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Foundry Local C# SDK

The Foundry Local C# SDK provides a .NET interface for running AI models locally via the Foundry Local Core. Discover, download, load, and run inference entirely on your own machine — no cloud required.

Features

  • Model catalog — browse and search all available models; filter by cached or loaded state
  • Lifecycle management — download, load, unload, and remove models programmatically
  • Chat completions — synchronous and IAsyncEnumerable streaming via OpenAI-compatible types
  • Audio transcription — transcribe audio files with streaming support
  • Download progress — wire up an Action<float> callback for real-time download percentage
  • Model variants — select specific hardware/quantization variants per model alias
  • Optional web service — start an OpenAI-compatible REST endpoint (/v1/chat_completions, /v1/models)
  • WinML acceleration — opt-in Windows hardware acceleration with automatic EP download
  • Full async/await — every operation supports CancellationToken and async patterns
  • IDisposable — deterministic cleanup of native resources

Installation

dotnet add package Microsoft.AI.Foundry.Local

Building from source

cd sdk/cs
dotnet build src/Microsoft.AI.Foundry.Local.csproj

Or open Microsoft.AI.Foundry.Local.SDK.sln in Visual Studio / VS Code.

WinML: Automatic Hardware Acceleration (Windows)

On Windows, Foundry Local can leverage WinML for GPU/NPU hardware acceleration via ONNX Runtime execution providers (EPs). EPs are large binaries downloaded on first use and cached for subsequent runs.

Install the WinML package variant instead:

dotnet add package Microsoft.AI.Foundry.Local.WinML

Or build from source with:

dotnet build src/Microsoft.AI.Foundry.Local.csproj /p:UseWinML=true

Triggering EP download

EP download can be time-consuming. Call EnsureEpsDownloadedAsync early (after initialization) to separate the download step from catalog access:

// Initialize the manager first (see Quick Start)
await FoundryLocalManager.CreateAsync(
    new Configuration { AppName = "my-app" },
    NullLogger.Instance);

await FoundryLocalManager.Instance.EnsureEpsDownloadedAsync();

// Now catalog access won't trigger an EP download
var catalog = await FoundryLocalManager.Instance.GetCatalogAsync();

If you skip this step, EPs are downloaded automatically the first time you access the catalog. Once cached, subsequent calls are fast.

Quick Start

using Microsoft.AI.Foundry.Local;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Abstractions;
using Betalgo.Ranul.OpenAI.ObjectModels.RequestModels;

// 1. Initialize the singleton manager
await FoundryLocalManager.CreateAsync(
    new Configuration { AppName = "my-app" },
    NullLogger.Instance);

// 2. Get the model catalog and look up a model
var catalog = await FoundryLocalManager.Instance.GetCatalogAsync();
var model = await catalog.GetModelAsync("phi-3.5-mini")
    ?? throw new Exception("Model 'phi-3.5-mini' not found in catalog.");

// 3. Download (if needed) and load the model
await model.DownloadAsync();
await model.LoadAsync();

// 4. Get a chat client and run inference
var chatClient = await model.GetChatClientAsync();
var response = await chatClient.CompleteChatAsync(new[]
{
    ChatMessage.FromUser("Why is the sky blue?")
});

Console.WriteLine(response.Choices![0].Message.Content);

// 5. Clean up
FoundryLocalManager.Instance.Dispose();

Usage

Initialization

FoundryLocalManager is an async singleton. Call CreateAsync once at startup:

await FoundryLocalManager.CreateAsync(
    new Configuration { AppName = "my-app" },
    loggerFactory.CreateLogger("FoundryLocal"));

Access it anywhere afterward via FoundryLocalManager.Instance. Check FoundryLocalManager.IsInitialized to verify creation.

Catalog

The catalog lists all models known to the Foundry Local Core:

var catalog = await FoundryLocalManager.Instance.GetCatalogAsync();

// List all available models
var models = await catalog.ListModelsAsync();
foreach (var m in models)
    Console.WriteLine($"{m.Alias} — {m.SelectedVariant.Info.DisplayName}");

// Get a specific model by alias
var model = await catalog.GetModelAsync("phi-3.5-mini")
    ?? throw new Exception("Model 'phi-3.5-mini' not found in catalog.");

// Get a specific variant by its unique model ID
var variant = await catalog.GetModelVariantAsync("phi-3.5-mini-generic-gpu-4")
    ?? throw new Exception("Variant 'phi-3.5-mini-generic-gpu-4' not found in catalog.");

// List models already downloaded to the local cache
var cached = await catalog.GetCachedModelsAsync();

// List models currently loaded in memory
var loaded = await catalog.GetLoadedModelsAsync();

Model Lifecycle

Each Model wraps one or more ModelVariant entries (different quantizations, hardware targets). The SDK auto-selects the best variant, or you can pick one:

// Check and select variants
Console.WriteLine($"Selected: {model.SelectedVariant.Id}");
foreach (var v in model.Variants)
    Console.WriteLine($"  {v.Id} (cached: {await v.IsCachedAsync()})");

// Switch to a different variant
model.SelectVariant(model.Variants[1]);

Download, load, and unload:

// Download with progress reporting
await model.DownloadAsync(progress =>
    Console.WriteLine($"Download: {progress:F1}%"));

// Load into memory
await model.LoadAsync();

// Unload when done
await model.UnloadAsync();

// Remove from local cache entirely
await model.RemoveFromCacheAsync();

Chat Completions

var chatClient = await model.GetChatClientAsync();

var response = await chatClient.CompleteChatAsync(new[]
{
    ChatMessage.FromSystem("You are a helpful assistant."),
    ChatMessage.FromUser("Explain async/await in C#.")
});

Console.WriteLine(response.Choices![0].Message.Content);

