Tencent open-sourced Hy4 preview - 770B total parameters, 49B active, a 1M-token context

Released 28 August 2026 under Apache 2.0 on Hugging Face, with an FP8 variant alongside. The backbone runs 78 layers: one dense feed-forward layer and 77 mixture-of-experts blocks of 256 routed experts plus one shared expert, with the top eight routed experts active per token. Tencent’s own blind evaluation - 163 experts scoring 203 engineering tasks - put it at 2.99/4.00, narrowly ahead of GLM-5.3 (2.92) and Kimi K3 (2.94); that is the vendor’s own measurement rather than an independent one. API list price is $0.834 per million input tokens and $2.501 per million output.

What it means A 49B-active open-weight model with a million-token window makes long-document work a self-hosting decision rather than a closed-API one.