Claude Opus 4.5 Arrives on Azure: What .NET Developers Need to Know

TL;DR Anthropic released Claude Opus 4.5, achieving 80.9% accuracy on SWE-bench Verified, outperforming OpenAI’s GPT-5.1-Codex-Max (77.9%), Sonnet 4.5 (77.2%), and Google’s Gemini 3 Pro (76.2%) . Pricing dropped dramatically to $5 per million input tokens and $25 per million output tokens—down from $15 and $75 for Claude Opus 4.1 . Anthropic is scaling Claude on Microsoft Azure, and Azure customers can now access Claude Sonnet 4.5, Claude Opus 4.1, and Claude Haiku 4.5 through Microsoft Foundry .

The Story: Frontier Models Come to Azure

As of November 26, 2025, the AI landscape for cloud developers just shifted. Microsoft and Anthropic are expanding their existing partnership to provide broader access to Claude for businesses, with customers of Microsoft Foundry able to access Anthropic’s frontier Claude models . For .NET teams building on Azure, this is a watershed moment—you no longer have to choose between OpenAI and open-source models.

What This Means for Cost and Performance

The pricing story is the most immediately actionable. Claude Opus 4.5 pricing at $5/$25 per million tokens represents a dramatic reduction from the previous $15/$75 rates, making frontier AI capabilities accessible to a broader swath of developers and enterprises while putting pressure on competitors to match both performance and pricing .

For a typical .NET application processing 1 billion tokens monthly:

Claude Opus 4.5: ~$30,000/month (input + output blended)
Previous Opus 4.1: ~$90,000/month
Savings: 67% cost reduction

Integration with .NET and Azure

AI-focused capabilities expand through the Microsoft Agent Framework, Microsoft.Extensions.AI, and first-class Model Context Protocol (MCP) support, aiming to standardize patterns for building agentic workflows, integrating external tools, enabling telemetry, and working across multiple AI providers .

Here’s how to get started with Claude Opus 4.5 in .NET on Azure:

using Azure.AI.Inference;
using System.ClientModel;

// Initialize the Azure OpenAI client pointing to Claude
var client = new ChatCompletionsClient(
    endpoint: new Uri("https://<your-resource>.openai.azure.com/"),
    keyCredential: new ApiKeyCredential(Environment.GetEnvironmentVariable("AZURE_OPENAI_API_KEY"))
);

// Call Claude Opus 4.5 via Azure
var response = await client.CompleteAsync(
    new ChatCompletionOptions
    {
        Model = "claude-opus-4-5",
        Messages =
        {
            new ChatCompletionMessage(ChatRole.User, "Analyze this .NET codebase for performance bottlenecks")
        }
    }
);

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

Why This Matters Right Now

Anthropic’s internal testing revealed Claude Opus 4.5 achieved a qualitative leap in reasoning capabilities, achieving 80.9% accuracy on SWE-bench Verified, a benchmark measuring real-world software engineering tasks . For .NET developers, this translates to better code generation, architectural suggestions, and debugging assistance—especially for complex, multi-step refactoring tasks. Claude models are engineered for the realities of enterprise development, from tight integration with productivity tools to deep, multi-document research and agentic software development across large repositories, built on Constitutional AI for safety and deployable through Foundry with governance, observability, and rapid integration, enabling secure use cases like customer support agents, coding agents, and research copilots .

Practical Next Steps

Update your Azure AI Foundry projects to include Claude Opus 4.5 as a deployment option alongside GPT models.
Leverage Microsoft.Extensions.AI abstractions to swap models without rewriting code—this is the abstraction layer Microsoft designed for exactly this scenario.
Monitor token usage carefully; the cost savings are real, but consumption patterns may shift as teams discover new use cases. 4. Microsoft has committed to continuing access for Claude across Microsoft’s Copilot family, including GitHub Copilot, Microsoft 365 Copilot, and Copilot Studio —so your GitHub Copilot experience will improve as well.

The Broader Context

Anthropic has committed to purchase $30 billion of Azure compute capacity and to contract additional compute capacity up to one gigawatt . This isn’t a marketing partnership—it’s a deep infrastructure bet that signals Azure’s commitment to remaining a genuine multi-model platform, not just an OpenAI reseller.