It's real Chromium, not emulating a Chromium browser. "Old" Headless was merely pretending to be a Chromium browser, the "New" Headless is a Chromium browser. "Old" Headless requires a parallel/duplicate implementation of features, which leads to subtle behavior differences or infeasability to support certain features e.g. extensions proper.
Does this mean we might see proper extension support in "New" Headless?
wow, i had no idea the old headless was a reimplementation. congrats on landing the new one