Comment by tonyoconnell

What it is

Apple's Foundation Models framework (shipping in iOS 27 / macOS 27 this fall) is the standard Swift API for on-device AI — the same API Apple uses for their own small model. This package makes Claude plug into that same API as a drop-in swap.

  // Apple's on-device model
  let session = LanguageModelSession(model: SystemLanguageModel.default)

  // Claude — same API, just different model constructor
  let session = LanguageModelSession(model: ClaudeLanguageModel(name: .sonnet4_6, auth: auth))

One API, two tiers. You write your app once against the Foundation Models protocol. On-device model handles fast/free/private tasks; Claude handles heavy reasoning, long context, or capability gaps — you swap the model, not your code.

You don't call the Anthropic API directly. Apple's framework handles streaming, tool calling, and structured output (@Generable) — you just get Claude's capability through it.