REVIEW 3 major objections 6 minor 24 references
Benchmarking Partial Observability in Reinforcement Learning with a Suite of Memory-Improvable Domains
T0 review · 3 major / 6 minor · reviewed 2026-08-06 · deepseek-v4-flash
Pith's one-line read The paper argues that a usable partial-observability benchmark needs broad coverage across forms of state aliasing plus a clear floor-to-ceiling performance gap, and introduces POBAX, a JAX suite whose tasks are all memory improvable and…
desk verdict A useful JAX benchmark and a sensible selection criterion, but the 'all environments memory improvable' claim is confounded by architecture mismatches in five of eleven tasks. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The mechanism that carries the argument is the memory improvability gap: the difference in return between an agent fed partial observations and an agent fed a richer state representation (or an optimal belief policy), with the learning algorithm, network size, and other hyperparameters held fixed. The formal setting is the POMDP, whose observation function $\Phi : S \to \Delta\Omega$ maps hidden states to incomplete observations, and whose memory functions $\mu(h_t)$ condense the history $h_t = (o_t, a_t, \ldots, o_0, a_0)$ into a fixed-size memory state. The paper also contributes an eight-category taxonomy of partial observability—noisy state features, visual occlusion, object uncertainty and tracking, spatial uncertainty, moment features, unknown opposition, episode nonstationarity, and needle-in-a-haystack tasks—and selects at least one representative environment per category so the suite has coverage as well as signal. The gap is the instrument: a large floor-to-ceiling distance means added memory is what would close the distance, so an improvement by a memory-based algorithm is attributable to mitigating partial observability rather than to a better function approximator.
What would settle it
Retrain the full-state ceiling agents for RockSample(11,11), RockSample(15,15), velocity-only Walker and HalfCheetah, and no-inventory Crafter with the same memoryless MLP used for the observation-only floor; if the performance gap largely collapses or reverses, those environments' memory improvability is an artifact of function approximation power rather than a signal about partial observability.
Extended reading notes
Core claim
The paper's central claim is that all POBAX environments are memory improvable and require hard-to-learn memory functions. Memory improvability is the existence of a performance gap between an observations-only agent (the floor) and an agent that receives more state information (the ceiling), all other factors roughly equal; the paper verifies this gap with 30-seed experiments across T-Maze, RockSample(11,11), RockSample(15,15), Battleship, velocity-only Walker and HalfCheetah, two DeepMind Lab MiniGrid mazes, pixel-based Ant and HalfCheetah, and no-inventory Crafter. In every environment three memory-based algorithms—recurrent PPO, $\lambda$-discrepancy with recurrent PPO, and Transformer-XL—improve on the observation-only agent and land below the full-state agent, which the authors read as evidence that the gains come from mitigating partial observability rather than from function approximation or hyperparameters. The suite is implemented entirely in JAX, and the paper supplies recommended per-environment hyperparameters so the floor and ceiling can be reproduced out of the box.
Load-bearing premise
The load-bearing premise is that the gap between the observation-only floor and the full-state ceiling measures hidden information rather than architectural power, because in several environments the ceiling agent uses a recurrent or transformer network while the floor agent uses a memoryless multilayer perceptron.
Editorial extensions
If this is right
- Researchers can benchmark new history-based algorithms out of the box: POBAX ships recommended hyperparameters for every environment, and the floor-to-ceiling gap is the declared measure of progress.
- An algorithm that substantially closes the memory improvability gap has positive evidence that its gains come from mitigating partial observability, because the gap is constructed to hold architecture and hyperparameters fixed.
- The gap size becomes a diagnostic: a large gap tells a practitioner that adding an RNN, transformer, or other memory mechanism is likely to pay off, while a small gap signals that memory is not the bottleneck.
- Because every environment runs in JAX and scales on GPU, researchers can afford the large hyperparameter sweeps the paper shows are needed for reliable floor and ceiling curves.
- The eight-category taxonomy gives benchmark designers a coverage checklist when assembling or extending their own partial-observability suites.
Reading between the lines
- A natural extension is to make the memory-improvability test a gate for admitting new tasks to the benchmark: compute the floor-ceiling gap under a fixed architecture budget and keep only environments where the gap is large and positive.
- The paper suggests, though it does not test, a stronger claim: an algorithm that performs well across all POBAX categories simultaneously—pixels, sparse rewards, long horizons, object tracking—should transfer better to real deployments, which usually mix several forms of partial observability at once.
- A stricter benchmark variant would require the floor and ceiling to share the same network family; testing whether the improvability gaps survive that constraint would separate the information gap from the function-approximation gap.
