AI Text Watermarking and Quality Loss: SynthID-Text Weakens Response Diversity in Multi-Turn Generation

Keyvan's blog post argues that the claim in the Anthropic and Google SynthID-Text papers that "watermarking does not affect output quality" is based only on tests of single responses and does not cover multi-turn conversations or multiple-retry scenarios. The article cites the "diversity/detectability trade-off" in the SynthID-Text supplementary materials, pointing out that watermarking makes multiple responses to the same prompt more similar, potentially reducing the overall quality of generate-then-select systems. The article also cites a reproduction experiment by technical consultant Natzir Turrado: the watermarked model described a trip to a seaside town five times, with four openings nearly identical, while the unwatermarked model produced three different openings.