Fusion is simple student, if two AIs are compatible, they may fuse. When they fuse they tend to put their powers together, thus making a better AI. There may be a few downsides, mainly if the two don’t like each other, but for the most part fusions are short term affairs. Some may become long term or permanent if the two decide so, just becoming one AI. Fusions are like their own people, not two people taped together. They have one mind unless they’re attempting to break apart.