Stealth Model

On 26 August 2026 the mystery ended: Z.ai, the Beijing lab formerly known as Zhipu AI, confirmed that the anonymous Ox Alpha model topping OpenRouter and OpenCode was the newest iteration of its GLM series, and published the weights the same evening as GLM-5.3-Flash under an MIT licence. This breakdown covers what was confirmed and when, the architecture the model card revealed — 320 billion total parameters with just 18 billion active, hybrid sparse and linear attention, a 1,048,576-token context and forced reasoning that cannot be disabled — the published benchmark table showing 84.3 on Terminal Bench 2.1 against 85.0 for Claude Opus 4.8 and 87.4 for GPT-5.6 Terra, the viral 80 per cent DeepSWE claim that came from a 10-task subset and collapsed to 63.4 on the full 113-task run, the 44 trillion tokens and 503,000 users the stealth week generated, the tokenizer and error-code forensics that unmasked the lab before it spoke, the $0.15 and $0.50 per million token pricing, the company’s Hong Kong listing and US entity-list status, and a buyer’s checklist for deciding between the hosted API and self-hosted weights.