Anthropic starts watermarking everything Claude writes

Every Claude model launched on or after August 2, 2026 now weaves an imperceptible watermark into its generated text and attaches signed C2PA provenance metadata to generated files. The marking applies worldwide, including outside the EU, across Claude, Claude Code, Claude Cowork, the API, and cloud partners AWS, Google Cloud, and Microsoft Foundry. It is triggered by the EU AI Act's Article 50(2) Code of Practice, which became enforceable August 2; Anthropic says support for older models is coming later. The company is explicit about the limits: a heavily edited, paraphrased, or very short passage may carry no detectable signal, and a detected mark only shows content "may have been processed by Claude," not who wrote the underlying ideas. Simon Willison, in the Hacker News thread, pressed on the question this lane cares about most: whether a precise, developer-directed code edit gets the same statistical nudge as free-form prose, and whether a voluntary mark in a competitive, multi-vendor market just pushes people who want to cheat toward a model that skips it.

Why it matters: This is an infrastructure answer to a question the corpus has tracked since the rust-lang AI policy and ACM Queue's "Eight Myths" piece: once agents destroy the old signal that effort produces polish, what replaces it? Anthropic isn't changing review policy, it's making the artifact self-disclosing. Whether that holds depends on how easy the mark is to strip, and removal tools were already circulating in the thread within hours.