def matches?(req)
@default || req.headers['Accept'].include?("application/vnd.example.v#{@version}")
end
end

Basic versioning

namespace :v1 do
resources :users, :courses, :assignments
end

Nested structure for API-only apps

namespace :api do
namespace :v1 do
resources :posts, :comments
end
namespace :v2 do
resources :posts, :comments
end
end
end

namespace :v1 do
concerns :api
end

namespace :v2 do
concerns :api
end
end

Updated: app/controllers/v1/courses_controller.rb

class V1::CoursesController < ApplicationController

controller logic

end

For nested APIs: app/controllers/api/v1/users_controller.rb

module Api
module V1
class UsersController < ApplicationController
# controller logic
end
end
end

namespace :v1 do
concerns :api
end

namespace :v2 do
concerns :api
end

Default unversioned requests to v1

scope module: 'v1' do
concerns :api
end
end

private

def add_deprecation_headers
response.headers['Deprecation'] = 'true'
response.headers['Sunset'] = 'Wed, 31 Dec 2025 23:59:59 GMT'
response.headers['X-DEPRECATION-WARN'] = 'API v1 will be removed on 31 December 2025. Please migrate to v2.'
end
end