A Tier-1 environment is a single-box environment and is typically used as a development and build environment. The architecture of the Tier-1 environment is different from a production environment. In this environment, the SQL Server database is used, and all components such as AOS, batch, database, management reporter, and many others are installed on the same server.
The Business Application October 2019 release plan includes features to enhance the development tooling to enable development using local computers, instead of a pre-configured Tier -1 environment. It is also planned to replace the build process as a standard Microsoft DevOps process. These features, when available, will eliminate the need for the Tier-1 environment for development and build purposes.