Paths, Not Parrots: When RL Makes LLMs Plan—and When It Doesn’t
A workflow agent usually looks clever right up to the moment one service is down, one permission changes, or one customer case arrives with the wrong sort of mess attached. Then the question becomes painfully simple: did the model learn a plan, or did it learn the usual route? That distinction is the centre of Benefits and Pitfalls of Reinforcement Learning for Language Model Planning: A Theoretical Perspective, an ICLR 2026 paper by Siwei Wang, Yifei Shen, Haoran Sun, Shi Feng, Shang-Hua Teng, Li Dong, Yaru Hao, and Wei Chen.1 The paper is not another victory lap for reinforcement learning. It is more useful than that. It asks what, mechanically, changes when a language model is trained for planning with reinforcement learning rather than supervised fine-tuning. ...