In April, Detective Inspector Mike Foster said the boy was talking but still "very ill" and had months of rehabilitation ahead of him.
On Wednesday, Foster told 'Hawke's Bay Today' the boy was discharged from hospital "about two months ago" and was undergoing rehabilitation treatment at an Auckland rehab centre.
"He's making steady progress at rehabilitation," he said.
Foster said the boy's injuries were "so severe" that he would "sadly" be doing rehab for a long time.
He previously compared the boy's injuries to those suffered by James Whakaruru and said they were the worst he had seen in his 30-year career.
Foster said it was a complex case and while no arrests had been made to date, he was hopeful there would be a trial.
"It depends a lot on medical advice."
The boy is not living with extended whanau or other family members as other media reported, Foster said.
Alison McDonald, Oranga Tamariki deputy chief executive Children & Families South, told 'Hawke's Bay Today' the agency was helping with the boy's rehabilitation.
"The young boy is still at a rehabilitation centre and we are working with his extended family to determine the best care arrangements for his future," McDonald said.
"Oranga Tamariki has worked with health professionals during his recovery and rehabilitation and will continue to work alongside his extended family to help keep him safe and well when he is discharged."
The agency also said that while there was an active police investigation and Family Court proceedings under way, further comment could not be made on the case.
In April, Foster told 'Hawke's Bay Today' the entire case was not simply a matter of asking the boy who assaulted him, and then arresting them.
"It's a complex case. We'll make decisions on arrests once we have all the material in front of us and also once we have consulted with the Crown."
Oranga Tamariki had previously worked with the family in what was described as "challenging circumstances."
The boy was admitted to hospital on at least one other occasion, with injuries including broken bones.
Oranga Tamariki intervened and the boy was placed into the care of wider family and was returned to his immediate family shortly before Christmas, 2019.