Built-in agent pools are managed by Microsoft and are made available to you as part of the product. There are different agent pools available, depending on your needs. Pools run different versions of Windows and Visual Studio, and there are also pools available that run Linux (Ubuntu) and macOS.

The disadvantage of these managed pools is that you cannot install extra software on the machines or containers that host the agents if you need to. This means that in these cases, you have to create your own private agent pools.