axiom-foundation-models-ref

Foundation Models Framework — Complete API Reference

Overview

The Foundation Models framework provides access to Apple's on-device Large Language Model (3 billion parameters, 2-bit quantized) with a Swift API. This reference covers every API, all WWDC 2025 code examples, and comprehensive implementation patterns.

Model Specifications

3B parameter model, 2-bit quantized, 4096 token context (input + output combined). Optimized for on-device summarization, extraction, classification, and generation. NOT suited for world knowledge, complex reasoning, math, or translation. Runs entirely on-device — no network, no cost, no data leaves device.

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When to Use This Reference

Use this reference when:

• Implementing Foundation Models features
• Understanding API capabilities
• Looking up specific code examples
• Planning architecture with Foundation Models
• Migrating from prototype to production
• Debugging implementation issues

Related Skills:

• axiom-foundation-models — Discipline skill with anti-patterns, pressure scenarios, decision trees
• axiom-foundation-models-diag — Diagnostic skill for troubleshooting issues

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LanguageModelSession

Overview

LanguageModelSession is the core class for interacting with the model. It maintains conversation history (transcript), handles multi-turn interactions, and manages model state.

Creating a Session

Basic Creation:

import FoundationModels

let session = LanguageModelSession()

With Custom Instructions:

let session = LanguageModelSession(instructions: """
    You are a friendly barista in a pixel art coffee shop.
    Respond to the player's question concisely.
    """
)

From WWDC 301:1:05

With Tools:

let session = LanguageModelSession(
    tools: [GetWeatherTool()],
    instructions: "Help user with weather forecasts."
)

From WWDC 286:15:03

With Specific Model/Use Case:

let session = LanguageModelSession(
    model: SystemLanguageModel(useCase: .contentTagging)
)