Each ebuild in the Portage tree used to come with its own digest
file. When you emerged a package, this digest was used to verify that
you had the same files the developer did.

A few days ago, all digest files were erased from the Portage tree in
CVS as part of the final work to implement GLEP 44.
This migrates that information to a single Manifest file
per package instead of one digest for every ebuild of that
package. Portage hasn't been downloading these digest files for about a
year, so this won't reduce the size of your tree again (it shrunk by
~200M at the time).

If you're still stuck on a Portage version in the 2.0.x series, follow
the guide below on how to temporarily get Manifest1 files so you can
update your Portage to the 2.1.x series.

References:

• 
  Migrating back to Manifest1 for portage-2.0.x systems
• 
  Understanding digest and manifest files
• GLEP 44: Manifest2 format
• 
  [gentoo-dev] RFC: removal of digest files from the tree by Zac Medico
• 
  [gentoo-dev] Redux: removal of digest files from the tree by Robin H. Johnson

Discuss
this!

Łukasz Damentko and Joshua Nichols contributed the draft for this
announcement.

Correction: This was just the final step in a long-term migration
that actually reduced the size of your Portage tree last
February. Thanks to Daniel Drake, Petteri Räty and Jan Kundrat for
pointing this out.