- If the paper's reasoning is right, a memory-algorithm result published without its floor and ceiling curves cannot be attributed to memory; making all three curves a reporting norm would make benchmark comparisons decisive.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper argues that a partial-observability benchmark should satisfy two properties: coverage of diverse forms of state aliasing, and a memory-improvability signal defined as a performance gap between agents with more versus less state information when other factors are held roughly equal. It introduces POBAX, a JAX-based suite containing T-Maze, RockSample(11,11), RockSample(15,15), Battleship, Walker-V, HalfCheetah-V, two DeepMind Lab MiniGrid mazes, two visual Mujoco tasks, and No-inventory Crafter. The paper categorizes partial observability into eight forms, reports ablations on the number of parallel environments and network width, recommends per-environment hyperparameters, and evaluates recurrent PPO, λ-discrepancy PPO, and Transformer-XL with 30-seed confidence intervals. The central claim is that all POBAX environments are memory improvable and require hard-to-learn memory functions.
Significance. If the central claim holds, POBAX would be a valuable community resource: it covers several distinct forms of partial observability, is implemented entirely in JAX for GPU-scalable experimentation, ships with recommended hyperparameters, and provides extensive baselines. The paper's strengths include the open-source release, the detailed appendices, the systematic hyperparameter sweeps, the 30-seed confidence intervals, and the explicit investigation of confounding factors such as parallel-env count and network width. The timing experiments in Appendix A also support the scalability argument. However, the suite-level memory-improvability claim is only as strong as the floor/ceiling comparisons, and several of those comparisons do not satisfy the paper's own 'all other factors roughly equal' condition.
major comments (3)
- [§6.1, §6.2, App. C.3/C.5/C.8] The central claim that all POBAX environments are memory improvable is not established for five of the configurations. For RockSample(11,11) and RockSample(15,15), Appendix C.3 states that the perfect-memory agent was trained with an RNN rather than a memoryless MLP; for Walker-V and HalfCheetah-V, Appendix C.5 states that an RNN was used for the fully observable results; and for No-inventory Crafter, Section 6.2 states that the 'full state' agent is a transformer trained on regular Crafter observations with the inventory included. The observation-only floors in Figure 6 are memoryless MLPs. Under the Section 4 definition, memory improvability requires a gap with 'all other factors roughly equal,' and an RNN or transformer ceiling does not satisfy that condition, since the gap may reflect greater function-approximation capacity rather than additional state information. The appendix disclosures do not repair the abstract's unqualified claim. Please rerun these ceilings with a memoryless MLP, or otherwise match the architecture between floor and ceiling, or restrict the memory-improvable claim to the configurations without this confound.
- [§6.2, Fig. 6, App. C.4] For Battleship, the green 'STATE' ceiling in Figure 6 is not a neural agent trained with more state information; it is the mean return of an optimal belief-state policy computed programmatically. The floor is a memoryless PPO agent trained from hit/miss observations. The gap between an optimal solver and a sample-based learner can be large even in the absence of partial observability, due to sample complexity, exploration difficulty, or optimization error. This violates the Section 4 requirement that other factors be roughly equal, in a different way from the architecture mismatch. Please add a trained ceiling using the same PPO learning setup with full-state or perfect-memory observations, and report the optimal belief policy as a separate reference line rather than as the 'STATE' ceiling.
- [Abstract, §6, Fig. 6] The abstract and Section 6 assert that the POBAX tasks require hard-to-learn memory functions, but the paper never defines or operationalizes hardness. The only supporting evidence offered is that the three memory-based algorithms improve over the observation-only floor and underperform the ceiling. Given the architecture and ceiling mismatches described above, that evidence does not establish hardness. Please provide an operational criterion for 'hard-to-learn'—for example, required memory length, information-theoretic complexity, or the number of training steps needed to close a fixed fraction of the gap—and report it per environment.
minor comments (6)
- [Abstract] The phrase 'performance of a agents' should be 'performance of agents'.
- [§3.2] The sentence 'In Figure 3 investigate the effect of network width' is missing a subject; it should read 'In Figure 3 we investigate'.
- [App. C.3] The sentence 'avoid all the back ones' appears to be a typo for 'avoid all the bad rocks.'
- [App. C.5] The exact masked features for each masked-control environment are not specified in the appendix; the text directs readers to the code repository. Since the information content of the floor and ceiling observations is central to the paper's claims, please list the observation vectors explicitly.
- [App. C.7] The architecture used for the fully observable ceiling in the visual Mujoco environments is not stated. Please specify explicitly whether that ceiling uses a memoryless MLP, an RNN, or a transformer.
- [§6.2] For No-inventory Crafter, the curve labeled 'STATE' in Figure 6 is actually the regular Crafter observation with the inventory visible, not the underlying environment state; please relabel this curve in the figure and caption to avoid confusion.
