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 Proposed Model

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.’