In the appendix to chapter I of Pursuing stacks, Grothendieck writes:

A large part of the letter outlines (very sketchily) some main points of a duality program (including a cohomological formulation of “geometric” local and global class field theory), which emerged by the end of the fifties and appears here for the first time in print.

For example App 12 is entitled "Global “geometric” class field theory as a cohomological duality formula. Serre duality and the “Lang trick”." and 13 "Case of local “geometric” class field theory."

Hope this helps!

In the appendix to chapter I of Pursuing stacks, Grothendieck writes:

A large part of the letter outlines (very sketchily) some main points of a duality program (including a cohomological formulation of “geometric” local and global class field theory), which emerged by the end of the fifties and appears here for the first time in print.

For example App 12 is entitled "Global “geometric” class field theory as a cohomological duality formula. Serre duality and the “Lang trick”." and 13 "Case of local “geometric” class field theory."

Hope this helps!