Decision Transformer: Reinforcement Learning via Sequence Modeling
Lili ChenKevin LuAravind RajeswaranKimin LeeAditya GroverMichael LaskinPieter AbbeelAravind SrinivasIgor Mordatch
Introduces Decision Transformer, a sequence modeling approach to offline reinforcement learning that generates actions by conditioning an autoregressive Transformer on desired returns, matching or surpassing standard baselines without using dynamic programming or policy gradients.
The article addresses challenges in offline reinforcement learning, where agents must learn effective policies from fixed datasets of past experiences without further interaction. Traditional methods relying on temporal difference learning often suffer from error propagation, value overestimation, and difficulties with sparse or delayed rewards, limiting their reliability in complex sequential decision tasks.
The article set out to evaluate whether framing reinforcement learning as a conditional sequence modeling problem, using a Transformer architecture, could produce policies that match or exceed dedicated offline RL algorithms without relying on value functions or policy gradients.
The approach involved training a causally masked GPT-style model on trajectories represented as sequences of desired returns-to-go, states, and actions drawn from offline datasets. Experiments covered discrete control in four Atari games using 1% of DQN replay data, continuous control in OpenAI Gym locomotion and reacher tasks across medium, medium-replay, and medium-expert datasets, and a Key-to-Door task requiring long-term credit assignment, with comparisons to methods such as Conservative Q-Learning, REM, and behavior cloning.
Key findings indicate that the resulting Decision Transformer model performed comparably or better than state-of-the-art baselines on most tasks, achieving gamer-normalized scores competitive with or above CQL on three of four Atari games and the highest average normalized scores across Gym settings. It excelled in sparse-reward and long-horizon credit assignment scenarios, where temporal difference methods collapsed, and demonstrated the ability to generate trajectories closely matching specified target returns, including some extrapolation beyond dataset maxima. Longer context lengths improved performance, and the model avoided the need for explicit value pessimism or behavior regularization.
These results suggest that sequence modeling can serve as a simpler, scalable alternative to conventional RL algorithms by directly leveraging advances from language modeling, potentially reducing sensitivity to reward density and improving robustness in data-limited regimes. The approach may lower barriers to applying large-scale Transformer techniques in decision-making domains while highlighting opportunities to bypass some instabilities of bootstrapped value estimation.
Actionable next steps supported by the work include integrating the model into online RL pipelines as a behavior generator alongside exploration methods, applying self-supervised pretraining on larger datasets, and testing more sophisticated embeddings for stochastic settings. Further investigation is needed to characterize failure modes in Markov decision processes and assess risks from biases in training data before broader deployment.
Limitations include evaluation on a restricted set of benchmarks and dataset sizes, with performance in very low-data regimes or real-world MDPs remaining uncertain; confidence is moderate for the reported domains given consistent multi-seed results but should be tempered for generalization beyond the tested environments.
- Paper: Offline Reinforcement Learning: Tutorial, Review, and Perspectives on Open Problems, Sergey Levine et al. (2020). This foundational tutorial formalizes the core challenges of offline reinforcement learning—such as distributional shift and value overestimation—that Decision Transformer aims to bypass.
- Paper: Conservative Q-Learning for Offline Reinforcement Learning, Aviral Kumar et al. (2020). It introduces Conservative Q-Learning, the primary state-of-the-art offline temporal difference baseline benchmarked against Decision Transformer.
- Paper: Off-Policy Deep Reinforcement Learning without Exploration, Scott Fujimoto et al. (2018). This paper analyzes the fundamental failure modes of standard off-policy algorithms on fixed datasets, motivating the non-bootstrapped sequence modeling formulation.
- Paper: Generative Adversarial Imitation Learning, Jonathan Ho et al. (2016). It establishes foundational principles for learning decision policies from demonstration data without explicit environment rewards, providing essential background for trajectory-conditioned learning.
- Paper: Human-level control through deep reinforcement learning, Volodymyr Mnih et al. (2015). It provides the benchmark context and standard replay buffer sources for the Atari environments evaluated in the paper.
- Paper: RT-1: Robotics Transformer for Real-World Control at Scale, Anthony Brohan et al. (2023). It scales sequence-modeling architectures like transformers from simulated benchmarks directly to large-scale real-world robotic control policies.
- Paper: Diffusion policy: Visuomotor policy learning via action diffusion, Cheng Chi et al. (2023). It explores generative trajectory modeling for offline visuomotor policy learning via conditional diffusion, extending generative sequence approaches beyond autoregressive transformers.
- Paper: π0: A Vision-Language-Action Flow Model for General Robot Control, Kevin Black et al. (2024). It advances generalist robot control by coupling pre-trained vision-language representations with continuous action generation models trained on extensive offline datasets.
- Paper: Recurrent Looped Transformer, Yifan Zhang (2026). It investigates recurrent and looped transformer architectures to support extended temporal sequences and persistent policy execution during reinforcement learning rollouts.
- Paper: Sample-Efficient Learning from Agent Experience, Chenhui Gou et al. (2026). It studies how to distill long-horizon agent trajectories and decision contexts into model weights without requiring continuous environment interaction.
