Just found they added a new initializer from a JSON string somewhere between the second and third beta. It's even better than I expected https://developer.apple.com/documentation/foundationmodels/generatedcontent/init(json:)

To explain a little why this might be useful: – It allows for more use cases of Foundation Models from non-native frameworks like Flutter and React Native. Here is an example of how you can create a bridge from Flutter to Foundation Models, with Dart Tools support. – It also opens up use cases like MCP servers, where tools are dynamically fetched from some config/server. Though not very usable given current model constraints — but still.

For anyone looking for a temporary solution, you can (but probably shouldn't) do this: struct DynamicKeyValuePairs<K, V> { let _elements: [(K, V)] init(_elements: [(K, V)]) { self._elements = _elements } } let kvp = unsafeBitCast( DynamicKeyValuePairs(_elements: properties), to: KeyValuePairs<String, any ConvertibleToGeneratedContent>.self )