Ada-RS: Adaptive Rejection Sampling for Selective Thinking

• URL: http://arxiv.org/abs/2602.19519v1
• Date: Mon, 23 Feb 2026 05:20:15 GMT
• Title: Ada-RS: Adaptive Rejection Sampling for Selective Thinking
• Abstract summary: Large language models (LLMs) are increasingly being deployed in cost and latency-sensitive settings.<n>We study selective thinking for tool-using LLMs and introduce Adaptive Rejection Sampling (Ada-RS)<n>Ada-RS scores multiple sampled completions with an adaptive length-penalized reward then applies rejection sampling to retain only high-reward candidates.
• Score: 8.760287445955045
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: Large language models (LLMs) are increasingly being deployed in cost and latency-sensitive settings. While chain-of-thought improves reasoning, it can waste tokens on simple requests. We study selective thinking for tool-using LLMs and introduce Adaptive Rejection Sampling (Ada-RS), an algorithm-agnostic sample filtering framework for learning selective and efficient reasoning. For each given context, Ada-RS scores multiple sampled completions with an adaptive length-penalized reward then applies stochastic rejection sampling to retain only high-reward candidates (or preference pairs) for downstream optimization. We demonstrate how Ada-RS plugs into both preference pair (e.g. DPO) or grouped policy optimization strategies (e.g. DAPO). Using Qwen3-8B with LoRA on a synthetic tool call-oriented e-commerce benchmark, Ada-RS improves the accuracy-efficiency frontier over standard algorithms by reducing average output tokens by up to 80% and reducing thinking rate by up to 95% while maintaining or improving tool call accuracy. These results highlight that training-signal selection is a powerful lever for efficient reasoning in latency-sensitive deployments.

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