Streaming

Use IAsyncEnumerable for token-by-token output:

using var cts = new CancellationTokenSource();

await foreach (var chunk in chatClient.CompleteChatStreamingAsync(
    new[] { ChatMessage.FromUser("Write a haiku about .NET") }, cts.Token))
{
    Console.Write(chunk.Choices?[0]?.Delta?.Content);
}

Chat Settings

Tune generation parameters per client:

chatClient.Settings.Temperature = 0.7f;
chatClient.Settings.MaxTokens = 256;
chatClient.Settings.TopP = 0.9f;
chatClient.Settings.FrequencyPenalty = 0.5f;

Audio Transcription

var audioClient = await model.GetAudioClientAsync();

// One-shot transcription
var result = await audioClient.TranscribeAudioAsync("recording.mp3");
Console.WriteLine(result.Text);

// Streaming transcription
await foreach (var chunk in audioClient.TranscribeAudioStreamingAsync("recording.mp3", CancellationToken.None))
{
    Console.Write(chunk.Text);
}

Audio Settings

audioClient.Settings.Language = "en";
audioClient.Settings.Temperature = 0.0f;

Live Audio Transcription (Real-Time Streaming)

For real-time microphone-to-text transcription, use CreateLiveTranscriptionSession(). Audio is pushed as raw PCM chunks and transcription results stream back as an IAsyncEnumerable.

The streaming result type (LiveAudioTranscriptionResponse) extends AudioCreateTranscriptionResponse from the Betalgo OpenAI SDK, so it's compatible with the file-based transcription output format while adding streaming-specific fields.

var audioClient = await model.GetAudioClientAsync();
var session = audioClient.CreateLiveTranscriptionSession();

// Configure audio format (must be set before StartAsync)
session.Settings.SampleRate = 16000;
session.Settings.Channels = 1;
session.Settings.Language = "en";

await session.StartAsync();

// Push audio from a microphone callback (thread-safe)
waveIn.DataAvailable += (sender, e) =>
{
    _ = session.AppendAsync(new ReadOnlyMemory<byte>(e.Buffer, 0, e.BytesRecorded));
};

// Read transcription results as they arrive
await foreach (var result in session.GetTranscriptionStream())
{
    // result follows the OpenAI Realtime ConversationItem pattern:
    // - result.Content[0].Text       — incremental transcribed text (per chunk, not accumulated)
    // - result.Content[0].Transcript — alias for Text (OpenAI Realtime compatibility)
    // - result.IsFinal               — true for final results, false for interim hypotheses
    // - result.StartTime / EndTime   — segment timing in seconds
    Console.Write(result.Content?[0]?.Text);
}

await session.StopAsync();

Output Type

Field Type Description
Content List<TranscriptionContentPart> Content parts. Access text via Content[0].Text or Content[0].Transcript.
IsFinal bool Whether this is a final or interim result. Nemotron always returns true.
StartTime double? Start time offset in the audio stream (seconds).
EndTime double? End time offset in the audio stream (seconds).
Id string? Unique identifier for this result (if available).

Session Lifecycle

Method Description
StartAsync() Initialize the streaming session. Settings are frozen after this call.
AppendAsync(pcmData) Push a chunk of raw PCM audio. Thread-safe (bounded internal queue).
GetTranscriptionStream() Async enumerable of transcription results.
StopAsync() Signal end-of-audio, flush remaining audio, and clean up.
DisposeAsync() Calls StopAsync if needed. Use await using for automatic cleanup.

Web Service

Start an OpenAI-compatible REST endpoint for use by external tools or processes:

// Configure the web service URL in your Configuration
await FoundryLocalManager.CreateAsync(
    new Configuration
    {
        AppName = "my-app",
        Web = new Configuration.WebService { Urls = "http://127.0.0.1:5000" }
    },
    NullLogger.Instance);

await FoundryLocalManager.Instance.StartWebServiceAsync();
Console.WriteLine($"Listening on: {string.Join(", ", FoundryLocalManager.Instance.Urls!)}");

// ... use the service ...

await FoundryLocalManager.Instance.StopWebServiceAsync();

Configuration

Property Type Default Description
AppName string (required) Your application name
AppDataDir string? ~/.{AppName} Application data directory
ModelCacheDir string? {AppDataDir}/cache/models Where models are stored locally
LogsDir string? {AppDataDir}/logs Log output directory
LogLevel LogLevel Warning Verbose, Debug, Information, Warning, Error, Fatal
Web WebService? null Web service configuration (see below)
AdditionalSettings IDictionary<string, string>? null Extra key-value settings passed to Core

Configuration.WebService

Property Type Default Description
Urls string? 127.0.0.1:0 Bind address; semi-colon separated for multiple
ExternalUrl Uri? null URI for accessing the web service in a separate process

Disposal

FoundryLocalManager implements IDisposable. Dispose stops the web service (if running) and releases native resources:

FoundryLocalManager.Instance.Dispose();

API Reference

Auto-generated API docs live in docs/api/. See GENERATE-DOCS.md to regenerate.

Key types:

Type Description
FoundryLocalManager Singleton entry point — create, catalog, web service
Configuration Initialization settings
ICatalog Model catalog interface
Model Model with variant selection
ModelVariant Specific model variant (hardware/quantization)
OpenAIChatClient Chat completions (sync + streaming)
OpenAIAudioClient Audio transcription (sync + streaming)
LiveAudioTranscriptionSession Real-time audio streaming session
LiveAudioTranscriptionResponse Streaming transcription result (ConversationItem-shaped)
ModelInfo Full model metadata record

Tests

dotnet test

See test/FoundryLocal.Tests/LOCAL_MODEL_TESTING.md for prerequisites and local model setup.