> There's clearly no intelligence task that AIs can't do due to some magic fundamental constraint.

Yes there is: write an English paragraph that doesn't make me want to claw my eyes out. LLMs are not better than human mathematicians (or security researchers) in all respects, just some specific ways (e.g. not having to take a lunch break) that make them good at exhaustively searching for an answer, given the right constraints.

> write an English paragraph that doesn't make me want to claw my eyes out.

LLMs are very much capable of that. Your belief in the opposite has two causes. Firstly the toupee fallacy. You don't notice LLM written text that doesn't make you claw your eyes out. Second is defaults. The huge majority of people who writes text with LLMs just uses default Claude/GPT models, and put near zero effort in making it sound human. Those models are indeed bad at it by default so they need a lot of effort to overcome it. In cases like Opus 5 it's near impossible to overcome. That doesn't generalize to "LLMs".

What's the fundamental constraint that will ensure this continues to be the case in a year, or five years?