The chinease are working on two fifth generation projects
J20 which is big budget premier project specifically for chinease military
J31 which is lower end and will be for export market.
The j10 was their high end 4th generation fighter project which is avialable for export
The thunder was the lightweight low end project specifically designed for Pakistan.
If they are helping you further develope the thunder to add airframe improvements or better radars or ew suites etc that makes sense.
But those suggesting a massive redesigned thunder with internal weapons bays and fifth generuation technology are way off the mark and don't understand the huge complexity in changing a fighter.
If paf wants affordable low cost it will be thunders with minor improve ments.
If paf wants state of the art top end it will be j10 now until 2024 or j31 after this date
Anything else does not exist and is bordering fantasy which a senior guy like Oscar or mastan will confirm