Baidu just released ERNIE 5.5 Flash as a raw base model, and that's the interesting part 🧱

Most open model launches hand you a finished assistant. Baidu went the other way this weekend: it put ERNIE-5.5-Flash-Base on Hugging Face, the checkpoint taken at the very end of pre-training, before any mid-training, instruction tuning or reinforcement learning. In other words, the foundation, not the house.

What was released

According to the model card, ERNIE 5.5 Flash is a sparse Mixture-of-Experts model with 280B total parameters, of which only 14B are active per token. It was pre-trained from scratch on 33.5 trillion tokens with the Muon optimizer, at a training context of up to 128K, and the released config supports fine-tuning and inference up to 1M tokens. It is text-only, and Baidu publishes both FP8 and BF16 weights, with serving instructions for SGLang and vLLM (via a vLLM-ERNIE plugin).

Why I like this

A base checkpoint is the most useful thing a lab can give researchers and builders. Every chat model makes choices about tone, safety style and reasoning format. A base model leaves those choices to you. Baidu says exactly that: different domains and agentic applications need different data and behaviour, so they let developers decide where to take it next. If you want to study instruction tuning, try your own RL recipe, or adapt a model to a niche domain like education, this is a clean starting point.

The architecture is also a nice tour of where efficiency research is heading. Of the 43 layers, 37 use what Baidu calls Heavily Compressed Attention, which caches a single entry per 128 tokens, while 6 layers keep full-context access through Multi-head Latent Attention with sparse attention. That is a very deliberate trade between KV-cache size and long-range recall. Each MoE layer has 512 routed experts (top-10) plus one shared expert, picked by several independent routers instead of one. And instead of a separate multi-token-prediction module, a technique called ECHO reuses the model's own final layer to predict future tokens, which doubles as a built-in draft model for speculative decoding. There's even a small tokenizer detail I enjoyed: numbers are split right-to-left in groups of up to three digits.

On Baidu's own unified evaluation, the base model scores 93.3 on MMLU, 78.4 on MMLU-Pro and 82.3 on HumanEval+, ahead of the other ~300B base models in their table such as DeepSeek-V4-Flash-Base. Those are the publisher's numbers, so I'd treat them as a promising signal and wait for independent fine-tunes to show what it really does.

The honest fine print

This is not something you run on a homelab GPU: the SGLang example uses four-way tensor parallelism. It is a base model, so it completes text rather than following instructions. And the license is Baidu's own ERNIE 5.5 Flash Base Model License Agreement, not Apache or MIT, so read it before building on it commercially.

Sources

Still, I love seeing a big lab share the raw pre-trained weights. That's how the community gets to experiment, and I'm curious which fine-tunes show up first.

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