$ sbt sbtVersion
This prints the sbt version used in your current project, or if it is a multi-module project for each module.
$ sbt 'inspect sbtVersion'
[info] Set current project to jacek (in build file:/Users/jacek/)
[info] Setting: java.lang.String = 0.13.1
[info] Description:
[info] Provides the version of sbt. This setting should be not be modified.
[info] Provided by:
[info] */*:sbtVersion
[info] Defined at:
[info] (sbt.Defaults) Defaults.scala:68
[info] Delegates:
[info] *:sbtVersion
[info] {.}/*:sbtVersion
[info] */*:sbtVersion
[info] Related:
[info] */*:sbtVersion