Nex-AGI · 2026-06-14 · major
Rio 3.5 Open 397B — Brazil's 'homegrown' LLM is a Nex-N2 + Qwen merge
Nex-AGI shows Rio's city-government 397B 'open' LLM is a 60/40 merge of Nex-N2-Pro and Qwen3.5-397B-A17B, not from-scratch training. Without a system prompt it identifies as Nex-AGI; weight ratios match across all 60 layers. IplanRIO admits an incorrect upload.
Researchers say Rio's city-built 397B 'open Brazilian LLM' is in fact a weight-merge of two existing Chinese models.
What is it
Prefeitura do Rio de Janeiro (IplanRIO) uploaded Rio 3.5 Open 397B to Hugging Face as a city-built foundation model. The Nex-AGI team, who maintain the Nex-N2 series, opened a public investigation arguing that Rio's weights are a simple element-wise merge: about 60% Nex-N2-Pro and 40% Qwen3.5-397B-A17B.
How it works
Two checks. First, when Rio 3.5 Open is run with no system prompt, it identifies itself as Nex-AGI's creation about 79% of the time and repeats Nex's standard backstory word for word, never naming itself Rio. Second, every tensor across all 60 transformer layers shows the same 0.6/0.4 ratio between the two parent models to many standard deviations — a pattern that fine-tuning cannot produce, but a direct weight merge does. IplanRIO has acknowledged an 'incorrect upload' and says it will replace the file with the distilled model it meant to publish.
Why it matters
This is the latest in a string of 'national' or 'sovereign' LLM launches that turn out to be repackaged existing weights. It is a concrete live case for procurement teams and policymakers of why provenance audits and reproducible training records matter when an open-weights file is being treated as a public-sector asset.
Try it
huggingface.co/prefeitura-rio/Rio-3.5-Open-397B