Circularity Check
No significant circularity: the memory-improvability claims are empirical benchmark measurements, not derivations from fitted inputs or self-citations.
full rationale
The paper's central claim—that all POBAX environments are memory improvable—is an empirical measurement of a performance gap between baseline and ceiling agents, not a quantity derived from fitted parameters or from a self-citation. No equation reconstructs the gap by construction; the recommended hyperparameters are chosen so that baseline and skyline agents 'both learn' (Section 3.1), not to force a target gap. The λ-discrepancy algorithm (Allen et al., 2024) is co-authored by an author of this paper, but it is evaluated alongside recurrent PPO and Transformer-XL, and the benchmark's utility does not depend on λ-discrepancy winning. The appendix disclosures that the full-state ceiling for RockSample, Masked Mujoco, and no-inventory Crafter uses an RNN or transformer while the observation-only floor uses a memoryless MLP (C.3, C.5, C.8) are genuine confounds for the 'all other factors roughly equal' criterion, but they are validity concerns, not circular reductions: the gap is not constructed to equal a fitted value, and the paper does not hide the difference. There is no self-citation chain invoked as an external uniqueness theorem, and no known result is renamed as a derivation. The honest finding is no significant circularity.
Assumptions & free parameters
free parameters (6)
- per-environment hidden_size =
32 for T-Maze, 256 for RockSample 11 and masked control, 512 for RockSample 15, DMLab, visual control, Crafter
- per-environment num_envs =
4 default; 8 for RockSample 11; 16 for RockSample 15; 32 for Battleship; 256 for DMLab-01 and Crafter; 512 for DMLab-02
- algorithm learning rate and GAE lambda =
swept per algorithm, e.g., lr in {2.5e-3, 2.5e-4, 2.5e-5, 2.5e-6}, lambda0 in {0.1, 0.3, 0.5, 0.7, 0.9, 0.95}
- lambda-discrepancy beta and lambda1 =
beta in {0.25, 0.5}, lambda1 in {0.5, 0.7, 0.95}
- entropy coefficient =
0.01 default; 0.05 for Battleship; 0.2 for RockSample
- transformer embed size / qkv features =
256 default, 220 or 96 in some environments
assumptions (4)
- standard math The POMDP formalization with observation function Phi is the right model for the environments
- domain assumption If agents with more state information outperform agents with less, under otherwise equal conditions, then memory can improve performance
- domain assumption The eight listed categories of partial observability adequately span the forms relevant to RL benchmarks
- domain assumption The failure of tested memory algorithms to fully close the floor-ceiling gap indicates the memory function is hard to learn
Cite this review
Pith. "Pith review of Benchmarking Partial Observability in Reinforcement Learning with a Suite of Memory-Improvable Domains." pith.science (2026). https://pith.science/paper/RDSNABQB
@misc{pith2026250800046,
author = {Pith},
title = {Pith review of: Benchmarking Partial Observability in Reinforcement Learning with a Suite of Memory-Improvable Domains},
year = {2026},
howpublished = {\url{https://pith.science/paper/RDSNABQB}},
note = {Machine review of arXiv:2508.00046}
}
read the original abstract
Mitigating partial observability is a necessary but challenging task for general reinforcement learning algorithms. To improve an algorithm's ability to mitigate partial observability, researchers need comprehensive benchmarks to gauge progress. Most algorithms tackling partial observability are only evaluated on benchmarks with simple forms of state aliasing, such as feature masking and Gaussian noise. Such benchmarks do not represent the many forms of partial observability seen in real domains, like visual occlusion or unknown opponent intent. We argue that a partially observable benchmark should have two key properties. The first is coverage in its forms of partial observability, to ensure an algorithm's generalizability. The second is a large gap between the performance of a agents with more or less state information, all other factors roughly equal. This gap implies that an environment is memory improvable: where performance gains in a domain are from an algorithm's ability to cope with partial observability as opposed to other factors. We introduce best-practice guidelines for empirically benchmarking reinforcement learning under partial observability, as well as the open-source library POBAX: Partially Observable Benchmarks in JAX. We characterize the types of partial observability present in various environments and select representative environments for our benchmark. These environments include localization and mapping, visual control, games, and more. Additionally, we show that these tasks are all memory improvable and require hard-to-learn memory functions, providing a concrete signal for partial observability research. This framework includes recommended hyperparameters as well as algorithm implementations for fast, out-of-the-box evaluation, as well as highly performant environments implemented in JAX for GPU-scalable experimentation.
Figures
Figures from the paper (5 more)
Reference graph
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Unless otherwise specified, these default parameters were used in every experiment. We also note that unless otherwise stated, the “fully observable” agent was trained with a memoryless MLP. We begin with a discussion on differences observed between our results and other benchmark results in partial observability, then elucidate the full details of each e...
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Reviewed August 6, 2026 · model on record in the stance chip above.
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