  We characterize the fundamental limits of transmission of information over a
Gaussian multiple access channel (MAC) with the use of variable-length feedback
codes and under a non-vanishing error probability formalism. We develop new
achievability and converse techniques to handle the continuous nature of the
channel and the presence of expected power constraints. We establish the
$\varepsilon$-capacity regions and bounds on the second-order asymptotics of
the Gaussian MAC with variable-length feedback with termination (VLFT) codes
and stop-feedback codes. We show that the former outperforms the latter
significantly. Due to the multi-terminal nature of the channel model, we
leverage tools from renewal theory developed by Lai and Siegmund to bound the
asymptotic behavior of the maximum of a finite number of stopping times.
