7:55pm: Manager Bob Melvin told reporters (including Joe Stiglich of The Bay Area News Group and MLB.com's Jane Lee) that the plan was for Barton to be the first baseman all along. Kila Ka'aihue played better, and he expects Allen to get claimed off waivers (Twitter links).
Allen, 26, was acquired from the Diamondbacks at last year's trade deadline along with reliever Jordan Norberto for right-hander Brad Ziegler. With a glut at first base, the A's were said to be shopping Allen over the winter.
The first baseman/leftfielder has a .286/.401/.555 slash line across parts of three Triple-A seasons but yet to put it all together in the majors. In 109 big league games for the D'Backs and A's, Allen has hit .205/.291/.375 with eleven homers.