Foundation Models

Overview

Foundation Models is Apple's generative-AI framework for intelligent app features. You drive a language model through a LanguageModelSession — generating text, structuring output into Swift types with guided generation (@Generable, GenerationSchema), and letting the model call your own Tools during generation. The default backend is the system language model (SystemLanguageModel), which runs on Apple Intelligence (iPhone, iPad, and Mac with Apple silicon). The same session API also targets Private Cloud Compute (PrivateCloudComputeLanguageModel, server-side) or a custom language model provider, so session code is portable across backends.

Before any feature, gate on availability — the model can be unavailable for several reasons:

private var model = SystemLanguageModel.default

switch model.availability {
case .available:
    // Show your intelligence UI.
case .unavailable(.deviceNotEligible):
    // Device can't run the model; offer an alternative.
case .unavailable(.appleIntelligenceNotEnabled):
    // Ask the person to turn on Apple Intelligence.
case .unavailable(.modelNotReady):
    // Still downloading or otherwise not ready.
case .unavailable(let other):
    // Other system reason.
}

Essentials

Create a session and respond to a prompt. respond(to:) is async and throws.

let session = LanguageModelSession()
let response = try await session.respond(to: "Write a profile for a dog breed.")
print(response.content)

Instructions give the session persistent behavior; GenerationOptions (e.g. temperature) tunes sampling; ContextOptions manages the context window:

let session = LanguageModelSession(instructions: """
    Suggest five related topics. Keep them concise (three to seven words).
    """)

let response = try await session.respond(to: "Making homemade bread")

// More creative sampling.
let session2 = LanguageModelSession()
let r = try await session2.respond(
    to: "Write me a story about coffee.",
    options: GenerationOptions(temperature: 1.0)
)

Use LanguageModelSession(model:) to target a backend, and the session's streaming API to receive output incrementally for long generations.

Structured Output (Guided Generation)

Generate typed data instead of free text. For primitives, pass the type directly:

let r = try await session.respond(to: "How many tablespoons are in a cup?",
                                  generating: Float.self)

For custom types, conform to Generable and guide fields with @Guide (supports constraints such as .range(...)):

@Generable(description: "Basic profile information about a cat")
struct CatProfile {
    var name: String

    @Guide(description: "The age of the cat", .range(0...20))
    var age: Int

    @Guide(description: "A one sentence profile about the cat's personality")
    var profile: String
}

let r = try await session.respond(to: "Generate a cute rescue cat",
                                  generating: CatProfile.self)

For schemas built at runtime, assemble DynamicGenerationSchema nodes into a GenerationSchema, then pass schema::

let menuSchema = DynamicGenerationSchema(
    name: "Menu",
    properties: [
        DynamicGenerationSchema.Property(
            name: "dailySoup",
            schema: DynamicGenerationSchema(
                name: "dailySoup",
                anyOf: ["Tomato", "Chicken Noodle", "Clam Chowder"]
            )
        )
        // Add additional properties.
    ]
)

let schema = try GenerationSchema(root: menuSchema, dependencies: [])
let r = try await session.respond(to: "What is today's menu?", schema: schema)

Tool Calling

Let the model invoke your code during generation. Conform to Tool; describe arguments with @Generable and return simple, model-friendly content from call(arguments:):

struct BreadDatabaseTool: Tool {
    let name = "searchBreadDatabase"
    let description = "Searches a local database for bread recipes."

    @Generable struct Arguments {
        @Guide(description: "The type of bread to search for")
        var searchTerm: String

        @Guide(description: "The number of recipes to get", .range(1...6))
        var limit: Int
    }

    func call(arguments: Arguments) async throws -> [String] {
        // Retrieve recipes from your database, then return formatted strings.
        return []
    }
}

let session = LanguageModelSession(tools: [BreadDatabaseTool()])
let r = try await session.respond(to: "Find three sourdough bread recipes")

Choosing a Backend

SystemLanguageModel.default — on-device, Apple Intelligence. Private and offline-capable; the default for most features.
PrivateCloudComputeLanguageModel — same session API, runs server-side on Apple's cloud. Requires the com.apple.developer.private-cloud-compute entitlement. Use when you need a larger cloud model; reuse your existing session code.
Custom language model provider — bring your own model behind the same session API.

Attach images with Attachment / ImageAttachmentContent for multimodal prompting and image analysis.

Checklist

Check SystemLanguageModel.default.availability; provide a fallback for each case.
Use LanguageModelSession, with instructions: for persistent guidance.
Prefer guided generation (@Generable / @Guide or GenerationSchema) over parsing free text.
Constrain numeric fields with @Guide ranges; validate generated values.
Expose app capabilities as Tools that return simple, model-friendly content.
Pick the backend deliberately: system vs Private Cloud Compute vs custom provider.
Stream long responses and manage the context window with ContextOptions.
Evaluate prompts and responses, and apply safety guidance for generative output.

Related skills

apple-intelligence — the participation layer (Siri, Spotlight, Writing Tools, Image Playground) that surrounds on-device generation.
core-ai — running your own model files (.aimodel) at the tensor level, for features that are not language-model shaped.

Resources

Apple — Foundation Models: https://developer.apple.com/documentation/foundationmodels
Generating content and performing tasks with Foundation Models
Generating Swift data structures with guided generation
Expanding generation with tool calling
Prefer Apple docs for up-to-date API details; web-search the current Foundation Models documentation alongside this skill.

foundation-models