[kevan]

The SDKs use Smithy[1] which is tailored for defining+generating services and SDKs, Ion is more of a pure data serialization format. It's definitely niche but my org uses it in a few places and it has some nice properties that fit our case pretty well (rapidly evolving schema, most clients only care about a small subset of attributes, ability to apply multiple and different schemas based on regions or businesses).

It's the sort of thing where I'd advise exploring other options first and only using it if the whys[2] really resonate with you because it definitely comes with some overhead.

[1] https://smithy.io/2.0/index.html [2] https://amazon-ion.github.io/ion-docs/guides/why.html