Example of splitting a main routes file into smaller route files

routes.rb

Rails.application.routes.draw do
  # ...
  draw :v1
  draw :v2
  # ...
end

routes_drawing.rb

class ActionDispatch::Routing::Mapper
  def draw(routes_name)
    instance_eval(File.read(Rails.root.join("config/routes/#{routes_name}.rb")))
  end
end

v1.rb

namespace :v1 do
  namespace :auth do
    # ...
  end
  # ...
  resources :topics
  # ...
end

v2.rb

namespace :v2 do
  namespace :auth do
    # ...
  end
  # ...
  resources :topics
  # ...
end