One premium smartphone feature that OnePlus only recently started including is an official IP rating for dust and water resistance. In fact, so far only the OnePlus 8 Pro has such a rating, but it looks like the OnePlus 9 Pro will be the second model to.

Common sense suggests it would, since it’s unlikely OnePlus would remove the feature, but now Max Jambor (a leaker with a reasonable track record) has specifically said that the OnePlus 9 Pro will have the same IP68 rating as the OnePlus 8 Pro.
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https://www.techradar.com/news/oneplus-9-range-is-likely-to-have-a-water-resistance-rating-but-only-on-one-model