The Teams client, starting with Office 365 ProPlus build 1902, will be deployed automatically as part of the Office 365 ProPlus update cadence.

If your organization isn't ready to deploy Microsoft Teams and you're using Office 365 ProPlus, you can use the Office Deployment Tool to prevent Teams from being installed or Group Policy to prevent Teams from being launched automatically.

The XML configuration file generated by the Office Deployment Tool should contain an ExcludeApp node that indicates Teams won't be installed:

<Configuration>
 <Add Version="MatchInstalled">
 <Product ID="O365ProPlusRetail">
 <Language ID="MatchInstalled" TargetProduct="All" />
 <ExcludeApp ID="Teams" />
 </Product>
 </Add>
 <Display Level="None" />
</Configuration>

If you want to deploy Teams as part of Office 365 ProPlus but prevent the Teams desktop client from launching automatically the first time a user logs on, you can use Group Policy to modify that behavior. Using the Office 365 ProPlus version 1905 or later and 4882.1000 or later of the Office Administrative Templates, you can configure the following policy option:

User ConfigurationPoliciesAdministrative TemplatesMicrosoft TeamsPrevent Microsoft Teams from starting automatically after installation

The caveat for this Group Policy setting is that it must be configured before the Office 365 ProPlus image with Teams is installed. Configuring it after the fact will have no impact on Teams.