This technical report documents the PTR-500 validation protocol conducted under SIGMA Runtime v0.5.x — a persistent cognitive control architecture for multi-model AI systems. The evaluation covers 500 cognitive cycles across two large language models (Google Gemini-3-Flash-Preview and OpenAI GPT-5.2), executed under the PTR-500 test protocol within the SIGMA Runtime v0.5.x architecture (SRIP-09 Long-Term Memory, SRIP-09c Density Nucleus and SRIP-10-AEP enabled). Results confirm zero semantic drift, stable identity persistence, and self-healing behavior over extended reasoning sequences. The report includes forensic metrics, drift heatmaps, coherence trajectories, and final architectural theorems demonstrating model-agnostic cognitive stability. Produced by the Sigma Stratum Research Group, January 2026.