  C++ Modules come in C++20 to fix the long-standing build scalability problems
in the language. They provide an io-efficient, on-disk representation capable
to reduce build times and peak memory usage. ROOT employs the C++ modules
technology further in the ROOT dictionary system to improve its performance and
reduce the memory footprint.
  ROOT with C++ Modules was released as a technology preview in fall 2018,
after intensive development during the last few years. The current state is
ready for production, however, there is still room for performance
optimizations. In this talk, we show the roadmap for making the technology
default in ROOT. We demonstrate a global module indexing optimization which
allows reducing the memory footprint dramatically for many workflows. We will
report user feedback on the migration to ROOT with C++ Modules.
