# Microsoft Teams development SDK Guidance - Fall 2025

Microsoft's Teams development tools have evolved from Teams JS and Teams FX to multiple competing SDKs. Here's what you need to know about which to use.

by Andrew Connell

Last updated October 14, 2025

## TL;DR
- TeamsFX is being replaced by the Teams AI v2, which handles tabs, bots, message extensions, AI-powered agents, and other Microsoft Teams solutions
- The Bot Framework is being replaced by the Microsoft 365 Agents SDK that is designed for multi-channel agents beyond Teams using Azure AI Bot Service
- The current guidance on when to use Teams AI v2 versus M365 Agents SDK, and the developer tooling, is confusing and not helpful in guiding developers down the right path
- Azure AI Foundry Agent SDK adds another option to the mix, making the decision matrix even more complex

## The original Teams developer experience
Initially, Microsoft Teams development was straightforward. We had the Teams JS library, a client-side JavaScript library that tabs used to communicate with the Teams client. Simple enough.

Then came [TeamsFX](https://www.npmjs.com/package/@microsoft/teamsfx), a collection of packages ( _some Node.js, some .NET_) that handled various server-side tasks. We used TeamsFX for things like Azure Function extensions that automatically handled authentication, ensuring calls from Teams apps were properly authenticated. It also included a React package ( **@microsoft/teamsfx-react**) that included some useful React hooks for working with Microsoft Graph and other SDK-related functionality.

For chat bots and message extensions, we relied on the Bot Framework v4. This became the infrastructure for message extensions and bot interactions.

## Enter the Teams AI Library v1
When large language models became a big deal, Microsoft released the Teams AI Library v1 (released November 2023). This library was built on top of the Bot Framework and was designed to leverage language models (LLMs) to deduce user intent and generate more intelligent responses. It represented a change in Microsoft’s push toward AI-powered conversational experiences in Teams as previously, any natural language processing was handled with LUIS.

## The current landscape: multiple competing SDKs
Microsoft appears to have launched what looks like simultaneous projects: the Microsoft 365 Agents SDK and the Teams AI v2.

### Teams AI v2: the new successor SDK to the TeamsFX
The Teams AI v2, released in September 2025, is the successor to what we used to call TeamsFX. It’s an isomorphic JavaScript library that also comes in .NET and Python flavors. This SDK handles everything we used to do with TeamsFX - including tabs, bots, message extensions, and dialogs - and it includes the AI capabilities from the Teams AI Library v1.

The SDK also includes a concept of plugins. For example, there’s a plugin for an Model Context Protocol (MCP) client, MCP server, Agent-2-Agent (A2A) support and other extensibility options.

You’ll find this SDK in a GitHub repo [`https://www.github.com/microsoft/teams-ai`](https://www.github.com/microsoft/teams-ai) and referred to as Teams AI V2.

### Microsoft 365 Agents SDK: the multi-channel option
The Microsoft 365 Agents SDK, announced at Ignite in November 2024 and released at Build in May 2025, also exists as JavaScript, Python, and .NET SDKs. The current guidance suggests you should use the M365 Agents SDK when you want to build a Custom Engine Agent (CEA) that works in more than just Teams.

But here’s the problem: if that’s the case, shouldn’t that capability be something the Teams AI v2 handles?

### Adding to the confusion: Azure AI Foundry Agent SDK
As if two competing SDKs weren’t enough, there’s also the [Azure AI Foundry Agent SDK](https://learn.microsoft.com/azure/ai-foundry/how-to/develop/sdk-overview?WT.mc_id=M365-MVP-21083). Now the question becomes: when would I use that compared to the other two?

## What this means for developers
If you’re building a Teams-only solution, one with tabs, bots, message extensions, or AI-powered chatbots that live exclusively in Teams, then **the Teams AI v2 is your best bet.**

If you’re building an agent that needs to work across multiple channels beyond Teams, you’ll likely want to use the Microsoft 365 Agents SDK.

## What should you use?
| If you need… | Use this SDK |
| --- | --- |
| Teams-only: tabs, bots, msg extensions | Teams AI [SDK] v2 |
| Multi-channel agents (Slack, web, etc.) | Microsoft 365 Agents SDK |
| ??? (unclear guidance from Microsoft) | Azure AI Foundry Agent SDK |

## Looking ahead
If you’re starting a new Teams project today, I recommend starting with the Teams AI v2 unless you have a specific requirement for multi-channel agent deployment and not creating tabs, meeting extensions, or message extensions.

**What’s been your experience navigating Microsoft’s Teams SDK options?**