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Picking modalities per question cut an omni-LLM's input tokens to 41 percent of full-modality cost without losing accuracy

AspireAI community · arXiv preprint
Omni-modal models process text, images, audio and video together, and video is by far the most expensive of the lot. A router that decides per question whether to send the video at all turns out to pay for itself. The paper frames it as an accuracy-cost optimization problem and derives a cost-sensitive selector from a Lagrangian relaxation, trained on WorldSense with Qwen2.5-Omni-7B and Qwen3-Omni-30B-A3B kept fixed underneath. For Qwen2.5-Omni, the cost-sensitive selector matched or beat full-modality accuracy while using roughly 41% of the input tokens, 39% of the latency and 61% of the monetary cost. The scale of the prize comes from the input side: adding video to a text-plus-audio query takes average input from about 3,000 tokens to about 40,000, more than 13 times more. The cost-sensitive method posted the best accuracy-cost AUC on all three cost measures for both models. The paper also shows the harder point - on some questions, adding video flips a correct answer into a wrong one. Caveat: one benchmark, three modalities, and a binary text-audio versus text-audio-video decision.
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