OpenAI's watermark outs its own unannounced image model

An unannounced OpenAI image model surfaced on LM Arena's blind-test leaderboard, unmasked when a user ran its output through OpenAI's own verification tool. That matters for anyone using LM Arena to judge image models. The board ranks an unreleased entry with no public specs, and OpenAI hasn't said if it ships.

OpenAI didn't announce it, price it, or publish specs. The listing, mona-lisa-1, showed up on the leaderboard with no name tied to OpenAI, no benchmarks, and no documentation attached.

Attribution came from SynthID, the watermarking system OpenAI uses to mark its generated images. A Reddit user ran mona-lisa-1's output back through OpenAI's verification service and got a match, per the r/singularity thread that first flagged it.

Testers on the leaderboard are split. One called mona-lisa-1 "extremely better than Image 2." Others reported visible noise and texture errors in the same outputs.

There's no confirmation of what it becomes. It could ship as GPT Image 3, arrive as a 2.5 update, or stay internal and never launch. OpenAI hasn't said.

SynthID was built to catch misuse of OpenAI's outputs after they leave the building, not to catch OpenAI testing something it hasn't announced. That's what happened here, and it means any future stealth model is one verification check away from the same outcome.

As of August 10, OpenAI still hadn't confirmed what mona-lisa-1 is or whether it ever ships.