foundation-models

Safe, idiomatic Rust bindings for Apple's FoundationModels framework — the on-device large language model that ships with Apple Intelligence on macOS 26+.

Features

• Sessions and multi-turn chat — create, restore, inspect, and persist LanguageModelSessions
• Streaming — text deltas and structured-generation snapshots
• Async API — executor-agnostic Future wrappers for respond(to:), respond(to:generating:), and adapter lifecycle (see async_api module)
• Tool calling — register Rust callbacks as FoundationModels Tools
• Structured generation — JSON-schema validation, dynamic schemas, string-choice schemas, array guides, explicit nil-representation helpers, and Rust Generable traits
• Structured content helpers — typed GenerationId, string-backed Decimal, GeneratedContentKind, and generated-content builders with optional IDs
• System model configuration — availability, use cases, guardrails, locales, adapter handles, and async token counting
• Transcript support — typed transcript inspection plus raw JSON round-tripping
• Response / tool definitions — ResponseFormat::generating, inferred Tool::generable, and transcript ToolDefinition helpers
• Typed error metadata — FMError accessors for recovery suggestions, refusal helpers, tool-call details, and generation/schema/adapter-error contexts
• Feedback attachments — full LanguageModelFeedback issue/sentiment support

Requirements

• macOS 26.0 or newer (build host and runtime)
• Xcode 26 SDK
• Apple Intelligence enabled in System Settings
• Apple Silicon

Installation

[dependencies]
foundation-models = { version = "0.11.2", features = ["macos_26_0"] }

Async API

Enable the async feature to get executor-agnostic Future wrappers that work with any async runtime (Tokio, async-std, smol, pollster, …):

[dependencies]
foundation-models = { version = "0.11.2", features = ["macos_26_0", "async"] }

use foundation_models::{LanguageModelSession, SystemLanguageModel};
#[cfg(feature = "async")]
use foundation_models::async_api::AsyncSession;

# fn main() -> Result<(), Box<dyn std::error::Error>> {
if !SystemLanguageModel::is_available() { return Ok(()); }
#[cfg(feature = "async")]
pollster::block_on(async {
    let session = LanguageModelSession::new();
    let reply = AsyncSession::new(&session).respond("Name three Norse gods.")?.await?;
    println!("{}", reply.content);
    Ok::<(), Box<dyn std::error::Error>>(())
})?;
# Ok(())
# }

Tier 2 note: LanguageModelSession.streamResponse(to:) is an AsyncSequence (multi-fire stream). It is deferred to Tier 2. Use LanguageModelSession::stream for synchronous streaming today.

Quick start

use foundation_models::prelude::*;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    if !SystemLanguageModel::is_available() {
        eprintln!("Unavailable: {:?}", SystemLanguageModel::availability());
        return Ok(());
    }

    let session = LanguageModelSession::with_instructions(
        "Answer in a single concise sentence.",
    );
    let reply = session.respond("Why is the sky blue?")?;
    println!("{reply}");
    Ok(())
}

Tool calling

use foundation_models::prelude::*;
use serde::Deserialize;

#[derive(Deserialize)]
struct EchoArgs {
    message: String,
}

# fn main() -> Result<(), Box<dyn std::error::Error>> {
let schema = GenerationSchema::from_dynamic(
    DynamicGenerationSchema::object("EchoArgs").with_property(
        "message",
        DynamicGenerationProperty::new(DynamicGenerationSchema::string()),
    ),
    [],
)?;

let tool = Tool::json("echo", "Echo the provided message.", schema, |args: EchoArgs| {
    Ok(args.message)
});

let session = LanguageModelSession::builder()
    .instructions("Use tools when explicitly asked.")?
    .tool(tool)
    .build()?;

let reply = session.respond_prompt(
    "Use the echo tool exactly once with the message 'hello from Rust'.",
)?;
println!("{reply}");
# Ok(())
# }

Structured generation

use foundation_models::prelude::*;

# fn main() -> Result<(), Box<dyn std::error::Error>> {
let schema = GenerationSchema::from_dynamic(
    DynamicGenerationSchema::object("Movie")
        .with_property(
            "title",
            DynamicGenerationProperty::new(DynamicGenerationSchema::string()),
        )
        .with_property(
            "year",
            DynamicGenerationProperty::new(DynamicGenerationSchema::integer()),
        ),
    [],
)?;

let session = LanguageModelSession::new();
let response = session.respond_generated(
    "Return JSON for one classic science-fiction movie.",
    &schema,
    true,
)?;
println!("{}", response.json_string()?);
# Ok(())
# }

Coverage-oriented helpers

use foundation_models::prelude::*;

# fn main() -> Result<(), Box<dyn std::error::Error>> {
let schema = GenerationSchema::from_dynamic(
    DynamicGenerationSchema::array_of(DynamicGenerationSchema::string()).with_guides([
        GenerationGuide::minimum_count(1),
        GenerationGuide::maximum_count(3),
        GenerationGuide::element(GenerationGuide::string_pattern("^[a-z]+$")),
    ]),
    [],
)?;

let response_format = ResponseFormat::generating::<GeneratedContent>()?;
let tool = Tool::generable("echo", "Echo structured content", |args: GeneratedContent| {
    Ok(args.json_string()?)
})?;

println!("{}", schema.json_schema());
println!("{}", response_format.name());
println!("{}", tool.definition().name);
# Ok(())
# }

Smoke example

cargo run --example 06_smoke --features macos_26_0
cargo run --example 07_schema_surface --features macos_26_0

Notes

• Swift-only compile-time macros such as @Generable and @Guide are exposed as Rust runtime traits/builders (Generable, GenerationGuide, DynamicGenerationSchema).
• The previously audited SystemLanguageModel.Adapter::isCompatible(_ assetPack:) exemption has been removed: Xcode 26.5's FoundationModels.swiftinterface no longer exposes that symbol. Enable the optional backgroundassets feature to pull in the sibling backgroundassets crate for future interop helpers.
• GenerationID now round-trips as GenerationId via GeneratedContent::generation_id_handle(); GeneratedContent::generation_id() remains as a best-effort string helper.
• Typed generation/schema/adapter error metadata plus refusal helpers are available through FMError::{generation_error_context, adapter_asset_error_context, schema_error_context, recovery_suggestion, failure_reason, refusal, tool_call_error}.
• Xcode 26.5's FoundationModels.swiftinterface does not expose standalone PromptTag, Conversation, ToolCallingMode, SystemPrompt, Examples, LanguageModelInputContent, LanguageModelOutputContent, or Streaming symbols; see COVERAGE.md for the audited matrix.

License

Licensed under either of Apache-2.0 or MIT at your option.