An above-threshold analysis of 8–10-μm-core antiresonant reflecting optical waveguide (ARROW) lasers is performed, including the carrier-induced index depression, carrier diffusion, and gain spatial hole burning (GSHB). The study is done as a function of the (transverse) optical-mode confinement factor Γ and the core width. Just as for index-guided devices, it is found that ARROW devices (i.e., index-antiguided devices) are much less immune to multimoding via GSHB the smaller the value of Γ. For the case Γ=3%, the high-order mode of most concern reaches the threshold much earlier than for the case Γ=1%, due both to gain-profile distortion as well as to distortion of the effective-index profile (in the device core) with increasing drive level. Devices of 8.5-μm-wide cores and Γ=1%, are found to stay single-mode to at least 40× threshold, which in turn allows the projection of stable, single-mode operation to 1.2 W output power. In contrast, 10-μm-core devices become multimode at around 10× threshold. Preliminary experimental results from 10-μm-wide core ARROW lasers, with Γ=1.5%, are stable, single-mode operation to 300 mW at 10× threshold, in good agreement with the presented study. © 2002 American Institute of Physics.