The Monolith with many endpoints use case.
Please check out this great talk One Monolith, Many Teams: Growing an Org with Elixir - Sofia Silva, André Albuquerque at ElixirConf 2026.
They don’t use Smithy, but - in theory - since Smithy is human readable, typed and even offers test generation - replacing OpenAPI YAML with nice Smithy models could help to standardize a complex platform.
The many clients for an Open Source project use case.
The OpenRiak database now offers a Smithy model for API v3.4 and generated clients for Python, Elixir and Erlang
Please check out the demos in f34nk/riak_clients to see how it works.
Since you are going to support Gleam, and there are also https://lfe.io/ and https://cure-lang.org and whatnot, would not make sense to provide the plugin architecture and treat other languages as plugins instead of hardcoded codegen directories?