Hello Overlord1992
The difference between the Roomba 96X and the Roomba 98X are as follows:
The Roomba 98X has a more powerful battery which allows it to clean up to 185sqm. 120 minutes versus 90 minutes of cleaning time on one battery charge.
The Roomba 98X has the Carpet Power Boost which doubles the suction power on carpet, giving it 10 times the suction power of a 600 Series Roomba and twice the power of a Roomba 96X.
We hope to have helped you with this information and are happy to answer any further questions you may have.
Best regards
Your iRobot Team

In fact, I bought a Roomba981 last year and the Roomba976 last week as a gift.

In my opinion, the difference is the scope of delivery. The Roomba981 (the last number, the 1, is probably the colour) came with two barriers, a replacement filter and a replacement brush.

With the Roomba976 from last week there were no accessories. Only the charging station and the cable were included.

Needless to say, I am still absolutely satisfied with the performance of my Roomba981.