GitHub Copilot SDK C# Instructions

Core Principles

• The SDK is in technical preview and may have breaking changes
• Requires .NET 10.0 or later
• Requires GitHub Copilot CLI installed and in PATH
• Uses async/await patterns throughout
• Implements IAsyncDisposable for resource cleanup

Installation

Always install via NuGet:

dotnet add package GitHub.Copilot.SDK

Client Initialization

Basic Client Setup

await using var client = new CopilotClient();
await client.StartAsync();

Client Configuration Options

When creating a CopilotClient, use CopilotClientOptions:

• CliPath - Path to CLI executable (default: "copilot" from PATH)
• CliArgs - Extra arguments prepended before SDK-managed flags
• CliUrl - URL of existing CLI server (e.g., "localhost:8080"). When provided, client won't spawn a process
• Port - Server port (default: 0 for random)
• UseStdio - Use stdio transport instead of TCP (default: true)
• LogLevel - Log level (default: "info")
• AutoStart - Auto-start server (default: true)
• AutoRestart - Auto-restart on crash (default: true)
• Cwd - Working directory for the CLI process
• Environment - Environment variables for the CLI process
• Logger - ILogger instance for SDK logging

Manual Server Control

For explicit control:

var client = new CopilotClient(new CopilotClientOptions { AutoStart = false });
await client.StartAsync();
// Use client...
await client.StopAsync();

Use ForceStopAsync() when StopAsync() takes too long.

Session Management

Creating Sessions

Use SessionConfig for configuration:

await using var session = await client.CreateSessionAsync(new SessionConfig
{
    Model = "gpt-5",
    Streaming = true,
    Tools = [...],
    SystemMessage = new SystemMessageConfig { ... },
    AvailableTools = ["tool1", "tool2"],
    ExcludedTools = ["tool3"],
    Provider = new ProviderConfig { ... }
});

Session Config Options

• SessionId - Custom session ID
• Model - Model name ("gpt-5", "claude-sonnet-4.5", etc.)
• Tools - Custom tools exposed to the CLI
• SystemMessage - System message customization
• AvailableTools - Allowlist of tool names
• ExcludedTools - Blocklist of tool names
• Provider - Custom API provider configuration (BYOK)
• Streaming - Enable streaming response chunks (default: false)