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arXiv · 2603.12596

Optimize Wider, Not Deeper: Consensus Aggregation for Policy Optimization

Zelal Su·Mustafaoglu·Sungyoung Lee·Eshan Balachandar·Risto Miikkulainen·Keshav Pingali
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Abstract

Proximal policy optimization (PPO) approximates the trust region update using multiple epochs of clipped SGD. Each epoch may drift further from the natural gradient direction, creating path-dependent noise. To understand this drift, we can use Fisher information geometry to decompose policy updates into signal (the natural gradient projection) and waste (the Fisher-orthogonal residual that consumes trust region budget without first-order surrogate improvement). Empirically, signal saturates but waste grows with additional epochs, creating an optimization-depth dilemma. We propose Consensus Aggregation for Policy Optimization (CAPO), which redirects compute from depth to width: $K$ PPO replicates are optimized on the same batch, differing only in minibatch shuffling order, and then aggregated into a consensus. We study aggregation in two spaces: Euclidean parameter space, and the natural parameter space of the policy distribution via the logarithmic opinion pool. In natural parameter space, the consensus provably achieves higher KL-penalized surrogate and tighter trust region compliance than the mean expert; parameter averaging inherits these guarantees approximately. On continuous control tasks, CAPO outperforms PPO and compute-matched deeper baselines under fixed sample budgets by up to 8.6x. CAPO demonstrates that policy optimization can be improved by optimizing wider, rather than deeper, without additional environment interactions.

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Zelal Su, Mustafaoglu, Sungyoung Lee, Eshan Balachandar, Risto Miikkulainen, Keshav Pingali. 2026-03-13. Optimize Wider, Not Deeper: Consensus Aggregation for Policy Optimization. https://arxiv.org/abs/2603.12596

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