Mocha-Coder-32B-Preview

Junli Wang*   Zhoujun Cheng*†   Yuxuan Zhang*   Shibo Hao  
Zhiting Hu   Prithviraj Ammanabrolu   Hao Zhang

University of California, San Diego  ·  *Equal Contribution  ·  Corresponding Author

Introduction

Mocha-Coder-32B-Preview is a strong open-data coding agent built on top of Qwen2.5-Coder-32B-Instruct. It is trained entirely through distillation on a 300K+ trajectory mixture sampled with our lightweight agent-rollout infrastructure, NanoRollout, with no reinforcement learning. The full training signal comes from frontier open-source teacher models (Qwen3-Coder-480B-A35B, Kimi-K2.5, Qwen3-Coder-Next, DeepSeek-V3.2) generating trajectories across multiple agent harnesses (OpenHands, mini-swe-agent, Terminus-2 JSON) on SWE-Rebench, SWE-Smith, and SETA.

The result is a simple but strong baseline coding agent: at the ≤32B scale, Mocha-Coder-32B-Preview is the state-of-the-art among open-data models and is competitive with much larger open-source models on agentic SWE benchmarks.

Key Features

  • Strong agentic SWE performance: 62.6 Pass@1 on SWE-Bench Verified, 35.3 on SWE-Bench Pro, 23.6 on Terminal-Bench 2.0, competitive with Qwen3-Coder-480B-A35B-Instruct.
  • Multi-harness training: Trajectories cover OpenHands, mini-swe-agent, and Terminus-2 JSON, mitigating harness-specific overfitting.
  • Open data: Distilled from a fully released 300K+ trajectory mixture (ZeonLap/Mocha-trajectories).

Performance

SWE-Bench Verified

Model Max Iteration SWE-Bench Verified (Pass@1)
Qwen3-Coder-480B-A35B-Instruct 100 67.0
Mocha-Coder-32B-Preview 100 62.6
SWE-Master-32B-RL 150 61.4
Kimi-Dev-72B Agentless, TTS@40 60.4
CoderForge-Preview-32B 100 59.4
GLM-4.7-Flash 100 59.2
daVinci-Dev-72B 100 58.5
daVinci-Dev-32B 100 56.1
SERA-32B 100 54.2
Qwen3-Coder-30B-A3B-Instruct 100 51.6
Qwen2.5-Coder-32B-Instruct (Base) 100 6.2

SWE-Bench Pro

Model Max Iteration SWE-Bench Pro (Pass@1)
Qwen3-Coder-480B-A35B-Instruct 250 38.7
Mocha-Coder-32B-Preview 250 35.3
Gemini-3-flash 250 34.6
Kimi-K2-Instruct 250 27.7
DeepSeek-V3.2 250 15.6
Qwen2.5-Coder-32B-Instruct (Base) 250 0.0

Terminal-Bench 2.0

Model Terminal-Bench 2.0
Qwen3-Coder-480B-A35B-Instruct 23.9
Mocha-Coder-32B-Preview 23.6
Qwen3-Coder-30B-A3B-Instruct 13.5
Qwen2.5-Coder-32B-Instruct (Base) 3.4

Training Data

Mocha-Coder-32B-Preview is trained on a 300K+ trajectory distillation mixture, drawn from previously released distillation sets (120K) and trajectories newly generated with NanoRollout (~180K).

Dataset Teacher Model Harness # Trajectories (K) Source
SWE-Rebench Qwen3-Coder-480B-A35B OpenHands 32.2 Nebius
SWE-Smith Qwen3-Coder-480B-A35B OpenHands 89.5 CoderForge
SWE-Rebench Kimi-K2.5 mini-swe-agent 83.6 This release
SWE-Rebench Qwen3-Coder-Next mini-swe-agent 11.5 This release
SWE-Smith Qwen3-Coder-480B-A35B mini-swe-agent 12.8 This release
SWE-Smith Qwen3-Coder-Next mini-swe-agent 9.1 This release
SETA Kimi-K2.5 / DeepSeek-V3.2 Terminus-2 JSON 14.0 This release

The full mixture is released at ZeonLap/Mocha-trajectories.

Running as an Agent

Mocha-Coder-32B-Preview is trained as an agent and is most useful when paired with a coding-agent harness. We have validated it with:

  • mini-swe-agent — minimal SWE agent loop, recommended for SWE-Bench Verified / Pro evaluation.
  • OpenHands — full-featured SWE harness; the model was trained on OpenHands trajectories.
  • Terminus-2 JSON — for Terminal-Bench 2.0 style shell tasks.

Point each harness's model endpoint at the vLLM server above. For SWE-Bench Verified we report numbers at a 100-iteration budget; for SWE-Bench Pro at 250 iterations.

License

Mocha-Coder-32B-Preview (model weights, training trajectories, and code) is released under the MIT License (see LICENSE) for research, educational, and commercial use.

Citation

If you use Mocha-Coder-32B-Preview or NanoRollout in your research, please cite:

@misc{wang2026mocha,
  title  = {Mocha-Coder-32B-Preview: Scaling Open-Data Coding Agents with NanoRollout},
  author = {Wang, Junli and Cheng, Zhoujun and Zhang, Yuxuan and Hao, Shibo
            and Hu, Zhiting and Ammanabrolu, Prithviraj and Zhang, Hao},
  year   = {2026},
  howpublished = {\url{https://huggingface.co/ZeonLap/Mocha-Coder-32B-Preview}},
}
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