I just noticed a word changed in GIEP plan versions:
ability grouping with intellectual peers
was changed to
cluster grouping with intellectual peers.
Does one refer to a more intellectually narrow classroom grouping or do they mean the same thing?

I would understand "ability grouping" as a self contained group with more organizational and curricular separation, and "cluster grouping" as putting several similar kids together in one heterogeneous classroom with lots of other kids, with curricular differentiation happening as much or as little as it happens for everyone.
You may want to google Susan Wjnebrenner to find out about he research on making cluster grouping successful.

I'd also add that what a term means in reality vs what it means to the people who are using it and instructing based on it can be two very different things I'd ask the person (or team) who wrote the IEP to define exactly what "cluster grouping" means to them - and then get very specific about writing it out in the IEP. If it's something that you think is a *good* practice for your child and it's not clearly defined, then I'd suggest you write out your understanding of it in the parent comments section of the IEP. If it's something you're concerned about, address it.

Best wishes,

polarbear

Each group is relating to grouping for small group work/practice of curriculum instruction. I didn't know if it had to do with ability grouping being a closer intellectual grouping and cluster grouping being a looser peer grouping. School has already told me there isn't a good peer group in grade and can't meet needs within current classroom setting even with GIEP. I was curious if the ability to cluster change was coming from them releasing themselves of need to address child's actual needs vs just getting in the ballpark?

You've received great responses above. I'll just add that many gifted education program and service terms have fuzzy, nebulous meanings and are essentially buzzwords.

I would definitely ask for clarification on what the change in terminology means in terms of what your child will experience.

This is silly. Who do they want to cluster your child with if there are no gifted peers?