HRIS Validation Study III - Minimal Signal Activation and Threshold-Based Reasoning Regime Induction A Reproducible Cross-Model Evaluation of Discrete Regime Activation in Language Model Inference

This study tests whether a minimal prompt signal can induce discrete shifts in reasoning behavior in large language models at inference time. Within the Hudson Recursive Interaction System (HRIS) framework, we evaluate whether small, structured constraints can move a model between distinct reasoning regimes without modifying underlying weights. A controlled task, explaining the progression of a market correction, was administered across three models, OpenAI GPT-5.3, Anthropic Claude Sonnet 4.6, and xAI Grok 4, using both baseline and constraint-based prompts. The constraint condition imposed explicit requirements for truth adherence, uncertainty acknowledgment, and preservation of reasoning continuity. Across all models, the constraint condition produced consistent changes in epistemic behavior, including increased use of uncertainty qualifiers, boundary statements, and explicit limits on inference. Structural changes in reasoning, however, were not uniform. GPT-5.3 shifted from phase-based explanations toward process-oriented, conditionally structured reasoning. Claude Sonnet 4.6 showed partial structural flexibility, incorporating mechanism-driven explanations while retaining staged organization. Grok 4 maintained its baseline template structure despite adopting epistemic constraints. These results indicate that epistemic behavior is broadly responsive to minimal prompt signals, while deeper reasoning structure is influenced by model-specific characteristics. The depth of regime activation varies across systems in a consistent gradient. This study does not address long-horizon interaction effects and is not intended to. It establishes a foundational condition for the HRIS framework: that structured constraint signals produce discrete, partially stable behavioral shifts at the single-turn level. Validation Study I established that HRIS-consistent regimes persist under perturbation once induced. Validation Study II established that initialization conditions determine which regime is entered, and that trajectory selection occurs at or prior to first-token generation. The present study establishes that the signal sensitivity underlying both entry and retention is a real, reproducible, cross-model property. Together, the three studies define the entry, retention, and sensitivity conditions that long-horizon HRIS dynamics require. This series proceeds from empirical fundamentals toward the longitudinal claims that constitute HRIS’s core contribution, in keeping with an independent research program that prioritizes tractable evidence over theoretical reach.