Stealth Model
also called Anonymous preview, Cloaked model, Alpha listing
A model released under a codename, with no lab attached, to be judged on behaviour alone.
A model made available through a gateway or API under a playful codename, with the developing lab deliberately unnamed. Users get the model and its spec — usually free, for a limited preview — but no vendor, model card or benchmark sheet. The point is to collect real usage and unbiased first impressions before the lab puts its name on it.
The lifecycle repeats: codename launch, free usage at scale, community fingerprinting, then reveal under the real name and a move to a paid, named ID. The codename listing is temporary by design — anything that hardcodes it should expect to break or start costing money.
Fingerprinting is real evidence but limited evidence. Matching a tokenizer, error payloads or knowledge cutoffs establishes shared serving infrastructure, not model identity: one lab can serve two different checkpoints from the same stack, and the crowd’s first guess has been wrong before. Read the gateway’s stealth terms too — prompts may be retained, and may be used for training.
The track record says to plan for a reveal: of thirteen tracked stealth listings, seven were eventually claimed by a lab, and the free window usually closed at reveal. Ox Alpha lasted about six days before Z.ai named it GLM-5.3-Flash. Space Bunny, listed September 23, 2026, was still unclaimed when OpenRouter’s preview ended October 5, with OpenCode extending free access.
The trial that became a dependency
A team builds a feature on a free stealth listing because it tops their quick tests.
At reveal the codename listing stops and the model moves to a paid, named ID. The team scrambles to re-benchmark and re-price. The fix is the one the gateway guides give: keep the model ID in config, keep a small eval set, and know your fallback before you ship.
Treating a fingerprint as proof of identity, or treating a stealth listing as a permanent free tier. Both have bitten people.
- reportOpenRouter Stealth Models: Who They Turned Out to Be ↗
A census of OpenRouter stealth listings with reveal outcomes: Quasar Alpha to GPT-4.1, Pony Alpha to GLM-5, Ox Alpha to GLM-5.3-Flash, and the ones never officially revealed.
- reportSpace Bunny Alpha: The Stealth Model and the MiniMax Clues ↗
A launch record for the September 2026 Space Bunny listing, including the independent tokenizer tests pointing at the MiniMax family and the explicit warning that the MiniMax link is unconfirmed.
- reportOx Alpha: the cloaked 1M-context model on OpenRouter, and what the forensics actually show ↗
Forensic write-up of the Ox Alpha fingerprinting, with a base-rate table of earlier stealth launches — including the cases where the crowd’s first guess was wrong.
Benchmark
A shared public test used to compare models.
Benchmark Contamination · Test set leakage
The test set was in the training data.
Model Provider
The company or platform you call to run inference.
Model Routing
Sending each request to the cheapest model that can handle it.
Evaluation · Evals
How you know the system is actually working.