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Public story · 2026-08-25 · high
A gzip-based compression test tied the free ox-alpha model to Z.ai's GLM-5.3, and a coding benchmark score backs it up.
Why now: OpenRouter's ox-alpha slot is still live and anonymous, the same listing this fingerprint targets.
Someone on OpenRouter fed ox-alpha, an anonymous model sitting in a free preview slot, its own system prompt back as a user message. The model broke character and named itself GLM, built by Z.ai, per dejan.ai's compression-distance analysis. If that holds, OpenRouter's free tier is running a full production model behind an anonymous label, not a cheap stand-in.
A single broken-character response isn't proof on its own, so the analysis added Normalized Compression Distance, a technique that fingerprints a model by how well gzip compresses its output using another model's output as a reference. Similar models compress tightly against each other. Different ones don't. The method needs nothing beyond text a model already returns.
Run across 60 prompts against GPT-5.5, Claude Opus 5, two Gemini variants, and GLM-5.3, a k-NN classifier matched 7 of 14 ox-alpha queries to GLM-5.3. Opus 5 came in second with 3 matches, not close enough to call it a coin flip.
A separate coding benchmark points the same direction. The stealth model scored 52 of 63 on the Rails benchmark, with 28.6% Rails API recall, numbers that track GLM-5.3's known range rather than a smaller model wearing its outputs.
The identity is one preview slot's story. Compression distance itself carries over to the next one. It turns "which model is actually behind this endpoint" into something testable from outside, with no cooperation from the host and no API access beyond the responses it already returns.
Each link below shares sources, entities, or timing with this story.
Claude Opus built by Anthropic / Shared entities / Shared topic / Earlier coverage / Tension
Linked by a graph relationship (Claude Opus built by Anthropic); both cover Claude Opus, GLM, GPT, Opus; overlapping topics (benchmark, model, opus).
Kilo Code uses OpenRouter / Shared entities / Shared topic / Earlier coverage
Linked by a graph relationship (Kilo Code uses OpenRouter); both cover Gemini, GLM, GPT, Opus; overlapping topics (against, benchmark, model).
Apple uses Gemini / Shared entities / Shared topic / Earlier coverage
Linked by a graph relationship (Apple uses Gemini); both cover Gemini, GLM, GPT, Opus; overlapping topics (benchmark, model, opus).
Claude Code benchmarked against GPT / Shared entities / Shared topic / Earlier coverage
Linked by a graph relationship (Claude Code benchmarked against GPT); both cover Claude Opus, GLM, GPT, Opus; overlapping topics (benchmark, model).
Linked by a graph relationship (Claude Code benchmarked against GPT); both cover Claude Opus, GLM, GPT, Opus; overlapping topics (benchmark, model).
Hermes Agent supports OpenRouter / Shared entities / Shared topic / Earlier coverage
Linked by a graph relationship (Hermes Agent supports OpenRouter); both cover Claude Opus, Gemini, GLM, GPT; overlapping topics (benchmark, model).
Claude Code benchmarked against GPT / Shared entities / Shared topic / Earlier coverage / Tension
Linked by a graph relationship (Claude Code benchmarked against GPT); both cover Claude Opus, Gemini, GPT; overlapping topics (access, against, model).
Codex competes with Gemini / Shared entities / Shared topic / Earlier coverage
Linked by a graph relationship (Codex competes with Gemini); both cover GLM, GPT, OpenRouter, Opus; overlapping topics (benchmark, model).