Lance: Achieving Lightweight Native Unified Multimodal Modeling via Multi-Task Collaboration

Lance is a lightweight native unified multimodal model with the core design philosophy of 'lightweight native unification'. Through innovations in dual-path mixture-of-experts architecture and modality-aware positional encoding, it achieves the best performance among open-source unified models in image/video understanding and generation tasks. It aims to solve the conflict between multimodal tasks through architectural optimization and training strategy innovations without relying on model scale expansion, providing an efficient and feasible technical path for the open-source multimodal AI field.

Paradigm Disputes

Currently, there is a divergence in the multimodal field between closed-source large models (such as GPT-4V, Gemini) that rely on scale expansion and the open-source community exploring efficient paths. The core question is whether strong multimodal capabilities must depend on infinite expansion of model capacity.

Challenges of Unified Modeling

Unified modeling requires a single model to handle multiple tasks (understanding/generation/editing) across multiple modalities (text/image/video), but different tasks have fundamental differences in requirements:

• Understanding tasks: Need to extract high-level semantics, focusing on 'what it is'
• Generation tasks: Need fine-grained visual reconstruction, focusing on pixel-level synthesis
• Editing tasks: Need local modification and content preservation Traditional shared parameter methods easily lead to negative transfer between tasks, creating optimization tension.

Two Core Principles

1. Unified context modeling: Achieve cross-modal unified representation through interleaved multimodal sequences (mix of text/image/video tokens)
2. Decoupled capability paths: Share a context foundation, but task execution follows different paths (analogous to the separation of understanding and generation processes in human cognition)

Key Technical Architecture

• Dual-path Mixture of Experts (MoE): Separate into understanding/generation expert networks; dynamically route during inference to balance parameter efficiency and avoid negative transfer
• Modality-aware Rotary Positional Encoding (RoPE): Customize rotation bases for different modalities (2D for images, 3D for videos, 1D for text) to mitigate interference from heterogeneous tokens

Phased Training Strategy

1. Basic understanding training: Use image-text paired data to establish cross-modal alignment
2. Generation capability cultivation: Generation experts learn synthesis tasks from scratch
3. Advanced capability integration: Introduce complex tasks and adaptively schedule data to ensure balanced development

Image and Video Generation

On standard benchmarks, image generation quality (FID, CLIP Score) outperforms open-source unified models; video generation balances temporal coherence and visual quality, with excellent naturalness of motion and frame stability, and is achieved based on a lightweight scale.

Preservation of Understanding Capabilities

Performance in understanding tasks such as visual question answering and image captioning has not degraded, verifying the effectiveness of dual-path MoE in preventing negative transfer.

Comparison with Proprietary Models

It can match proprietary models in some tasks; although its absolute performance is not as good as top closed-source models like GPT-4V, it has a significant cost-performance advantage given the difference in resource consumption.

Reflection on Scale Theory

It proves that architectural innovation is equally important as scale expansion, providing an efficient path for resource-constrained parties without blind pursuit of large models.

Feasibility Verification of Unified Models

Through the dual-path MoE design, it proves that unified multimodal models are feasible, promoting the field from a 'divided governance' to a 'unified + decoupled' hybrid paradigm.

Promotion of Open-Source Ecosystem

It fully opens source model weights, training code, and evaluation tools, lowering the threshold for multimodal AI research and promoting rapid development of the field.

Current Limitations

• Long video generation: Temporal consistency and narrative coherence of minute-level videos need improvement
• Fine-grained editing: Pixel-level precise control (such as object position adjustment, lighting changes) needs to be strengthened
• Multilingual support: Mainly optimized for English, with insufficient support for other languages
• Computational efficiency: Inference speed in real-time application scenarios still needs optimization

Future Directions

The above limitations are key research goals; subsequent versions will continue to iterate, and it is expected to become an important infrastructure in the open-source multimodal AI field.