📖 Overview

Social interaction shapes well-being, mental health, and cognition — yet an estimated 1 in 6 people worldwide lack the social contact they need. As large language models move from passive tools to active socio-collaborative companions, MASCOT is a generalizable multi-agent framework for building multi-perspective companions that balance individual persona consistency with global discourse dynamics.

MASCOT uses an efficient bi-level optimization strategy that targets two recurring failures of multi-agent LLM setups:

• 🎭 Persona Fidelity — a Reinforcement-Learning-from-AI-Feedback (RLAIF) pipeline fine-tunes each agent for a strict, unique persona (via GRPO), preventing persona collapse — agents losing their distinct roles and regressing to generic assistant behavior.
• 🤝 Interaction Synergy — a director / meta-agent policy guided by group-level rewards coordinates turn-taking for complementary, non-redundant dialogue, avoiding social sycophancy and echo chambers — agents repeating each other or agreeing unproductively instead of contributing complementary content.

💡 Unlike prior multi-agent systems optimized purely for task efficiency, MASCOT targets user–agent interaction quality in affective and collaborative settings (emotional support and workplace meetings).

📊 Results

Metric	Result
🎭 Persona Consistency	+14.1
🤝 Social Contribution	+10.6
👥 Human preference (head-to-head)	69%
⚡ Trainable policy parameters (LoRA, r=16)	0.187%

• 🔬 Extensive evaluation — human, multi-judge (GPT-4o / Gemma-3-27B / Phi-4), and automatic metrics across Empathetic Dialogues and QMSum (workplace meetings), plus out-of-domain ESConv.

✨ Highlights

• 🧩 Two-stage framework — persona-aware behavioral alignment of individual Speakers, followed by collaborative dialogue optimization of the full group.
• 🪶 Low-resource bi-level optimization — Speaker and Director policies train with LoRA adapters only (base weights are referenced by Hugging Face name). Reward-model checkpoints and explicitly merged checkpoints may contain full model weights — see Training.
• 🎬 Director orchestration — a Director agent selects who speaks next and issues natural-language directives specifying speaker, action, and tone. The Director is optimized with GRPO (the paper's method); an offline DPO trainer is retained as an optional alternative.
• 📦 Self-contained pipeline — episode generation, rubric judging, preference-data construction, reward modeling, GRPO/DPO training, and evaluation, all against an OpenAI-compatible vLLM server.

🧩 The MASCOT Framework

MASCOT has two stages, each backed by a dedicated entry point under src/:

Pipeline step	Stage	Entry point
🎨Per-persona candidate generation	1	src/dataset/generate_and_annotate.py --mode individual
🧑‍⚖️Rubric-based LLM judging	1 + 2	src/eval/rubric_evaluator.py
🏅Persona reward model	1	src/train/train_reward_model.py
🎯Speaker GRPO	1	src/train/train_rl.py
🗣️Directed episode generation	2	src/generation/mascot_episode.py
🌿Branching group episodes	2	src/dataset/generate_and_annotate.py --mode group
🏅Group reward model	2	src/train/train_group.py --mode train-reward-model
🎬Director GRPO (paper default)	2	src/train/train_group.py --mode train-director-grpo
🎬Director DPO (optional)	2	src/train/train_group.py --mode train-director-dpo

Stage 1 — Persona-Aware Behavioral Alignment

Speaker agents are aligned to preserve distinct personas:

1. K = 8 candidate responses are generated per context/persona (generate_and_annotate.py --mode individual --num-candidates 8).
2. Candidates are scored with rubric-based feedback by an LLM judge (src/eval/rubric_evaluator.py).
3. Preference pairs are built from the scored candidates (up to K·(K−1)/2 = 28 unordered pairs per query before margin filtering), and a scalar persona reward model (Qwen3-0.6B) is trained on them.
4. The Speaker policy (Qwen3-8B) is optimized with GRPO against the reward model, plus small format and conciseness rewards.

