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BOFormer: Learning to Solve Multi-Objective Bayesian Optimization via Non-Markovian RL
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Proposes BOFormer, a Transformer-based generalized DQN that learns a non-Markovian acquisition function for multi-objective Bayesian optimization, trained on synthetic GP functions and transferred zero-shot to synthetic and 3DGS hyperparameter tasks.
Problem
Learned acquisition functions for multi-objective Bayesian optimization suffer from the hypervolume identifiability issue because hypervolume improvement is history-dependent (non-Markovian), so single-step state representations cannot distinguish scenarios.
Approach
Generalized DQN for non-Markovian environments implemented with a Transformer over history, using a domain-agnostic Q-augmented per-candidate observation representation, normalized hypervolume-improvement reward, prioritized trajectory replay, and demo-policy-guided exploration.
Key results
- On synthetic functions, BOFormer achieves the best or within 1% of the best hypervolume on several tasks (e.g., 0.7377 on ARa vs 0.6290-0.7122 for rule-based baselines at step 100), but not on BC.
- On 3DGS hyperparameter optimization, BOFormer is best or near-best on all five scenes (e.g., 0.9508 on Lego and 0.9745 on Ship at step 30).
- Markovian (w=1) BOFormer underperforms non-Markovian variants, supporting that sequence modeling mitigates hypervolume identifiability.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use BOFormer instead of the strongest listed baseline | MOBO optimization · AR, ARa, RBF, Chairs, Lego, Materials, Ship | hypervolume: 0.5787 -> 0.5900; 0.7122 -> 0.7377; 0.8731 -> 0.8751; 0.9159 -> 0.9162; 0.9409 -> 0.9508; 0.9217 -> 0.9224; 0.9661 -> 0. | Helped |
| Use BOFormer instead of the strongest listed baseline | MOBO optimization · BC, DRa, Matern, BCD, Mic | hypervolume: 0.4773 -> 0.4476; 0.9573 -> 0.9461; 0.8696 -> 0.8642; 0.3697 -> 0.3617; 0.8871 -> 0.8816 | Hurt |
| Add Q-augmented observation representation (ablation) | BOFormer, compared with QT without Q-augmented representation · Synthetic functions | hypervolume | Mixed |
| Use non-Markovian sequence length (w > 1) rather than Markovian sequence length (w = 1) (ablation) | BOFormer · MOBO benchmark tasks | hypervolume | Helped |
| Remove temporal information from the representation (ablation) | BOFormer · Training | training loss stability | Hurt |
| Remove both temporal information and positional encoding (ablation) | BOFormer · Training | training loss stability | Hurt |
Surprising findings
- Plain Q-Transformer without Q-augmented representation performs poorly, indicating sequence modeling alone does not guarantee efficient Pareto search.
- The direct implementation with full posterior over all domain points reportedly needs about 75 days of training for 1000 iterations on a 50-point domain.
Limitations
- Performance is not as strong on Branin and Currin functions, attributed to larger lengthscales.
- Continuous high-dimensional domains rely on Sobol-grid approximate maximization, which may be limiting in high dimensions.
- Direct full-domain implementation is computationally infeasible, motivating the domain-agnostic design.
Experimental setup
Datasets: synthetic GP functions HPO-3DGS
Benchmarks: Ackley-Rastrigin Ackley-Rosenbrock Branin-Currin Dixon-Rastrigin RBF Matern Branin-Currin-Dixon HPO-3DGS
Metrics: attained hypervolume simple regret performance profiles
Baselines: qNEHVI qParEGO NSGA-II qHVKG JES FSAF Decision Transformer Q-Transformer OptFormer
Builds on: DQN DRQN FSAF Decision Transformer Q-Transformer
Closest papers by meaning
- Large Language Models to Enhance Bayesian Optimization (ICLR 2024 · similarity 0.89)
- MOBO-OSD: Batch Multi-Objective Bayesian Optimization via Orthogonal Search Directions (NeurIPS 2025 · similarity 0.87)
- Posterior Inference with Diffusion Models for High-dimensional Black-box Optimization (ICML 2025 · similarity 0.87)
- PG-LBO: Enhancing High-Dimensional Bayesian Optimization with Pseudo-Label and Gaussian Process Guidance (AAAI 2024 · similarity 0.87)
- Latent Bayesian Optimization via Autoregressive Normalizing Flows (ICLR 2025 · similarity 0.87)
- Simple Extensions of Single-Objective Acquisition Functions and Hedge Strategies for Multi-Objective Bayesian Optimization (NeurIPS 2026 · similarity 0.87)
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