Mods sit in panels, tool calls and commands.
So the thing you used to write as an instruction and hope it followed can now be code it cannot argue with.
That is a real change. Configuring Claude Code used to mean a settings file with static values in it.
Now it can be logic that runs at the moment a tool is called.
And it answers a question people kept asking. Nobody is loyal to one agent now.
They want Claude Code for one job and something cheaper for another, in the same session.