Build 2025: The Copilot Stack Deep Dive

The Copilot Stack represents Microsoft’s comprehensive approach to AI-assisted applications. Here’s what’s new.

Copilot Stack Architecture

Layer 1: Foundation Models

• Access to GPT-5, Claude 4, Gemini 2
• Microsoft’s own models (Phi-4, MAI-1)
• Automatic model routing and fallback

Layer 2: AI Orchestration

• Semantic Kernel 2.0 release
• Built-in memory and planning
• Cross-service orchestration

Layer 3: Copilot Services

• Grounding with enterprise data
• Safety and compliance filters
• Multi-turn conversation management

Layer 4: User Experiences

• Copilot in Microsoft 365
• Custom Copilots in Copilot Studio
• Embedded Copilot components

Building Custom Copilots

// Copilot Studio API for custom copilots
using Microsoft.Copilot.Studio;

var copilot = new CopilotBuilder()
    .WithName("SalesAssistant")
    .WithDescription("Helps sales team with customer insights")
    .WithModel("gpt-4o")
    .WithGrounding(new GroundingConfig
    {
        DataSources = new[]
        {
            new SharePointDataSource("https://company.sharepoint.com/sales"),
            new DynamicsDataSource("https://company.crm.dynamics.com")
        },
        SearchType = SearchType.Hybrid
    })
    .WithTopics(new[]
    {
        new Topic("CustomerLookup", "Find customer information"),
        new Topic("SalesForecast", "Get sales predictions"),
        new Topic("CompetitorAnalysis", "Analyze competitors")
    })
    .WithSafetyFilters(SafetyLevel.Enterprise)
    .Build();

// Deploy copilot
var deployment = await copilot.DeployAsync(new DeploymentConfig
{
    Channel = Channel.Teams,
    Users = UserGroup.SalesTeam,
    Analytics = true
});

Copilot Extensions Framework

// Building a Copilot extension
import { CopilotExtension, Message, Response } from '@microsoft/copilot-sdk';

class InventoryExtension extends CopilotExtension {
    name = "Inventory Lookup";
    description = "Check product inventory levels";

    async handleMessage(message: Message): Promise<Response> {
        const product = this.extractProduct(message.text);
        const inventory = await this.inventoryService.check(product);

        return {
            text: `Current inventory for ${product}: ${inventory.quantity} units`,
            adaptiveCard: this.buildInventoryCard(inventory),
            citations: [{ source: "Inventory System", url: "..." }]
        };
    }
}

The Copilot Stack makes it straightforward to build AI-powered applications across the Microsoft ecosystem.