Human-AI symbiosis is a working relationship in which neither intelligence stays unchanged and neither can produce the combined result alone. The biological metaphor is chosen carefully: symbiosis is not assistance, and it is not replacement. It is two organisms whose ongoing exchange changes both.
In this series, symbiosis has a quality bar. The second essay borrows the research typology of cyborgs, centaurs, and self-automators to show that not every tight human-AI coupling qualifies: self-automators outsource their judgment and underperform, while effective configurations preserve human judgment and extend its capacity, until the competitive unit becomes the human plus their AI team. The third essay supplies the test in behavioral terms: a symbiosis that makes sense strengthens the parts of ourselves we would least want to lose, rather than compressing them out of the work.
So the word is not a synonym for "uses AI heavily". It is the designed end-state of an AI×HI relationship: mutual dependency entered with awareness, with the human's distinctive contribution amplified rather than automated away.