arXiv AI

TextSeal2: Distortion-Free LLM Watermarking with Copula Mixing and Memoryless Races

TextSeal2 is a distortion‑free watermarking method for large language models that maintains signal integrity during speculative decoding. It merges multiple keys into a single virtual key using a Gaussian copula, ensuring that the acceptance rate and output diversity remain unchanged while adding no measurable inference latency. Experiments on three LLMs show that TextSeal2 detects 8–22 percentage points more 100‑token answers than its predecessor TextSeal and outperforms textGrain under speculative decoding, all without post‑logits optimization.

arXiv AI
Oct 31

Only Accepted Tokens Count: An Energy Accounting of Speculative Decoding Under Latency Targets

The paper investigates how speculative decoding—where a draft model proposes multiple future tokens that are then verified by the target model—affects energy consumption in large language model serving under latency constraints. It finds that energy savings depend heavily on the acceptance rate of drafted tokens, which varies by model architecture, drafting scheme, and the type of text (e.g., conversation vs. code, English vs. Romansh). The study shows that while speculation can reduce energy per token at small batch sizes, at larger batches the verification cost dominates, potentially turning speculation into an energy loss, especially when acceptance rates are low.

By Bole Ma, Ayesha Afzal, Jan Eitzinger, Harald Koestler, Gerhard Wellein
arXiv AI
Oct 9

Speedbumps: Rejection Attacks on Speculative Decoding

Speedbumps: Rejection Attacks on Speculative Decoding explores how Speculative Rejection Attacks (SRAs) can degrade the efficiency of speculative decoding by causing draft and target models to disagree more often, leading to more target-model forward passes per token. The authors introduce two attacks—Speedbump-P and Speedbump-D—that append adversarial suffixes to attacker-controlled content, optimizing the expected length of the accepted speculative prefix. In some scenarios, these attacks slow inference below autoregressive decoding, reduce output quality, yet remain effective under sampling and transfer across drafters or target models sharing a drafter.

By Adam Y. J. Jones, Yu Yuan, Sergio Maffeis
arXiv Machine Learning
Oct 23

MarkTune: Improving the Quality-Detectability Trade-off in Model-Embedded LLM Watermarking

MarkTune is a model‑embedded watermarking framework that improves the trade‑off between generation quality and detectability. By regularizing toward a high‑quality reference distribution, it decouples quality preservation from proximity to the base model and uses the GaussMark detection statistic as a reward during on‑policy fine‑tuning. Empirical results show that MarkTune enhances the quality‑detectability frontier, maintains downstream task performance, and remains robust against text‑editing and open‑weight attacks across diverse datasets.

By Yizhou Zhao, Zhiwei Steven Wu, Adam Block
arXiv Machine Learning
Jul 14

One Token Is Enough: Fingerprinting and Verifying Large Language Models from Single-Token Output Distributions

arXiv:2607. 10252v1 Announce Type: cross Abstract: Large language models (LLMs) are increasingly consumed through opaque serving chains - API aggregators, resellers, and inference providers - in which the client has no technical means to confirm that the model answering is the model advertised, and recent audits show that a substantial fraction of commercial endpoints deviate from the vendor's reference weights.

By Tomas Bruckner
arXiv Computation and Language
Oct 19

Watermarkability: Measuring and Improving Language-Model Compatibility with Logit-Based Watermarks

The paper introduces "watermarkability," a metric that quantifies how compatible a language model is with a logit‑based watermark that boosts the probability of a specified token set during decoding. By measuring the expected minimum KL divergence needed to achieve a target probability mass, the authors can assess and compare models and watermark rules. They propose a two‑stage approach—first training a low‑rank adapter conditioned on the target set, then applying a minimal uniform logit bias—to reduce this cost, achieving significant perplexity reductions across multiple watermark schedules on OPT‑125M and Qwen3‑8B.

By Zewei Deng, Mohamed Seif, Liyan Xie