Antiferromagnets are emerging as a transformative platform for next-generation spintronics and information storage technologies, promising improved speed and energy efficiency. However, unlike in ferromagnets---where magnetic domain stability is governed by long-range magnetostatic fields---the physical principles defining the minimum writable domain size in antiferromagnets remain poorly understood. Here we identify the Larkin length---the scale at which disorder-induced pinning of domain walls and elastic restoring forces balance---as a key parameter governing the ultimate resolution for stable antiferromagnetic domain writing. We observe that the Larkin length decreases sharply near the Neel transition, enabling deterministic electrical writing of micrometer-scale domains in the archetypal antiferromagnet Cr2O3. Exploiting this mechanism, we demonstrate Heat-Assisted Antiferromagnetic Recording using picosecond laser heating, as a direct analog of Heat-Assisted Magnetic Recording on ferromagnetic media. These findings establish a framework for understanding domain stability in antiferromagnets and provide practical pathways for deterministic electrical and optical domain writing towards extreme-density ferroic devices.