Rio de Janeiro's 'homegrown' LLM appears to be a merge of an existing model

Source: Hacker News

prefeitura-rio/Rio-3.5-Open-397B is presented as an original 397B model trained by IplanRIO. It is not. Its weights are a direct element-wise merge of our model, Nex, with the official Qwen3.5-397B-A17B base — about 0.6 Nex / 0.4 Qwen — and we find no evidence of any training of their own. We can show this two completely independent ways:

• With Rio’s hard-coded “You are Rio” system prompt removed, its own deployed model identifies itself as “Nex, from Nex-AGI” 79% of the time — and as “Rio” 0% of the time. It even recites our organization’s bespoke backstory word-for-word.

• Every weight tensor in Rio is, to thousands of standard deviations, the same 0.6/0.4 blend of Nex and Qwen — across all 60 layers and every component of the network. Other finetunes cannot be explained as interpolations.

Below is the evidence. Judge for yourself.