[Feature]: Built-in watermarking support for EU AI Act Article 50(2)

[yoonhyunwoo]

🚀 The feature, motivation and pitch

EU AI Act Article 50(2) took effect on 2 August 2026. It requires providers of generative AI systems to mark outputs in a machine-readable format and make them detectable.

For providers serving models via vLLM, is there a plan to add built-in watermarking support to help meet this requirement?

Alternatives

It is possible to implement the Kirchenbauer et al. (2023) green/red-list scheme via a custom logits_processor.

Additional context

• Kirchenbauer et al. (2023), arXiv:2301.10226
• docs: EU AI Act compliance guide for vLLM deployers #37862 — EU AI Act compliance guide for vLLM deployers
• EC Code of Practice on Transparency of AI-Generated Content
• Reference implementation: https://github.com/yoonhyunwoo/vllm/tree/feat/watermark

[Yusufchy]

Built-in support would be valuable, but the API shape matters: watermark configuration should be explicit per request or model, deterministic under sampling settings, and observable in logs so operators can prove which policy was applied. It would also help to document false-positive and quality trade-offs, plus how batch and streaming outputs preserve detection metadata.

[tjwebb]

This should not be a core feature of the engine.