Quote comes from a recent Famitsu interview, translation comes from a Siliconera article:
I know that there were a lot of rumors about Sony implementing this, so I figured this deserved a thread.
【PS5】PS4の互換性率は99%! 転売対策もアリ? SIE社長 ジム・ライアン氏にプレイステーション5についてインタビュー | ゲーム・エンタメ最新情報のファミ通.com
発売日や値段も公開されたプレイステーション5(PS5)について、SIE社長 ジム・ライアン氏にインタビュー。
www.famitsu.com
Jim Ryan Confirmed PS5 Won't Have Compatibility With PS3 and Older Games
In a Japanese interview with Famitsu, SIE CEO Jim Ryan confirmed that PS5 won't have backwards compatibility with PS3 and older games.
www.siliconera.com
Famitsu: We were also surprised when we heard that it will have 99% compatibility with PS4 titles. By the way, will there be compatibility with PS1, PS2, and PS3 titles?
Jim Ryan: We keep in mind the engineering specialized for the PS5, as we produced the device. In the midst of that, the PS4 already has 100 million players; we thought they ought to want to play PS4 titles on the PS5 as well indeed, so we included compatibility with the PS4. While implementing that, we also focused our efforts on taking in the high-speed SSD and the new controller DualSense at the same time. So, unfortunately, we couldn't reach the implementation of such compatibilities.
I know that there were a lot of rumors about Sony implementing this, so I figured this deserved a thread.