Is the content different on the HiSET and GED?
The subjects overlap heavily: algebra-heavy math, reading informational and literary texts, grammar, life and physical science, and U.S. history and civics. The bigger differences are in format and the essays.
The HiSET is almost entirely multiple choice and splits language arts into separate Reading and Writing subtests, with an essay in which you take and support a position. The GED combines reading and writing in one long Language Arts subject, uses drag-and-drop, drop-down and fill-in items as well as multiple choice, and its essay asks you to judge which of two arguments is better supported rather than give your own view.
GED math gives you an on-screen calculator and a formula sheet for most of the test; the HiSET is calculator-neutral and leaves some formulas, such as the Pythagorean theorem, off its sheet. See the HiSET math practice test and the GED math practice test.