It was mandatory, and that was changed due to widespread outrage over Scoped Storage due to a successful misinformation campaign against it. That's what I was talking about here:
twitter.com/DanielMicay/st
It's still going to be mandatory, but it has been delayed by a year to R.
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Replying to @DanielMicay @Ishan_Ishana and 4 others
However, since the Scoped Storage model being mandatory has been delayed until the next major API level in Android R, apps can keep relying on the legacy storage model for an extra year and users will have a worse experience with those apps with the feature enabled universally.
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