# Apple Foundation Models

> Source: <https://platform.claude.com/docs/en/cli-sdks-libraries/libraries/apple-foundation-models>
> Published: 2026-06-15 04:55:34+00:00

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[Claude for Foundation Models](https://github.com/anthropics/ClaudeForFoundationModels) is a Swift package that makes Claude available as a server-side language model in Apple's [Foundation Models](https://developer.apple.com/documentation/foundationmodels) framework. The package conforms Claude to the framework's `LanguageModel`

protocol, so you drive it with the same `LanguageModelSession`

API you use for Apple's on-device model: `respond(to:)`

, streaming, guided generation, and tool calling all work the same way.

Requests go directly from your app to the Claude API; Apple is not in the request path and does not see prompts or responses. Usage is billed to your Anthropic account at [standard API pricing](/docs/en/about-claude/pricing). Your app decides when to use Claude and when to use Apple's on-device model: pass whichever model you want to each session.

**Beta.** This package targets the Foundation Models server-side language model API introduced in the OS 27 betas. APIs may change before general availability.

Claude for Foundation Models is **not** a general-purpose Messages API client. Its public surface is the Foundation Models provider conformance plus the configuration types that reach it (`ClaudeLanguageModel`

, `ClaudeModel`

, `AuthMode`

, `ClaudeServerTool`

). For direct access to the Messages API in another language, see the [Client SDKs](/docs/en/cli-sdks-libraries/overview#client-sdks).

Add the package to your `Package.swift`

:

```
dependencies: [
  .package(url: "https://github.com/anthropics/ClaudeForFoundationModels.git", from: "0.1.0")
]
```

Or in Xcode: **File** > **Add Package Dependencies…** and enter the repository URL.

Then add `ClaudeForFoundationModels`

to your target's dependencies and import it alongside `FoundationModels`

:

``` python
import FoundationModels
import ClaudeForFoundationModels
```

`ClaudeLanguageModel`

is the entry point. Pass it to `LanguageModelSession`

and use the session exactly as you would with any Foundation Models provider:

``` python
import FoundationModels
import ClaudeForFoundationModels

let model = ClaudeLanguageModel(
  name: .sonnet4_6,
  auth: .apiKey(ProcessInfo.processInfo.environment["ANTHROPIC_API_KEY"] ?? "")
)

let session = LanguageModelSession(model: model)
let response = try await session.respond(to: "Plan a 4-day trip to Buenos Aires.")
print(response.content)
```

The initializer also accepts `baseURL`

(default `https://api.anthropic.com`

), `timeout`

, and `serverTools`

(see [Server-side tools](#server-side-tools)).

For a complete working program, the repository includes [ Examples/ClaudeExample](https://github.com/anthropics/ClaudeForFoundationModels/tree/main/Examples/ClaudeExample), a runnable command-line target that streams a chat turn to the terminal, with a

`--search`

flag that enables server-side web search for the turn. Running it requires a macOS 27 host.Model identifiers are values of `ClaudeModel`

. Use a compiled-in constant, or construct one with explicit capabilities for an ID that isn't compiled in yet (see [Capabilities](#capabilities)):

```
ClaudeLanguageModel(name: .opus4_8, auth: auth)
```

Constants mirror API model IDs (`.opus4_8`

is `claude-opus-4-8`

) and carry each model's capabilities. New models ship as new constants in package releases; check `ClaudeModel`

in Xcode for the current list, and the [Models overview](/docs/en/about-claude/models/overview) to compare models.

Each `ClaudeModel`

declares what it accepts: sampling parameters, effort levels, adaptive thinking, structured output, and image input. The package uses this to decide which request fields to send, because sending a field a model rejects is a hard error. The constants carry the right capabilities. For an ID that isn't compiled in, declare what the model accepts (there is deliberately no shorthand that guesses):

``` js
let model = ClaudeModel(
  id: "claude-experimental-x",
  capabilities: .init(samplingParams: false, effortLevels: [.low, .high])
)
ClaudeLanguageModel(name: model, auth: auth)
```

Pin a Claude [effort level](/docs/en/build-with-claude/effort) for every request with `fixedEffort:`

. It takes precedence over the framework's per-request reasoning hints, and it's the only way to request `.xhigh`

or `.max`

, because the framework's reasoning levels stop at high. The API defaults to `high`

when no effort is sent:

```
ClaudeLanguageModel(name: .opus4_8, auth: auth, fixedEffort: .xhigh)
```

The level must be one the model accepts. Each `ClaudeModel`

declares which of the five levels (`low`

, `medium`

, `high`

, `xhigh`

, `max`

) its model takes, if any: some models don't accept effort at all.

