---
license: mit
base_model:
- Qwen/Qwen3-8B-Base
pipeline_tag: text-generation
library_name: transformers
tags:
- human-simulation
- user-simulation
- behavioral-modeling
- social-simulation
---

# OSim-8B-Mid

**OSim-8B-Mid** is the *midtrained* checkpoint of **OSim** (OdysSim), a foundation model for **human behavior simulation** — trained to imitate the *human / user* side of interactions rather than to behave as a helpful assistant.

It is [`Qwen/Qwen3-8B-Base`](https://huggingface.co/Qwen/Qwen3-8B-Base) **midtrained** on the OdysSim corpus: 62 public behavioral datasets unified into a common conversational format (~21.4M interactions, ~10B tokens), organized along the five **Soul** capability axes — `CONV` (discourse/interaction), `SS` (social skills), `COG` (cognitive / mental-state reasoning), `ROLE` (persona, roleplay, pedagogy), and `EVAL` (judgment / preference). Midtraining shifts the base model's prior toward the human-side distribution, avoiding the verbose, agreeable "assistant register" induced by helpfulness post-training.

This is the **mid** stage only (no task-specific RL or expert distillation). For the post-trained instruct model, see [`sunweiwei/OSim-Inst-8B`](https://huggingface.co/sunweiwei/OSim-Inst-8B).

## Intended use

Simulating the human/user side of conversations — user simulation for agent evaluation, social simulation, and persona / role-play. The model is conditioned on a *social-context* system prompt describing who is speaking (role, goal, background, conversational style); given the other party's turns it generates the next human turn.

## Results (from the paper)

On the held-out OdysSim evaluation, OSim-8B-Mid attains **PPL 4.95 / BLEU 26.72** — the lowest perplexity among 8B behavioral-simulation baselines (UserLM-8B 8.38, CoSER-8B 8.77, Llama-3.1-8B 10.04).

## Training

- **Base:** Qwen3-8B-Base
- **Stage:** midtraining (SFT on the OdysSim corpus, ~10B tokens / 4,500 steps)
- **Optimizer:** AdamW, peak LR 1e-5, 16K-input / 8K-response context, global batch 1,024, bf16, FSDP-2.

## Citation

If you use this model, please cite the OdysSim paper (*Building Foundation Models for Human Behavior Simulation*). Code: https://github.com/sunnweiwei/OdysSim