This kind of exists, and here is one such system:

https://www.tandemdiabetes.com/products/t-slim-x2-insulin-pu...

The pump delivers insulin and gets blood glucose readings from a CGM (continuous glucose monitor) over bluetooth. Then the pump can make decisions such as stopping insulin delivery if you're going to go low, doing small correction boluses, and adjusting basal rate.

However it's far from perfect and still needs a lot of management. My wife has T1D and was recently pregnant, which really raises the bar on how tightly you need to control your diabetes. She ended up mostly micromanaging it all herself rather than trusting Control IQ to do the right thing.

The other issue is CGMs are not that accurate, so these systems are making decisions based on not great data.

I have a tandem pump. The problem I see is that you still have to wait an hour for the insulin to take affect. And like you say, it’s based on CGM data which is not always accurate enough. Perhaps in the future there will be implants that deliver insulin in a more direct route, such as intravenous or intramuscular. That would also make an overdose more dangerous, though.

This is either in trial or already in distribution, it is essentially a metered insulin pump coupled with a continuous glucose monitor.

https://www.diabetes.org.uk/guide-to-diabetes/diabetes-techn...

There are systems that automatically deliver insulin, but I don’t know of anything that automatically delivers glucose. That would be convenient.