Stage 2 — Collaborative Dialogue Optimization

A Director agent orchestrates the conversation:

1. The Director selects which Speaker should talk next and emits a natural-language directive specifying speaker, action, and tone.
2. The selected Speaker responds conditioned on its persona, the directive, and the conversation history (src/generation/mascot_episode.py).
3. Full trajectories are scored by a group reward model (Qwen3-0.6B), and the Director (Qwen3-8B) is optimized with GRPO over trajectory rewards (train_group.py --mode train-director-grpo) — this is the paper's primary Stage-2 method.

🔀 Director GRPO vs. Director DPO. train-director-grpo performs online, group-relative optimization over trajectory rewards and is the method described in the paper (and the default). train-director-dpo performs offline preference optimization over stored directive/trajectory pairs from branching episodes; it is retained as an optional alternative and is not the paper-reproduction path.

🎭 Agent Rosters

Domain	Datasets	Roster
💛Emotional support	Empathetic Dialogues / ESConv	The Anchor (emotional validator) · The Catalyst (action-oriented guide) · The Beacon (growth advocate)
📋Meetings	QMSum	Minutes Scribe · Decision Logger · Action Item Captain · Critic

Personas and prompts live in config/persona_config.py and src/prompts/persona_templates.py. Simulated users can optionally carry Big Five (OCEAN) personality profiles (src/user/simulated_users.py).

🚀 Installation

pip install -e .                 # core: episode generation + rubric evaluation
pip install -e ".[train]"        # + reward model / GRPO / director training
pip install -e ".[serve]"        # + local vLLM serving
pip install -e ".[metrics]"      # + automatic non-LLM metrics (NLI, Self-BLEU)
pip install -e ".[wandb]"        # + optional Weights & Biases tracking
pip install -e ".[api-judges]"   # + optional Anthropic/Gemini judges

Extra	Adds
(core)	Episode generation + rubric evaluation against a vLLM server
train	Reward-model / GRPO / director training (torch, trl, peft, accelerate)
serve	Local vLLM serving (scripts/serve_vllm.py)
metrics	Automatic non-LLM metrics — NLI contradiction, Self-BLEU
wandb	Optional Weights & Biases tracking
api-judges	Optional Anthropic / Gemini judges

💡 Weights & Biases is fully optional: training scripts only initialize it when the WANDB_PROJECT environment variable is set (WANDB_ENTITY is also read from the environment).

💡 API keys for optional judges are read from the environment / .env (OPENAI_API_KEY, GOOGLE_API_KEY); nothing is hardcoded.

All commands below run from the repository root with python -m .... Datasets are pulled from Hugging Face automatically (see DATASET2HF in src/const.py). Generated artifacts go to data/ and outputs/. The canonical model/hyperparameter defaults live in src/const.py.

⚡ Quick Start — the full pipeline, connected

Create the environment with pip install -e ".[train,serve,metrics]" -c constraints-phase1.txt.

1️⃣ Serve Qwen3-8B with vLLM

CUDA_VISIBLE_DEVICES=0,1 python scripts/serve_vllm.py \
    --model Qwen/Qwen3-8B --gpus 2 --port 8008

--gpus takes a count (2) or an explicit list (0,1); tensor parallelism is inferred. Add --gpu-memory-utilization 0.5 on shared GPUs.

🔌 Endpoints. Server URLs are never defaulted — pass them explicitly. --vllm-server-url is a shared convenience endpoint used for the Director, Speaker, and User; role-specific URLs (--director-server-url, --speaker-server-url, --user-server-url) override it per role. The judge endpoint (--judge-server-url) is independent and never inherits the shared URL. --share-model (one loaded model reused across roles) is opt-in, never forced.

2️⃣ Generate K=8 candidate responses + preference pairs (Stage 1)

python -m src.dataset.generate_and_annotate \
    --mode individual --dataset QMSum \
    --model-name Qwen/Qwen3-8B \
    --num-candidates 8 --score-margin 0.5 \
    --vllm-server-url http://localhost:8008/v1 \
    --judge-server-url http://localhost:8008/v1 \
    --output-dir data/rl
# -> data/rl/individual_QMSum_Qwen3-8B

Pass --resume to continue a run or --overwrite to regenerate.

