From the Native histograms spec:

As usual, PromQL implementations MAY apply any optimizations they see fit as long as the behavior stays the same. Decoding native histograms can be quite expensive with the potentially many buckets. Similarly, deep-copying a histogram sample within the PromQL engine is much more expensive than copying a simple float sample. This creates a huge potential for optimization compared to a naive approach of always decoding everything and always copying everything.

Prometheus currently tries to avoid needless copies (TODO: but a proper CoW like approach still has to be implemented, as it would be much cleaner and less bug prone) and skips decoding of the buckets for special cases where only the sum and count of observations is required.

Implement a generic high performance framework for handling copy-on-write and pooling of native histogram samples.

Related PR: #13679 where I tried to handle a sub-case, but it turned out to be way too complicated.