Concern module not available in model despite being included (NoMethodError)

I'm migrating my app from solr to Elasticsearch for document searching. The recommended pattern for deploying Elasticsearch is to include the Elasticsearch functionality (ie Elasticsearch::Model and Elasticsearch::Model::Indexing) in a Rails concern and then include this module in your model. I've implemented this as such. (Some methods temporarily commented out as I'm working through this.)

#app/models/concerns/elasticsearch_user.rb
require 'active_support/concern'

module ElasticsearchUser

extend ActiveSupport::Concern

included do
  require 'elasticsearch/model'
  include Elasticsearch::Model
  include Elasticsearch::Model::Indexing

  #mapping do
  #  #to-do
  #end

  #def self.search(query)
  #  _elasticsearch_.search(
  #    {
  #        query: {
  #         multi_match: {
  #             query: query,
  #             fields: ['username^2', 'email', 'full_name']
  #         }
  #        }
  #    }
  #  )
  #end

  end
end


#User.rb
...
# Elasticsearch configuration
include ElasticsearchUser
# index_name "users" <-- This value is inferred automatically by the model name
settings index: { number_of_shards: 1 } do
  mappings dynamic: 'false' do
    indexes :username
    indexes :email
    indexes :full_name
  end
end
...
def as_indexed_json(options={})
  self.as_json(only: [:username, :email, :full_name],
               methods: [:full_name]
  )
end

I can call Model.import and Model.search with no problems. Calling things like Model._elasticsearch_.create_index! (with and without the _elasticsearch_ namespace) throw a NoMethodError. I've tried including Elasticsearch::Model directly in my model definition with no success. I've also tried requiring `active_support/concern' at the top of my model - no luck there either. It seems obvious that the module/concern is not being included in my model but I can't figure out why.