Though it is never specifically mentioned, Deep Winter seems to have replaced Eternal Spring when the "smart" AI "died" in 2537. Deep Winter was a 5th generation "smart" AI, which may possess longer life spans than previous generations of UNSC AI, or a "dumb AI", as it seems he lived from 2537 until 2551, double the number of years a 3rd generation smart AI lives.
Deep Winter was known to be very talkative. He seemed to enjoy the company of Kurt-051, SCPO Franklin Mendez and the SPARTAN-IIIs at Camp Currahee. Deep Winter also showed great concern for the young Spartans and often acted in what he thought to be their best interest, even when not ordered to do so. He monitored the progress and actions of the Beta Company Spartans even after they graduated and then monitored the progress of the Gamma Company Spartans as well. In 2551, he discovered the illegal drugs used in the augmentation process of the Gammas and tried to warn Kurt-051 via a secret Slipspace COM launcher. He was shut down soon after, as he had reached the end of his operational lifespan, but left files for Kurt to trace the source of the drugs. Ironically, Kurt was the one who was responsible for the illegal drugs, and he promptly had the files erased. They both thought they had done what was best for the Spartan-IIIs.
- Deep Winter and Endless Summer are said to be roundabout opposites to themselves in both personalities and mannerisms, considering the adjacent seasons in the real world, both Summer and Winter.
- Halo: Ghosts of Onyx (First appearance)