Preprint
Newly Important Is Not Newly Built: What Reasoning Post-Training Adds Inside a Language Model, Why the Evidence Separates Representation From Wiring From Deployment, and the Cross-Model Tests That Would Show an Attention Head Is New
(c) 2026 Pranay Mahendrakar. Licensed under CC BY 4.0. Life of Research Reasoning models are built by post-training a pretrained model with supervised fine-tuning on teacher traces, with reinforcement learning against a verifier, or with both, and a running dispute asks whether this builds new…