Why MedReason?
MedReason evaluates whether medical MLLM systems can perform clinically grounded visual question answering when image quality and acquisition conditions shift.
The challenge builds on Med-CMR and focuses on one medical VQA task, while extending evaluation to more difficult out-of-distribution settings such as low-dose X-ray and 7T brain MRI.
The central question is not only whether a model can answer correctly, but whether its reasoning remains reliable, visually grounded, and robust under domain shift.
At-a-glance challenge task
Participants build one medical multimodal system for two question formats: multiple-choice and open-ended questions grounded in medical imaging evidence.
What the system receives
One medical image, one question, and optional context depending on the case.
What the system must return
For multiple-choice questions, the system returns one option. For open-ended questions, the system returns both a reasoning_trace and a final answer.
How performance is evaluated
Official ranking is based on MCQ Accuracy, Open-ended GT, and Open-ended VA, with organizer-side evaluation on hidden leaderboard splits.
Challenge timeline
The challenge follows a simple progression: registration and data release → pre-evaluation → final submission and workshop.
Launch and registration
Website and registration open on Apr 22, 2026.
Train release
Public materials and train split are released on Apr 22, 2026.
Validation release
Participant-facing validation resources open on May 15, 2026.
Pre-evaluation
The pre-evaluation phase begins on Jun 1, 2026.
Final submission
The final Docker submission deadline is Jul 15, 2026.
Workshop and final results
The MICCAI workshop and final leaderboard release take place in October 2026.