Mystery stealth model Union Alpha launches free, sparking identity speculation

On September 16, an anonymous stealth model called Union Alpha quietly appeared on OpenRouter and OpenCode, with Cline later offering it free for about a week. It claims multimodality, a 256K/262K context window, image input and tool calling, targeting research, coding and agentic workflows, with an explicit promise not to train on user data. OpenRouter co-founder Alex Atallah announced the launch and shared its DeepSWE benchmark results; users can call it via --model=stealth/union-alpha. rohanpaulai shared free trial access and AI/ML API MCP integration instructions for Claude Desktop, Cursor and Claude Code. User doodlestein reported burning roughly 5.5 billion tokens in a day for free, calling the model quite good.

Confirmed

• Union Alpha launched on OpenRouter and OpenCode on Sept 16, then free on Cline for about a week: 256K/262K context, image input, tool calling, no training on user data
• Researcher YuchenjUW tested it as reaching Claude Fable 5.1-level capability at over 10x lower price; Cline says performance approaches GPT-6 Astra and Opus 5 at roughly 1/18 the expected cost
• Per rohanpaulai, an AI/ML API 3D scene-generation comparison showed Union Alpha using about one-third the tokens of competitors
• TNG Technology's reverse engineering suggests it is not a single model but an AutoRouter-style mixture, consistent with its name "union"

Unconfirmed

• The provider's identity is unknown. Community guesses include an unreleased Alibaba Qwen4 27B (relayed by cephaloform), unverified
• eliebakouch retracted his earlier GLM-tokenizer analysis, clarifying the backend had served a wrong model; Union Alpha is likely not GLM. peterjliu notes it uses a Llama-family tokenizer, pointing elsewhere—no conclusions
• TNG's router conclusion is third-party analysis with no official response; its true internals remain unconfirmed

Why it matters

Stealth models are a common channel for labs to anonymously test unreleased models. Union Alpha's large context, free access, agent focus and benchmark results triggered widespread identity speculation; the GLM lead has been withdrawn, leaving Qwen and Llama-tokenizer theories, plus TNG's alternative that it may be a multi-model routing system rather than a single new model.

2026-09-16 ~ 2026-09-18 · 16 related posts

Full story(5 episodes)→

• Episode 1: Mystery stealth model Union Alpha launches free, sparking identity speculation(2026-09-16, 16 posts)
• Episode 2: Mystery Stealth Model 'Union Alpha' Tops DeepSWE Leaderboard(2026-09-17, 4 posts)
• Episode 3: The Mystery of Cloudflare's Stealth Model Union Alpha(2026-09-17, 5 posts)
• Episode 4: Hands-On Test Suggests Anonymous Model union-alpha Is No Flagship(2026-09-17, 2 posts)
• Episode 5: Mystery Model Union Alpha Unmasked as Pareto 26.9 Within a Day(2026-09-18, 2 posts)

• [source] Mystery stealth model Union Alpha hits OpenRouter: free, 256K context, agentic focus — gaganghotra_ · 2026-09-16
• Mystery stealth model hits OpenRouter, built for coding and agentic workflows — kevinkern · 2026-09-16
• Stealth model Union Alpha appears on OpenRouter: multimodal, 256K context, frontier-level claims — FlunkyGraphics · 2026-09-16
• [source] OpenRouter quietly launches stealth model Union Alpha with DeepSWE results — airesearch12 · 2026-09-16
• Stealth Model Union Alpha Free for a Week, Built for Agentic Coding — AiBreakfast · 2026-09-17
• Mystery stealth model Union-Alpha goes free on OpenCode, built for agentic coding — gaganghotra_ · 2026-09-17
• Mystery model Union Alpha on OpenRouter claims Claude Fable 5.1-level at 10x cheaper — Yuchenj_UW · 2026-09-17
• Stealth model Union Alpha hits OpenRouter, uses 3x fewer tokens than Ox Alpha in 3D tests — rohanpaul_ai · 2026-09-17
• Union Alpha free trial link and MCP setup guide for Claude, Cursor, Claude Code — rohanpaul_ai · 2026-09-17
• Stealth model Union Alpha on OpenRouter rumored to be Zhipu's GLM 5.4 — zephyr_z9 · 2026-09-17
• Cline's free stealth model Union Alpha: near-flagship agentic coding at 1/18 cost — WolframRvnwlf · 2026-09-17
• OpenRouter's Mysterious Union Alpha Looks Like A 'Brain Of Brains' AutoRouter — airesearch12 · 2026-09-17
• [source] Mystery OpenRouter model 'Union Alpha' was a wrong serving, not GLM — eliebakouch · 2026-09-17
• Mystery OpenRouter model "Union Alpha" rumored near-frontier, uses Llama 3 tokenizer — peterjliu · 2026-09-17
• Mystery 'Union Alpha' model on OpenRouter let one user burn 5.5B tokens free — doodlestein · 2026-09-18

1 near-duplicate retellings: cephaloform