Regret-Based (ε,δ)-optimal Stopping Criteria for Bayesian Optimization
Pith reviewed 2026-05-22 07:19 UTC · model grok-4.3
The pith
Tighter instantaneous regret bounds for GP-UCB enable stopping criteria that guarantee ε-optimal solutions with high probability in Bayesian optimization.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
We present provably tighter instantaneous regret bounds for GP upper confidence bound (GP-UCB) at any given iteration. Then, we propose stopping criteria for GP-UCB based on this tighter bound that ensures an ε-optimal solution with high probability 1-δ upon termination.
What carries the argument
The provably tighter instantaneous regret bound for GP-UCB, which underpins the construction of regret-based (ε,δ)-optimal stopping criteria.
Load-bearing premise
The Gaussian process kernel and the bounded reproducing kernel Hilbert space norm of the objective function satisfy the standard assumptions from the GP-UCB literature.
What would settle it
Run the method on a known test function until the stopping criterion activates and then verify whether the true optimum lies within ε of the reported point with the expected frequency.
read the original abstract
Bayesian optimization (BO) is a widely used iterative black-box optimization method that utilizes Gaussian process (GP) surrogate models. In practice, BO is typically terminated after a fixed evaluation budget is exhausted, which can incur unnecessary cost and provides no optimality guarantee on solution quality. Recent research in developing a practical stopping criterion has made empirical progress, yet a theoretically sound stopping criterion remains a work in progress. In this work, we present provably tighter instantaneous regret bounds for GP upper confidence bound (GP-UCB) at any given iteration. Then, we propose stopping criteria for GP-UCB based on this tighter bound that ensures an $\epsilon$-optimal solution with high probability $1-\delta$ upon termination. Numerical experiments are performed to validate and demonstrate the effectiveness and efficiency of our stopping criteria.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper claims to derive provably tighter instantaneous regret bounds for GP-UCB in Bayesian optimization at any fixed iteration, then proposes stopping criteria based on these bounds that guarantee termination at an ε-optimal solution with probability at least 1-δ. The claims are supported by theoretical analysis building on standard GP assumptions and validated via numerical experiments.
Significance. If the (ε,δ) guarantees are rigorously established, the work would be significant for providing a theoretically grounded alternative to fixed-budget termination in BO, potentially reducing evaluation costs while ensuring solution quality with explicit probabilistic control. This addresses a practical gap in the literature on adaptive BO termination.
major comments (1)
- [Section deriving the (ε,δ) stopping criterion (likely §4 or the main theorem)] The derivation of the stopping criterion applies the per-iteration high-probability instantaneous regret bound directly at the data-dependent stopping time τ. Because τ is a random variable, the event {regret at τ > ε} is not automatically controlled by the fixed-t probability without an additional union bound over possible stopping times, a maximal inequality, or an optional-stopping argument for the underlying martingale. If this correction is absent, the overall failure probability may exceed δ.
minor comments (2)
- [Abstract] The abstract states 'provably tighter' bounds without explicitly identifying the baseline bound from prior GP-UCB analyses to which the improvement is compared.
- [Numerical experiments section] Clarify whether the numerical experiments include ablation on the effect of the tighter bound versus the standard one, and report the observed termination iterations and actual optimality gaps achieved.
Simulated Author's Rebuttal
We thank the referee for their careful reading of the manuscript and for identifying this important technical point regarding the application of our bounds at a random stopping time. We address the comment below and will revise the paper to incorporate a rigorous justification.
read point-by-point responses
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Referee: [Section deriving the (ε,δ) stopping criterion (likely §4 or the main theorem)] The derivation of the stopping criterion applies the per-iteration high-probability instantaneous regret bound directly at the data-dependent stopping time τ. Because τ is a random variable, the event {regret at τ > ε} is not automatically controlled by the fixed-t probability without an additional union bound over possible stopping times, a maximal inequality, or an optional-stopping argument for the underlying martingale. If this correction is absent, the overall failure probability may exceed δ.
Authors: We thank the referee for this insightful observation. Our instantaneous regret bounds are established for each fixed iteration t using standard GP posterior concentration inequalities that hold with probability at least 1-δ. While the stopping time τ is indeed data-dependent, we note that the underlying process can be analyzed via the filtration generated by the observations. In the revised manuscript we will explicitly invoke an optional stopping argument for the relevant martingale (or, equivalently, apply a union bound over a sufficiently fine discretization of possible stopping times up to a practical horizon) to ensure that P(regret(τ) > ε) ≤ δ still holds. This correction will be added to the main theorem and its proof without changing the form of the proposed stopping criterion or the empirical results. revision: yes
Circularity Check
No circularity: stopping criterion derived from per-iteration regret bound under standard GP assumptions
full rationale
The paper derives tighter instantaneous regret bounds for GP-UCB at fixed iterations using standard kernel and RKHS-norm assumptions from prior GP-UCB literature, then defines a stopping rule when the bound drops below ε. This is a direct (if potentially incomplete) implication from the fixed-t high-probability statement to a data-dependent stopping time; no self-definition, no parameter fitted to the target quantity and then renamed as a prediction, and no load-bearing self-citation chain that reduces the central claim to an unverified prior result by the same authors. The derivation chain remains self-contained against external benchmarks.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption Standard assumptions on the Gaussian process kernel and bounded RKHS norm of the objective function as used in prior GP-UCB regret bounds.
Reference graph
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