On Regret Bounds of Thompson Sampling for Bayesian Optimization

Shion Takeno; Shogo Iwazaki

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arXiv · 2603.09276

On Regret Bounds of Thompson Sampling for Bayesian Optimization

Shion Takeno·Shogo Iwazaki

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Abstract

We study a widely used Bayesian optimization method, Gaussian process Thompson sampling (GP-TS), under the assumption that the objective function is a sample path from a GP. Compared with the GP upper confidence bound (GP-UCB) with established high-probability and expected regret bounds, most analyses of GP-TS have been limited to expected regret. Moreover, whether the recent analyses of GP-UCB for the lenient regret and the improved cumulative regret upper bound can be applied to GP-TS remains unclear. To fill these gaps, this paper shows several regret bounds: (i) a regret lower bound for GP-TS, which implies that GP-TS suffers from a polynomial dependence on $1/\delta$ with probability $\delta$, (ii) an upper bound of the second moment of cumulative regret, which directly suggests an improved regret upper bound on $\delta$, (iii) expected lenient regret upper bounds, and (iv) an improved cumulative regret upper bound on the time horizon $T$. Along the way, we provide several useful lemmas, including a relaxation of the necessary condition from recent analysis to obtain improved regret upper bounds on $T$.

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Shion Takeno, Shogo Iwazaki. 2026-03-10. On Regret Bounds of Thompson Sampling for Bayesian Optimization. https://arxiv.org/abs/2603.09276

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