ax-foundation-models

Foundation Models — On-Device AI for Apple Platforms

Quick Patterns

Basic Session

import FoundationModels

let session = LanguageModelSession(instructions: "You are a helpful assistant.")
let response = try await session.respond(to: userInput)
response.content // plain String

@Generable Structured Output

@Generable
struct Person {
    @Guide(description: "Full name")
    let name: String
    @Guide(.range(1...120))
    let age: Int
}

let response = try await session.respond(to: "Generate a person", generating: Person.self)
response.content // type-safe Person

Streaming

let stream = session.streamResponse(to: prompt, generating: Itinerary.self)
for try await partial in stream {
    self.itinerary = partial // PartiallyGenerated — all properties optional
}

Tool Calling

struct GetWeatherTool: Tool {
    let name = "getWeather"
    let description = "Retrieve latest weather for a city"

    @Generable
    struct Arguments {
        @Guide(description: "The city to fetch weather for")
        var city: String
    }

    func call(arguments: Arguments) async throws -> ToolOutput {
        let weather = try await WeatherService.shared.weather(for: /* geocoded location */)
        return ToolOutput("\(arguments.city): \(weather.currentWeather.temperature.value) degrees")
    }
}

let session = LanguageModelSession(tools: [GetWeatherTool()])

Availability Check (mandatory)

switch SystemLanguageModel.default.availability {
case .available:
    let session = LanguageModelSession()
case .unavailable(let reason):
    // Show: "AI features require Apple Intelligence"
}

Error Handling (mandatory)

do {
    let response = try await session.respond(to: prompt)
} catch LanguageModelSession.GenerationError.exceededContextWindowSize {
    session = condensedSession(from: session) // see Context Management
} catch LanguageModelSession.GenerationError.guardrailViolation {
    showMessage("I can't help with that request")
} catch LanguageModelSession.GenerationError.unsupportedLanguageOrLocale {
    showMessage("Language not supported")
}