version. But if not, we need to fix that. I'll follow up.
That requirement might be due to android run-time permission support Requesting Permissions at Run Time as official document mention
Note: Beginning with Android 6.0 (API level 23), users can revoke permissions from any app at any time, even if the app targets a lower API level. You should test your app to verify that it behaves properly when it's missing a needed permission, regardless of what API level your app targets.
Currently it has been fixed with android studio 3.1 Canary 5
For instance app minimum API 23: Android 6.0 (Marshmallow).
Please follow this link https://developer.android.com/topic/instant-apps/getting-started/first-instant-app.html
来源：https://stackoverflow.com/questions/47687436/instant-app-whats-the-actual-minimum-sdk