Add APIs for denoting model availability

Sources/AnyLanguageModel/Availability.swift

@@ -0,0 +1,12 @@
+/// The availability status for a specific language model.
+public enum Availability<UnavailableReason> {
+    /// The model is ready for making requests.
+    case available
+
+    /// Indicates that the model is not ready for requests.
+    case unavailable(UnavailableReason)
+}
+
+extension Availability: Equatable where UnavailableReason: Equatable {}
+extension Availability: Hashable where UnavailableReason: Hashable {}
+extension Availability: Sendable where UnavailableReason: Sendable {}

Sources/AnyLanguageModel/LanguageModel.swift

@@ -1,6 +1,10 @@
 import Foundation
 
 public protocol LanguageModel: Sendable {
+    associatedtype UnavailableReason
+
+    var availability: Availability<UnavailableReason> { get }
+
     func prewarm(
         for session: LanguageModelSession,
         promptPrefix: Prompt?
@@ -33,6 +37,14 @@ public protocol LanguageModel: Sendable {
 // MARK: - Default Implementation
 
 extension LanguageModel {
+    public var isAvailable: Bool {
+        if case .available = availability {
+            return true
+        } else {
+            return false
+        }
+    }
+
     public func prewarm(
         for session: LanguageModelSession,
         promptPrefix: Prompt? = nil
@@ -49,3 +61,9 @@ extension LanguageModel {
         return Data()
     }
 }
+
+extension LanguageModel where UnavailableReason == Never {
+    public var availability: Availability<UnavailableReason> {
+        return .available
+    }
+}

Sources/AnyLanguageModel/Models/AnthropicLanguageModel.swift

@@ -28,6 +28,10 @@ import OrderedCollections
 /// )
 /// ```
 public struct AnthropicLanguageModel: LanguageModel {
+    /// The reason the model is unavailable.
+    /// This model is always available.
+    public typealias UnavailableReason = Never
+
     /// The default base URL for Anthropic's API.
     public static let defaultBaseURL = URL(string: "https://api.anthropic.com")!
 

Sources/AnyLanguageModel/Models/CoreMLLanguageModel.swift

@@ -19,6 +19,10 @@
     /// ```
     @available(macOS 15.0, iOS 18.0, tvOS 18.0, visionOS 2.0, watchOS 11.0, *)
     public struct CoreMLLanguageModel: AnyLanguageModel.LanguageModel {
+        /// The reason the model is unavailable.
+        /// This model is always available.
+        public typealias UnavailableReason = Never
+
         private let model: Models.LanguageModel
         private let tokenizer: any Tokenizer
         private let chatTemplateHandler: (@Sendable (Instructions?, Prompt) -> [Message])?

Sources/AnyLanguageModel/Models/LlamaLanguageModel.swift

@@ -13,6 +13,10 @@ import Foundation
     /// )
     /// ```
     public final class LlamaLanguageModel: LanguageModel, @unchecked Sendable {
+        /// The reason the model is unavailable.
+        /// This model is always available.
+        public typealias UnavailableReason = Never
+
         /// The path to the GGUF model file.
         public let modelPath: String
 

Sources/AnyLanguageModel/Models/MLXLanguageModel.swift

@@ -12,6 +12,10 @@ import Foundation
     /// let model = MLXLanguageModel(modelId: "mlx-community/Llama-3.2-3B-Instruct-4bit")
     /// ```
     public struct MLXLanguageModel: LanguageModel {
+        /// The reason the model is unavailable.
+        /// This model is always available.
+        public typealias UnavailableReason = Never
+
         /// The model identifier from the MLX community on Hugging Face.
         public let modelId: String
 

Sources/AnyLanguageModel/Models/OllamaLanguageModel.swift

@@ -14,6 +14,10 @@ import OrderedCollections
 /// let model = OllamaLanguageModel(model: "qwen2.5")
 /// ```
 public struct OllamaLanguageModel: LanguageModel {
+    /// The reason the model is unavailable.
+    /// This model is always available.
+    public typealias UnavailableReason = Never
+
     /// The default base URL for Ollama.
     public static let defaultBaseURL = URL(string: "http://localhost:11434")!
 

Sources/AnyLanguageModel/Models/OpenAILanguageModel.swift

@@ -17,6 +17,10 @@ import JSONSchema
 /// )
 /// ```
 public struct OpenAILanguageModel: LanguageModel {
+    /// The reason the model is unavailable.
+    /// This model is always available.
+    public typealias UnavailableReason = Never
+
     /// The default base URL for OpenAI's API.
     public static let defaultBaseURL = URL(string: "https://api.openai.com/v1/")!
 

