It's a matter of processing power and programming.
Seed AI's are programmed different - they can recursively improve themselves. So they're already really freaking smart, then they make improvements to themselves, and they make themselves even smarter. Seed AI's need gigantic supercomputer systems and datacenters to run on though - and such systems are verboten in Eclipse Phase except for a few corporations and governments, and they're protected just as much or moreso than nuclear silos and launch complexes are protected today.
AGI's are AI's that cannot recursively improve themselves like Seed AI's, and they run on much lower-tier hardware, like a desktop server. They're basically sentient computer programs. IIRC, they're designed around a neural network similar to the human brain.
AI's are basically just 'smart' computer programs/algorithms. Not sentient, but would be something like a car that can drive itself through a city, or a plane that can fly itself between airports and deal with storms and weather and such.