# Reasoning Architecture: <think> Token + Segregated vs Interleaved CoT Decision Matrix

> Source: https://sukruyusufkaya.com/en/learn/fine-tuning-cookbook/ftc-reasoning-architecture-think-token
> Updated: 2026-05-14T14:42:58.788Z
> Category: Fine-Tuning Cookbook (Model-by-Model)
> Module: Part XII — Reasoning Model FT (R1-style)
**TLDR:** Reasoning models split: (1) **Segregated** — reasoning in <think>...</think> block (DeepSeek-R1, o-series), then final answer; (2) **Interleaved** — reasoning + answer mixed (classic CoT, GPT-4-1106). Each's advantages, FT challenges, user UX. Token budget management.