Welcome to Android Central forums. I think you might be jumping the gun a little with these questions given Samsung hasn't officially announced the S26 series yet. Anything you're seeing right now are speculations mixed with rumor.
Having said all of that, just looking at Samsung's track record, there is going to be very little difference between the two devices. From last year to this, they took away more than they added if you ask me. Losing Bluetooth on the S-Pen, having the same sensor specs, not the same sensors, and a slightly better chip for more money, is not incentive to buy. I imagine next year they won't bring back BT for the S-Pen, the sensors will be the same or have the same specs and the chip will be imperceptibly better. Honestly when is the last time any of us looked at our device and thought this is noticeably slow or lagging? So, to me all of these marginal gains on the chip are worthless.
As far as AI goes, given they've turned One UI 8 into the One AI UI, I don't see them backing down on any of the AI add-on$, especially when/if they start charging for it. They can put it all behind a paywall and keep it as far as I'm concerned. Just like with this roll out, it started on this year's flagship but several of the previous year flagship devices are going to get exactly the same features and have the same experiences. I think there is one thing that the S25 can do that didn't get passed down to the other devices but I want to say they patched that so everyone has it now. I pretty sure they rolled AI out all way back to the S22 and to several budget models as well. There might be one or two things that some of them didn't get.
When they announce the S26 series there will be tons of comparison and review videos on YouTube to compare it to everything from a OnePlus to an 8-year-old S8 and so many others in-between. Keep your eyes on YouTube around Jan or Feb when Samsung holds it's electronic event and announces it's upcoming flagships and devices. but right after they announce there will be a flood of videos to answer all of your questions.
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