Rails core team decided to not include Rails.queue in the 4.0 release. @jeremy has a nice writeup for the reasons:

• Resque’s interface is currently easier to use than Rails.queue’s
• Marshalling has some issues
• Rails.queue is abstracting at the wrong level (equivalent to imaginary Rails.database)
• Not efficient when working with Russian doll caching
• There might be a better way to avoid marshalling and Job classes alltogether by processing certain jobs after the response has been sent to client. However this requires work on the Rack integration.

Link: Move background jobs to the ‘jobs’ branch until fully baked. Not shippin… · f9da785 · rails/rails via github.com