Sources/AnyLanguageModel/Models/SystemLanguageModel.swift

@@ -12,9 +12,17 @@
     /// let model = SystemLanguageModel()
     /// ```
     @available(macOS 26.0, iOS 26.0, watchOS 26.0, tvOS 26.0, visionOS 26.0, *)
-    public struct SystemLanguageModel {
+    public struct SystemLanguageModel: LanguageModel {
+        /// The reason the model is unavailable.
+        public typealias UnavailableReason = FoundationModels.SystemLanguageModel.Availability.UnavailableReason
+
         let systemModel: FoundationModels.SystemLanguageModel
 
+        /// The default system language model.
+        public static var `default`: SystemLanguageModel {
+            SystemLanguageModel()
+        }
+
         /// Creates the default system language model.
         public init() {
             self.systemModel = FoundationModels.SystemLanguageModel.default
@@ -44,31 +52,15 @@
         ) {
             self.systemModel = FoundationModels.SystemLanguageModel(adapter: adapter, guardrails: guardrails)
         }
-    }
-
-    @available(macOS 26.0, iOS 26.0, watchOS 26.0, tvOS 26.0, visionOS 26.0, *)
-    extension SystemLanguageModel: LanguageModel {
-        public func logFeedbackAttachment(
-            within session: LanguageModelSession,
-            sentiment: LanguageModelFeedback.Sentiment?,
-            issues: [LanguageModelFeedback.Issue],
-            desiredOutput: Transcript.Entry?
-        ) -> Data {
-            let fmSession = FoundationModels.LanguageModelSession(
-                model: systemModel,
-                tools: session.tools.toFoundationModels(),
-                instructions: session.instructions?.toFoundationModels()
-            )
 
-            let fmSentiment = sentiment?.toFoundationModels()
-            let fmIssues = issues.map { $0.toFoundationModels() }
-            let fmDesiredOutput: FoundationModels.Transcript.Entry? = nil
-
-            return fmSession.logFeedbackAttachment(
-                sentiment: fmSentiment,
-                issues: fmIssues,
-                desiredOutput: fmDesiredOutput
-            )
+        /// The availability status for the system language model.
+        public var availability: Availability<UnavailableReason> {
+            switch systemModel.availability {
+            case .available:
+                .available
+            case .unavailable(let reason):
+                .unavailable(reason)
+            }
         }
 
         public func respond<Content>(
@@ -187,6 +179,30 @@
 
             return LanguageModelSession.ResponseStream(stream: stream)
         }
+
+        public func logFeedbackAttachment(
+            within session: LanguageModelSession,
+            sentiment: LanguageModelFeedback.Sentiment?,
+            issues: [LanguageModelFeedback.Issue],
+            desiredOutput: Transcript.Entry?
+        ) -> Data {
+            let fmSession = FoundationModels.LanguageModelSession(
+                model: systemModel,
+                tools: session.tools.toFoundationModels(),
+                instructions: session.instructions?.toFoundationModels()
+            )
+
+            let fmSentiment = sentiment?.toFoundationModels()
+            let fmIssues = issues.map { $0.toFoundationModels() }
+            let fmDesiredOutput: FoundationModels.Transcript.Entry? = nil
+
+            return fmSession.logFeedbackAttachment(
+                sentiment: fmSentiment,
+                issues: fmIssues,
+                desiredOutput: fmDesiredOutput
+            )
+        }
+
     }
 
     // MARK: - Helpers

Tests/AnyLanguageModelTests/MockLanguageModelTests.swift

@@ -48,4 +48,15 @@ struct MockLanguageModelTests {
             #expect(response.content == expected)
         }
     }
+
+    @Test func unavailable() async throws {
+        let model = MockLanguageModel.unavailable
+        let session = LanguageModelSession(model: model)
+
+        #expect(model.availability == .unavailable(.custom("MockLanguageModel is unavailable")))
+        #expect(model.isAvailable == false)
+
+        let response = try await session.respond(to: "Say hello")
+        #expect(response.content == "MockLanguageModel is unavailable")
+    }
 }

Tests/AnyLanguageModelTests/Shared/MockLanguageModel.swift

@@ -1,16 +1,26 @@
 @testable import AnyLanguageModel
 
 struct MockLanguageModel: LanguageModel {
+    enum UnavailableReason: Hashable, Sendable {
+        case custom(String)
+    }
+
+    var availabilityProvider: @Sendable () -> Availability<UnavailableReason>
     var responseProvider: @Sendable (Prompt, GenerationOptions) async throws -> String
 
     init(
-        responseProvider:
+        _ responseProvider:
             @escaping @Sendable (Prompt, GenerationOptions) async throws ->
             String = { _, _ in "Mock response" }
     ) {
+        self.availabilityProvider = { .available }
         self.responseProvider = responseProvider
     }
 
+    var availability: Availability<UnavailableReason> {
+        return availabilityProvider()
+    }
+
     func respond<Content>(
         within session: LanguageModelSession,
         to prompt: Prompt,
@@ -68,4 +78,10 @@ extension MockLanguageModel {
     static func fixed(_ response: String) -> Self {
         MockLanguageModel { _, _ in response }
     }
+
+    static var unavailable: Self {
+        var model = MockLanguageModel()
+        model.availabilityProvider = { .unavailable(.custom("MockLanguageModel is unavailable")) }
+        return model
+    }
 }

Tests/AnyLanguageModelTests/SystemLanguageModelTests.swift

@@ -1,11 +1,10 @@
 import Testing
-
-@testable import AnyLanguageModel
+import AnyLanguageModel
 
 #if canImport(FoundationModels)
     private let isSystemLanguageModelAvailable = {
         if #available(macOS 26.0, *) {
-            return SystemLanguageModel().systemModel.isAvailable
+            return SystemLanguageModel.default.isAvailable
         } else {
             return false
         }