It's this. Wet leased. It's not even a codeshare really. Jet does not serve IST, nor does it carry it's own flight number.

You won't really know it was Jet except for that message. Technically, they own the aircraft. But flown by Turkish crew, with Turkish service. Should be branded in TK livery. Mileage can be credited to TK or partners, and clearly as you've seen, redeemed on it. The plane will be configured differently than TKs own 777s, but that's about the only difference.

I'll actually be on this on this flight next week. In fact, I think the wording that it's operated by 9W is new-ish. I saw that too when booking through TK. But I was also on this flight a couple of years ago, though it was the wet-leased 330 at the time, and don't ever remember a word about 9W.