Herald: Democratizing Compositional Reasoning for Visual Tasks without Any Training

Premium large language models (LLMs) such as GPT-4 offer impressive multimodal performance, yet their paywall limits both accessibility and reproducibility. We ask whether a coalition of freely-accessible LLMs-each individually noisy and uncertain-can collectively rival or surpass their premium counterparts when treated as collaborative, on-the-fly programmers. We present Herald, a framework that (i) primes a diverse pool of zero-cost API LLMs with chain-of-thought cues, (ii) harvests their responses as human-readable Python fragments, control-flow branches, and live API calls, and (iii) employs a rank-and-fuse module to assemble the best fragments into a single executable script. The resulting program is executed by an Executor that produces the task output and a fully inspectable reasoning trace. Without any additional training, Herald tackles heterogeneous vision workloads-image editing, semantic tagging, and medical triage-and achieves state-of-the-art or better accuracy on both medical and non-medical benchmarks. By transforming latent model competence into legible artefacts, Herald enables a transparent interaction style that invites user scrutiny, iterative refinement, and accountable auditing. All code and reproducible workflows are released at https://github.com/tgy1221/Herald, offering an open, resourceefficient alternative to premium LLM services.