The company says all Claude models launched on or after August 2, 2026, support the technology from launch. Anthropic says supported models produce marked text when accessed through Claude, Claude Code, Cowork, its API and third-party cloud platforms. Ironically, a Claude watermark doesn't prove Claude wrote itThere is, however, a rather substantial caveat. Probably notThat essentially brings us back to square one because the presence, or lack thereof, of the Claude watermark proves nothing. For now, perhaps the biggest unanswered question is what Claude’s invisible text marking actually consists of.