Anthropic has started embedding watermarks in Claude’s output, a move driven by EU AI Act compliance but applied globally since the company can’t restrict the feature by region. The system, based on Google’s SynthID-Text approach, tweaks the randomness source during word selection to create a statistically detectable pattern—no visible marks, no hidden characters, just subtle shifts in which words get picked. All Claude models released after August 2 carry the marking, with older versions to be retrofitted in the coming months.
John Gruber isn’t buying the company’s claim that the watermark is imperceptible. The Daring Fireball blogger—who’s been running the influential tech blog since 2002 and co-created Markdown—argues that no two synonyms carry identical meaning. When Claude picks between ‘overcast’ and ‘grey’ based on a secret watermark key rather than semantic precision, text quality inevitably suffers. The system sometimes boosts the probability of a worse word and lowers it for the best one, he writes. He even suggests Gemini’s reputation as weaker than Claude and ChatGPT could partly stem from SynthID already being active in Google’s model.
For law firms, the practical impact is mostly a non-issue, according to legal trade publication Artificial Lawyer. Most clients and courts wouldn’t object to AI use, and some clients are actively requesting it. But the watermark travels with text in ways that could get awkward. A contract might contain AI-marked clauses alongside human-written ones, and future documents built on older templates carry those markings forward indefinitely. If multiple LLMs are used, different watermarks could overlap in a single document.
Fee negotiations are where things could get uncomfortable. If a client demands a discount because AI made the work easier, the AI contribution is now verifiable in principle. And for firms whose clients explicitly ban AI use, a factually flawless document could still be proven AI-assisted. Anthropic notes that watermarking is sparser in fact-heavy passages since fewer word alternatives exist—relevant for legal texts that depend on precision. Meanwhile, tools like Declaude can strip the markings entirely, which its developer James Padolsey points out means the system mostly hits ordinary users while doing little against deliberate circumvention.
