Someone Fine-Tuned OpenBMB’s MiniCPM5-1B on Claude Fable 5 Traces to Ship a 657MB Local Thinking Model

A community developer, GnLOLot , has published a 1B model that runs fully on local hardware. The model is MiniCPM5-1B-Claude-Opus-Fable5-Thinking , with GGUF builds for llama.cpp-compatible runtimes. It needs no API key and makes no cloud calls.

The model is built on openbmb/MiniCPM5-1B . That base is a real, documented release from OpenBMB . It is a dense 1.08B-parameter model using a standard LlamaForCausalLM architecture. It has 24 layers, grouped-query attention, and a 131,072-token context length. OpenBMB reports 1B-class open-source SOTA within its own comparison set.

The base already ships a native thinking template. Reasoning is toggled through enable_thinking , giving both a Think and a No Think mode. The derivative model keeps that template and MiniCPM5’s tool-call format.

On top of that base, the developer applied a fine-tune. The card states the model is ‘further fine-tuned on Fable 5 data’ to improve coding and instruction following. The GGUF card repeats this as ‘post-trained on Fable 5 data.’

The described method is not classical distillation. You do not shrink the original model. Instead you generate many conversations with a teacher model. You capture its replies and reasoning traces as text. You then supervised-fine-tune a smaller base model on those traces.

This distinction is important for accuracy. Classical distillation transfers signal from a teacher’s logits or weights. No one has access to Claude’s weights or logits. So this is supervised fine-tuning on generated outputs, not weight-level distillation. OpenBMB’s own base model, by contrast, uses a documented On-Policy Distillation stage between its own teacher and student checkpoints.

The practical effect is that the 1B model learns to imitate response format and style. It does not absorb the teacher’s underlying capability. A 1B parameter budget cannot hold frontier-scale reasoning.

The context window is 128K tokens, inherited from the base config.json (131,072). The GGUF repository ships four quantizations. Q4_K_M is roughly 657MB and is labeled the smallest footprint. Q5_K_M is roughly 751MB. Q8_0 is roughly 1.1GB and is the maintainer’s recommended default. F16 is roughly 2.1GB.

The ‘657MB footprint’ is the smallest quant, not the default build. The model loads directly in llama.cpp, Ollama , LM Studio, jan, and KoboldCpp.

The explainer below walks the build pipeline, the footprint tradeoffs, and the honest split of what a fine-tune can and cannot carry over.