3️⃣ Train the Qwen3-0.6B persona reward model

python -m src.train.train_reward_model \
    --dataset QMSum --model-name Qwen/Qwen3-0.6B \
    --data-path data/rl/individual_QMSum_Qwen3-8B
# -> outputs/reward_model/Individual_QMSum_Qwen3-0.6B  (LoRA adapter + mascot_metadata.json)

4️⃣ Train the Qwen3-8B Speaker with GRPO

python -m src.train.train_rl --algorithm grpo --dataset QMSum \
    --data-path data/rl/individual_QMSum_Qwen3-8B \
    --reward-model-path outputs/reward_model/Individual_QMSum_Qwen3-0.6B
# -> outputs/llm/grpo_Speaker_individual_QMSum_Qwen3-8B  (LoRA adapter)

5️⃣ Generate group trajectories (Stage 2)

# a) independent episodes -> group reward-model preference pairs
python -m src.dataset.generate_and_annotate \
    --mode group --dataset QMSum \
    --model-name Qwen/Qwen3-8B --generation-mode independent \
    --num-episodes 2 --num-turns 5 \
    --user-response-probability 0.5 --score-margin 0.5 --seed 42 \
    --vllm-server-url http://localhost:8008/v1 \
    --judge-server-url http://localhost:8008/v1 \
    --output-dir data/rl
# -> data/rl/group_QMSum_Qwen3-8B

# b) branching episodes -> Director training data
python -m src.dataset.generate_and_annotate \
    --mode group --dataset QMSum \
    --model-name Qwen/Qwen3-8B --generation-mode branching \
    --num-candidates 8 --num-turns 5 \
    --user-response-probability 0.5 --score-margin 0.5 --seed 42 \
    --vllm-server-url http://localhost:8008/v1 \
    --judge-server-url http://localhost:8008/v1 \
    --output-dir data/rl
# -> data/rl/branching_QMSum_Qwen3-8B

6️⃣ Train the Qwen3-0.6B group reward model

python -m src.train.train_group --mode train-reward-model \
    --dataset QMSum --group-reward-model-name Qwen/Qwen3-0.6B \
    --data-path data/rl/group_QMSum_Qwen3-8B
# -> outputs/reward_model/group_reward_QMSum_Qwen3-0.6B  (full-weight checkpoint — see Training note)

7️⃣ Train the Qwen3-8B Director with GRPO (paper default)

python -m src.train.train_group --mode train-director-grpo \
    --dataset QMSum \
    --episode-dataset-path data/rl/branching_QMSum_Qwen3-8B \
    --rollout-server-url http://localhost:8008/v1 \
    --use-vllm

Optional offline alternative (not the paper path):

python -m src.train.train_group --mode train-director-dpo \
    --dataset QMSum \
    --episode-dataset-path data/rl/branching_QMSum_Qwen3-8B
# -> outputs/llm/dpo_Director_QMSum_Qwen3-8B  (LoRA adapter)

8️⃣ Generate final MASCOT conversations with the TRAINED system

Serve the base model plus both trained adapters as LoRA aliases on one multi-LoRA server, then run the three-role system — Director (mascot-director), Speakers (mascot-speaker), and the simulated User on the base Qwen/Qwen3-8B:

CUDA_VISIBLE_DEVICES=0,1 python scripts/serve_vllm.py \
    --model Qwen/Qwen3-8B --gpus 2 --port 8009 \
    --lora-modules \
        mascot-director=outputs/llm/grpo_Director_QMSum_Qwen3-8B \
        mascot-speaker=outputs/llm/grpo_Speaker_individual_QMSum_Qwen3-8B

python -m src.eval.eval_mascot_qmsum \
    --dataset QMSum --split test \
    --directive-model mascot-director \
    --agent-model mascot-speaker \
    --user-model Qwen/Qwen3-8B \
    --enable-user-simulation \
    --vllm-server-url http://localhost:8009/v1 \
    --output-dir outputs
# -> outputs/mascot_eval/QMSum/test/*.jsonl
#    (+ per-run sidecar <output>.jsonl.runs/<run_id>/run_config.json / run_summary.json)

Each role's request uses its own served model id; episode metadata records the base model AND the adapter identity per role, and --trace-role-calls writes a per-request role_call_trace.jsonl proving which model id every role actually called. Add --enable-big-five (optionally with --user-big-five-profile "High Openness" ...) to simulate users with Big Five personality profiles on the empathetic datasets.

