Broadband optical interfaces for IR sensing must retain stable spectral coupling after thermal exposure. In this study, p-type black GaAs nanotip arrays (GaAsNTs) fabricated by self-masked dry etching were evaluated at the materials level as front optical coupling interfaces for IR sensing. Hemispherical absorptance over 250–2400 nm was measured in the as-prepared state and after thermal exposure at 200, 500, and 700 °C for 30 min. All post-exposure spectra were acquired at room temperature after cooling, and NIR absorptance retention was used to quantify optical durability. The as-prepared GaAsNTs exhibited near unity broadband absorptance. After exposure at 200 and 500 °C, the response remained largely unchanged, with 98.5% NIR absorptance retention after 500 °C exposure. In contrast, exposure at 700 °C reduced retention to 75.8% and produced the cracking, nanotip collapse, and partial removal of the nanostructured layer, suggesting a structural contribution to optical degradation. To the best of our knowledge, this is the first systematic evaluation of broadband hemispherical absorptance retained by black GaAs nanotip surfaces after thermal exposure. These results provide an application-oriented materials assessment for IR sensor interface design under thermal exposure constraints. They also distinguish post-exposure durability from continuous high-temperature operation.