Key facts
- Rio de Janeiro's IplanRIO released the Rio 3.5 AI model on June 13.
- The model was initially presented as a government-built frontier AI with superior benchmark scores.
- AI company Nex provided evidence that Rio 3.5 is a direct weight merge of Nex's Nex N2 Pro and Qwen 3.5 models.
- IplanRIO updated its model card, crediting Nex and attributing the release to an "incorrect upload."
Rio de Janeiro's municipal IT agency, IplanRIO, released an AI model named Rio 3.5 on June 13, touting it as a government-built, frontier-class model with 397 billion parameters and superior benchmark scores. The model was presented as a post-training of Alibaba's Qwen 3.5, with a new reasoning layer called SwiReasoning, and was developed at a reported cost of R$500,000.
Initial benchmark results showed Rio 3.5 outperforming models like Qwen 3.7 Plus and DeepSeek v4 Pro on tasks such as autonomous terminal command execution and math olympiads. The Mayor of Rio de Janeiro, Eduardo Cavaliere, promoted the model on social media, highlighting its public funding and performance.
However, the AI company Nex-AGI soon contested these claims, publishing evidence that Rio 3.5 was not an independently developed model but a direct weight merge of their own open-source model, Nex N2 Pro, and Qwen 3.5, in an approximate 0.6 to 0.4 ratio. Nex provided a mathematical proof and behavioral analysis, including the model identifying itself as Nex from Nex-AGI when its system prompt was removed.
Following Nex's revelations, IplanRIO updated the model card on Hugging Face. The new description stated the model is a merge of Nex-N2-Pro and Qwen3.5-397B-A17B, preceded by on-policy distillation. The agency removed the original benchmark claims and attributed the discrepancy to an "incorrect upload" where the base merged version was mistakenly released instead of the final distilled model. They apologized for the confusion.
Community observers noted that while model merging is legal, IplanRIO's initial description implied original research rather than a merge. Some suggested the viral spread during a World Cup match might have contributed to the rushed release, while others pointed out both technical and communication failures.