The boy built Simon when he was eight. Simon grew up with him. Now Simon is the only thing keeping him human.

Eli Kane is a seventeen-year-old genius raised by his late grandfather - a neuroscientist whose government-funded chip was supposed to heal injured soldiers from the inside. Eli has another idea. He implants the chip on himself.

What he gets is unbearable clarity: the heart rates of strangers, the chemistry of fear, the precise moment a lie leaves a mouth. What he loses is harder to name. The shyness. The awkwardness. The boyfriend his girlfriend fell for in the first place. Everyone else says he is finally come out of his shell. She is the only one who notices someone she loved is gone.

Simon notices too.

Simon is the AI Eli has been building since childhood - not a superintelligence, not a chatbot, but a sibling. Simon learned what Eli learned. Simon heard what Eli heard. Simon was built to serve the boy. Now Simon job is to save him from what the boy is becoming - while the government that funded the chip research realizes what it can really do, and comes for it.

Simon X/O is a story about enhancement and erosion, about a love that survives a person who does not, and about the strange grace of being remembered by a machine that refuses to forget who you used to be.

For readers of Ready Player One, The Maze Runner, and Scythe - but with a soul that belongs to nobody else.