Anthropic to Add Invisible Text Watermarks to Future Claude Models

The watermarking rolled out because Anthropic signed the EU AI Act’s Article 50(2) Code of Practice, and — like you note — the marking applies globally, not just to EU users. That’s the Brussels Effect working exactly as it usually does: it’s cheaper and more consistent to build one system than maintain a segmented one. [...] ChatGPT: I would phrase that cautiously. OpenAI has committed publicly to complying with the requirements that apply to its products, and it has endorsed the EU Code of Practice. But I cannot point to a public OpenAI commitment saying, specifically, “text watermarking will be deployed by December 2026.” Its current wording is that it is working to expand provenance measures “across modalities, including text, as standards and tooling continue to mature.” As for separate EU and non-EU versions, I don’t know of any announced plan to do that. In fact, OpenAI’s existing provenance measures—C2PA and SynthID for images, and watermarking for supported audio—are being dep

detection tool (Google Cloud, nd). The open-source model developers Stability AI and Black Forest Labs (together with their partners) also integrate invisible watermarking techniques in (some of) their models (Stability AI, ndb; AI, 2024). They use an open-source watermarking library that includes both a watermarking encoding and decoder algorithm (Stability AI, nda; ShieldMnt, nd; Black Forest Labs, 2025). Additionally, several organisations are offering API-based solutions or open-source tools that allow others to embed post-generation invisible watermarks to their images (IMATAG, nd; Hugging Face, ndc). [...] These organisations thus become both the provider and deployer of the generative AI system under our interpretation of the AI Act, which requires compliance with both transparency requirements. The dual role of model and system developer would allow such organisations to implement robust watermarking techniques in the model development phase (such as embedding initial noise pat

# How Claude marks AI-generated content Anthropic has signed the EU AI Act's Article 50(2) Code of Practice on Transparency of AI-Generated Content, as a provider of both generative AI models and generative AI systems. This article describes how we’re planning to put those commitments into practice, how marking works, and what its limitations are. We’ll update this article and publish more detailed technical guidance as it becomes available. Anthropic’s commitments under the EU AI Act’s Code of Practice on Transparency of AI-Generated Content What our marking commitments mean for Claude:

## Why are you watermarking Claude’s outputs? We’re implementing watermarking to comply with the EU AI Act. Anthropic, along with several other major AI model providers and around 190 total signatories, signed the EU Code of Practice on Transparency of AI-Generated Content in July 2026. This requires AI system providers to use methods of “marking” AI-generated text. We’re applying watermarking globally at launch because we don't yet have a durable way to scope it by region. However, we will continue to evaluate different approaches, and will share updates when we have them. ## Other questions ### How do I check if a piece of text was written by Claude? We will soon be offering a watermark detection API. We’re in the process of working out the details of its implementation. [...] # How Claude’s text watermark works How Claude’s text watermark works Future Claude models will generate text that contains a watermark. This is a way of determining the likelihood that Claude was involve

Katherine Forrest: Right. And so Google, for example, which has tied its C2PA and SynthID work directly to their compliance with the EU AI Act and the code of practice, they've already got it sort of baked in. And Anthropic's announcement about watermarking that we started this episode with actually did the same. Scott Caravello: Right. And so the guidelines, which cover a lot of ground and not just this specific watermarking issue that we've been talking about a lot today, they don't endorse a single technical solution, right. But what's interesting, and I guess I wanted to flag, is that the carve-outs where it says that the compliance is not necessary line up with some of the limitations of this text watermarking solution that we discussed. [...] Scott Caravello: Exactly. And so then sort of going a level deeper on these requirements under the EU AI Act, there are these codes of practice, which we've talked about in other contexts, but basically they're a voluntary set of guidelines

2K @AnthropicAI Anthropic @AnthropicAI We’ve written an FAQ to answer some of the questions we've received about watermarking. In summary: • We’re implementing watermarking to comply with the EU AI Act. Other major model developers have signed the same Code of Practice and will also be implementing watermarking; • Our watermarking method doesn’t have any practical impact on the quality or content of Claude’s outputs; • The difference between watermarked and un-watermarked text will not be distinguishable to readers; • Nothing is added to the text and there are no hidden characters; • Watermarking doesn’t require extra tokens, and will not be more expensive; • Watermarks can’t be traced to a specific person, organization, or chat. Read more: anthropic.com/news/claude-te… [...] @AnthropicAI Anthropic @AnthropicAI We’ve written an FAQ to answer some of the questions we've received about watermarking. In summary: • We’re implementing watermarking to comply with the EU AI Act.