.NET: Add Anthropic Agent Package

[rogerbarreto]

Adding Anthropic AIAgent Support

Using offical Anthropic Package.

https://www.nuget.org/packages/Anthropic

• Unit Tests
• Integration Tests
• Extensions
• Samples

---

• Polyfill will be removed as soon new Anthropic Package releases with IChatClient support.

• Add Microsoft.Extensions.AI support anthropics/anthropic-sdk-csharp#10

cc: @stephentoub

[Copilot]

Pull Request Overview

This PR adds comprehensive support for Anthropic Claude models to the Microsoft Agent Framework, enabling developers to create AI agents using the official Anthropic SDK.

Key Changes:

• Integration with Anthropic SDK via polyfill extensions (to be replaced once upstream PR merges)
• Extension methods for creating agents from IAnthropicClient and IBetaService
• Support for advanced features including reasoning/thinking capabilities and function tools

Reviewed Changes

Copilot reviewed 34 out of 34 changed files in this pull request and generated 27 comments.

Show a summary per file

File	Description
dotnet/src/Microsoft.Agents.AI.Anthropic/Microsoft.Agents.AI.Anthropic.csproj	New project file for Anthropic agent support package
dotnet/src/Microsoft.Agents.AI.Anthropic/AnthropicClientExtensions.cs	Extension methods to create AI agents from IAnthropicClient
dotnet/src/Microsoft.Agents.AI.Anthropic/AnthropicBetaServiceExtensions.cs	Extension methods to create AI agents from IBetaService
dotnet/src/Microsoft.Agents.AI.Anthropic/AnthropicClientJsonContext.cs	JSON serialization context for Anthropic operations
dotnet/src/Microsoft.Agents.AI.Anthropic/External/AnthropicClientExtensions.cs	Polyfill implementation for IChatClient support (temporary)
dotnet/src/Microsoft.Agents.AI.Anthropic/External/AnthropicBetaClientExtensions.cs	Polyfill implementation for Beta service IChatClient support (temporary)
dotnet/tests/Microsoft.Agents.AI.Anthropic.UnitTests/Microsoft.Agents.AI.Anthropic.UnitTests.csproj	Unit test project configuration
dotnet/tests/Microsoft.Agents.AI.Anthropic.UnitTests/Extensions/AnthropicClientExtensionsTests.cs	Unit tests for IAnthropicClient extension methods
dotnet/tests/Microsoft.Agents.AI.Anthropic.UnitTests/Extensions/AnthropicBetaServiceExtensionsTests.cs	Unit tests for IBetaService extension methods
dotnet/tests/AnthropicChatCompletion.IntegrationTests/AnthropicChatCompletion.IntegrationTests.csproj	Integration test project configuration
dotnet/tests/AnthropicChatCompletion.IntegrationTests/AnthropicChatCompletionFixture.cs	Test fixture supporting both regular and reasoning models
dotnet/tests/AnthropicChatCompletion.IntegrationTests/AnthropicChatCompletionRunTests.cs	Integration tests for agent runs
dotnet/tests/AnthropicChatCompletion.IntegrationTests/AnthropicChatCompletionRunStreamingTests.cs	Integration tests for streaming agent runs
dotnet/tests/AnthropicChatCompletion.IntegrationTests/AnthropicChatCompletionChatClientAgentRunTests.cs	Integration tests for ChatClientAgent runs
dotnet/tests/AnthropicChatCompletion.IntegrationTests/AnthropicChatCompletionChatClientAgentRunStreamingTests.cs	Integration tests for streaming ChatClientAgent runs
dotnet/src/Shared/IntegrationTests/AnthropicConfiguration.cs	Configuration class for Anthropic integration tests
dotnet/samples/GettingStarted/README.md	Updated to reference new Anthropic samples
dotnet/samples/GettingStarted/AgentWithAnthropic/README.md	Documentation for Anthropic agent samples
dotnet/samples/GettingStarted/AgentWithAnthropic/Agent_Anthropic_Step01_Running/Program.cs	Sample demonstrating basic Anthropic agent usage
dotnet/samples/GettingStarted/AgentWithAnthropic/Agent_Anthropic_Step02_Reasoning/Program.cs	Sample demonstrating extended thinking/reasoning capabilities
dotnet/samples/GettingStarted/AgentWithAnthropic/Agent_Anthropic_Step03_UsingFunctionTools/Program.cs	Sample demonstrating function tool integration
dotnet/samples/GettingStarted/AgentProviders/README.md	Updated to reference new Anthropic provider sample
dotnet/samples/GettingStarted/AgentProviders/Agent_With_Anthropic/Program.cs	Sample showing different deployment scenarios (Public API, Azure Foundry)
dotnet/samples/GettingStarted/AgentProviders/Agent_With_OpenAIChatCompletion/Program.cs	Unrelated code accidentally added
dotnet/nuget.config	Added local package source (developer-specific path)
dotnet/Directory.Packages.props	Added Anthropic package references
dotnet/agent-framework-dotnet.slnx	Added new projects to solution