The notion of a probationary period is largely mythological for places where employment is at-will (which is most jobs in technology in the U.S.). Since at-will employment means you can mostly be terminated for any reason at any time, every day you go to work is really part of your probationary period. There's no concept of a "long-term commitment" and your status as an employee doesn't materially change after whatever "probationary period" the employer might extend to you.