Watermarks changed six of seven tool callers

Lasso Security’s SynthID-Text study found watermarking reduced tool-call accuracy on six of seven open-weight models and produced 6.5% average verdict churn across 21 model-temperature combinations. The original study also reports Gemma 3 27B refusal churn rising from 6.0% to 23.5% under prompt injection, while noting the experiment did not test Claude’s planned implementation; Ars Technica’s coverage lays out the study’s limits. Treat provenance as part of deployed behavior: rerun tool and refusal evaluations whenever watermarking or its key changes, as the archive’s Claude watermark analysis argues.