Sitecore Installation Framework 2.1.0 has been released. This version is required if you want to deploy Sitecore 9.1 Update 1.
You can obtain this version at https://sitecore.myget.org/feed/sc-powershell/package/nuget/SitecoreInstallFramework/2.1.0
If you are using PowerShell to get the package you would use a call akin to the following. Note, its a good practice to still download Sitecore Fundamentals for standard operations:
Register-PSRepository -Name sc-powershell -SourceLocation https://sitecore.myget.org/F/sc-powershell/api/v2 # Install Sitecore Fundamentals (Required for Standard Operations) Install-Module -Name "SitecoreFundamentals" -RequiredVersion "1.1.0" -Repository "sc-powershell" -Force # Install Sitecore Install Framework Install-Module -Name "SitecoreInstallFramework" -RequiredVersion "2.1.0" -Repository "sc-powershell" -Force