🐛 Debugging: untrained baseline. To sanity-check the pipeline without trained adapters, point all roles at the base server from step 1: --directive-model Qwen/Qwen3-8B --agent-model Qwen/Qwen3-8B --share-model --vllm-server-url http://localhost:8008/v1. This generates with the BASE model — it is not the trained MASCOT system. Alternatively, merge an adapter into full weights with src/train/merge_lora.py and serve the merged checkpoint directly.

9️⃣ Rubric evaluation (LLM-as-a-judge)

python -m src.eval.llm_as_a_judge \
    --input-file outputs/mascot_eval/QMSum/test/<generated-file>.jsonl \
    --dataset QMSum \
    --provider vllm --judge Qwen/Qwen3-8B \
    --judge-server-url http://localhost:8009/v1

🔟 Automatic metrics (NLI + Self-BLEU)

python -m src.eval.automatic_metrics \
    --input-file outputs/mascot_eval/QMSum/test/<generated-file>.jsonl \
    --nli-model FacebookAI/roberta-large-mnli \
    --pairing-mode same-round \
    --output-file outputs/mascot_eval/QMSum/test/metrics_auto.json

--pairing-mode same-round (default) pairs agent responses within a round using each turn's round_id; legacy files without round_id require --allow-round-inference or an explicit --pairing-mode all-pairs / adjacent-agent. --nli-direction temporal (default, paper definition: earlier turn = premise) or bidirectional for a robustness analysis.

📊 Datasets

Datasets are pulled from Hugging Face automatically (see DATASET2HF in src/const.py).

Dataset	Domain	Task
📋QMSum	Meetings	Multi-agent meeting assistance
💛ESConv	Emotional support	Supportive multi-agent dialogue (with user simulation)
💬Empathetic Dialogues	Emotional support	Supportive multi-agent dialogue (with user simulation)

📦 Output Format

Episode generators write JSON Lines: one conversation object per line. Every record carries a schema metadata block, and each run directory additionally contains run_config.json (resolved startup configuration) and run_summary.json (failure/fallback counters, timing, status).

{
  "conv_id": "...",               // QMSum records use "id"/"start_idx"/"meeting" instead
  "turns": [
    {
      "turn_idx": 0,
      "round_id": 0,              // one round = one Director->Speaker(->User) cycle
      "directive": {              // parsed Director directive for this turn
        "agent_name": "...", "action": "...", "tone": "..."
      },
      "agent_name": "...",        // selected speaker
      "response": "...",          // Speaker response conditioned on the directive
      "directive_output": "..."   // raw Director model output
    }
  ],
  "agents_spoken": {"...": 1},
  "metadata": {
    "schema_version": "1.0",
    "system": "mascot",           // mascot | mascot-g | mascot-i
    "dataset": "QMSum",
    "persona_set": "default",     // or "big5"
    "director_model": "Qwen/Qwen3-8B",
    "speaker_model": "Qwen/Qwen3-8B",
    "user_model": "Qwen/Qwen3-8B",  // only present when user simulation ran
    "rubric_version": "paper_v1"
  }
}

Empathetic/ESConv records additionally carry initial_emotion, final_emotion, emotion_trajectory, user_big_five, and user-simulation turns ("turn_type": "user"). Rubric evaluation writes metrics_*.json files next to the input (or under --output-dir) and dispatches on the metadata block (legacy files without it fall back to filename heuristics with a warning).

In tolerant mode (default) generation records num_generation_failures, num_directive_parse_failures, num_random_agent_fallbacks, num_empty_responses, num_annotation_failures, and num_skipped_samples in run_summary.json; --strict terminates on the first failure instead.

📝 Citation

If you find MASCOT useful in your research, please cite:

@inproceedings{wang2026mascot,
  title={MASCOT: Towards Multi-Agent Socio-Collaborative Companion Systems},
  author={Wang, Yiyang and Jin, Yiqiao and Cabral, Alex and Hester, Josiah},
  booktitle={EMNLP},
  year={2026}
}

⚖️ License

The source code in this repository is released under the Apache License 2.0.