Apple's on-device model is fast, private, and works offline, but it is sized for lightweight tasks. Escalate to Claude when you need larger context, frontier reasoning, or server-side tools such as web search and code execution. Because both use the same `LanguageModelSession`

API, you can switch by swapping the `model:`

argument.

Set the credential with the `auth:`

parameter.

Pass an API key directly while developing:

```
ClaudeLanguageModel(name: .sonnet4_6, auth: .apiKey("YOUR_API_KEY"))
```

A key bundled into an app is extractable from the shipping binary, and anyone who extracts it can make requests billed to your account. Use `.apiKey`

for development only, and switch to a proxy before release.

For production, route requests through your own back end with `.proxied`

. The relay at `baseURL`

adds the Claude API credential server-side, so the app ships no key. The `headers`

you provide are sent on every request so your proxy can authorize the caller. Pass `[:]`

if it needs none:

```
ClaudeLanguageModel(
  name: .sonnet4_6,
  auth: .proxied(headers: ["X-App-Token": "..."]),
  baseURL: URL(string: "https://api.yourapp.com/claude")!
)
```

Your proxy receives standard [Messages API](/docs/en/api/messages/create) requests, attaches the `x-api-key`

header, and forwards them to `https://api.anthropic.com`

.

`streamResponse(to:)`

returns the response incrementally. Each element is a cumulative snapshot of the response so far, not a delta:

``` js
let stream = session.streamResponse(to: "Summarize today's top science stories.")
for try await partial in stream {
  print(partial.content)
}
```

Annotate a type with `@Generable`

and request it with `generating:`

. The model returns a value of that type through [structured outputs](/docs/en/build-with-claude/structured-outputs):

``` js
@Generable
struct Trip {
  @Guide(description: "Destination city") var destination: String
  @Guide(description: "Length in days") var days: Int
}

let response = try await session.respond(to: "Plan a trip to Tokyo.", generating: Trip.self)
print(response.content.destination)
```

Structured output requires a model whose capabilities include it (all compiled-in constants do). If the chosen model does not, the package throws `LanguageModelError.unsupportedGenerationGuide`

rather than silently degrading.

The framework's `tools:`

array works unchanged. Conform your types to `Tool`

, pass them to `LanguageModelSession`

, and the framework invokes them on the device when Claude calls them. See [Tool use with Claude](/docs/en/agents-and-tools/tool-use/overview).

``` js
let session = LanguageModelSession(model: model, tools: [FindRestaurantsTool()])
```

[Server tools](/docs/en/agents-and-tools/tool-use/server-tools) (web search, web fetch, and code execution) run on Anthropic's infrastructure within a single round trip, with nothing for the framework to invoke on the device. Configure them per model with `serverTools:`

:

``` js
let model = ClaudeLanguageModel(
  name: .sonnet4_6,
  auth: auth,
  serverTools: [
    .webSearch(maxUses: 5),
    .codeExecution,
  ]
)
```

`.webSearch`

and `.webFetch`

accept optional `allowedDomains`

, `blockedDomains`

, and `maxUses`

. Server tool activity surfaces in the transcript as `ClaudeServerToolSegment`

custom segments.

`serverTools`

is configured on `ClaudeLanguageModel`

rather than on `LanguageModelSession`

because the session type is Apple's. To use different server-tool sets per conversation, construct multiple `ClaudeLanguageModel`

instances.

Models whose capabilities include image input declare the framework's vision capability. Pass image content through the framework's standard session API; the package converts it to the Claude API's image format. See [Vision](/docs/en/build-with-claude/vision) for image requirements.

The package maps Claude API errors onto Apple's `LanguageModelError`

cases where one fits: context-window overflow surfaces as `.contextSizeExceeded`

, HTTP 429 as `.rateLimited`

, a request past the configured timeout as `.timeout`

. Provider errors with no framework equivalent surface as `ClaudeError`

. Pattern-match to drive product flows:

``` js
do {
  let response = try await session.respond(to: prompt)
  print(response.content)
} catch ClaudeError.missingCredential {
  // Prompt for an API key.
} catch let error as LanguageModelError {
  // Framework-shaped errors (rate limits, guardrails, context length, decoding).
} catch {
  // Transport errors.
}
```

A common pattern is to catch `.rateLimited`

and fall back to `SystemLanguageModel`

for that turn, queue the request, or surface a retry affordance.

The package surfaces the Messages API capabilities that the Foundation Models provider protocol can express. Features with no representation in Apple's protocol are not available through it, including:

| Reference | Covers |
|---|---|
|

`LanguageModelSession`

, `@Generable`

, `Transcript`

, `Tool`

, and the rest of the framework surface`ClaudeForFoundationModels`

on GitHubThe package is licensed under Apache 2.0. Bug reports are welcome through GitHub issues. External pull requests are not being accepted during the beta period.

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