Claude Opus 4.5 Hits Azure AI Foundry: What .NET Developers Need to Know

TL;DR: Azure is now the only cloud providing access to both Claude and GPT frontier models to customers on one platform . Opus 4.5 delivers frontier performance and sets a new standard for a variety of use cases at one third the price of previous Opus-class models . If you’re building agents or reasoning-heavy workloads on Azure, you now have a compelling alternative to OpenAI models—and you can route between them intelligently.

The Setup: Multi-Model Parity on Azure

Until recently, Azure developers had a single frontier model path: OpenAI. That’s no longer true. Anthropic is scaling its rapidly-growing Claude AI model on Microsoft Azure, powered by NVIDIA, which will broaden access to Claude and provide Azure enterprise customers with expanded model choice and new capabilities . This isn’t just marketing—it’s a real architectural shift that changes how you design AI applications. Customers of Microsoft Foundry will be able to access Anthropic’s frontier Claude models including Claude Sonnet 4.5, Claude Opus 4.1, and Claude Haiku 4.5 . For .NET developers, this means you can now deploy Claude through the same Azure infrastructure you already use for GPT models.

Why This Matters for Your Code

Cost optimization: Opus 4.5 delivers frontier performance at one third the price of previous Opus-class models . If you’re running high-volume agentic workloads, routing simpler tasks to Haiku and complex reasoning to Opus can significantly reduce your bill.

Agent reasoning: Inside Foundry Agent Service, Claude models serve as the reasoning core behind intelligent, goal-driven agents. Developers can plan multi-step workflows by leveraging Claude in Foundry Agent Service to orchestrate complex, multi-stage tasks with structured reasoning and long-context understanding .

Hands-on integration: You can now use Claude directly in your .NET applications via the Anthropic SDK or through Azure’s OpenAI Responses API. Here’s a quick Python example (C# SDK support is also available):

from anthropic import AnthropicFoundry
from azure.identity import DefaultAzureCredential, get_bearer_token_provider

# Authenticate with Azure credentials
tokenProvider = get_bearer_token_provider(
    DefaultAzureCredential(), 
    "https://cognitiveservices.azure.com/.default"
)

# Create client pointing to your Azure Foundry deployment
client = AnthropicFoundry(
    azure_ad_token_provider=tokenProvider,
    base_url="https://<your-resource>.services.ai.azure.com/anthropic"
)

# Call Claude Opus 4.5
message = client.messages.create(
    model="claude-opus-4-5",
    messages=[
        {"role": "user", "content": "Analyze this customer support ticket and suggest a resolution."}
    ],
    max_tokens=1024
)

Model Router: Automatic Intelligence Routing

One of the smartest moves here is Model Router, a Foundry model that intelligently routes each prompt to the best underlying model based on query complexity, cost, and performance. Version 2025-11-18 supports Claude Haiku 4.5, Sonnet 4.5, and Opus 4.1 alongside GPT, DeepSeek, Llama, and Grok models .

This means you can deploy a single endpoint and let the router decide: simple classification queries go to Haiku (fast, cheap), multi-step planning goes to Opus. You get the best of both worlds without managing multiple deployments.

Enterprise Security: MCP + Azure API Management

If you’re building agents that need secure access to enterprise data, a production-ready approach to building secure Claude integrations uses Azure API Management (APIM) as your OAuth 2.0 gateway, powered by Microsoft Entra ID . This means Claude agents can safely call your internal APIs without exposing credentials.

The Gotchas

- Claude models in Foundry are available for global standard deployment (not provisioned throughput yet, though that may change).

You’ll need to authenticate with either Entra ID or API keys; make sure your deployment is in a region that supports Foundry.

Opus 4.5 paired with new developer capabilities includes an Effort Parameter (Beta) to control how much computational effort Claude allocates across thinking, tool calls, and responses, and Compaction Control to handle long-running agentic tasks more effectively —these are beta features, so expect iteration.

Next Steps

Deploy Claude in Foundry: Follow the Microsoft Learn guide to add Claude models to your Foundry project.
Test with Model Router: Set up the router to see cost/latency tradeoffs across models.
Integrate with your agents: If you’re using Foundry Agent Service or Microsoft Agent Framework, Claude is now a first-class option alongside GPT.

The agentic era is here, and now you have real choice. Use it.