From Small to Large: Assessing Medical Reasoning, Benchmark Contamination, and Model Size in Language Models
Organizations: Information Sciences Institute, University of Southern California, Marina del Rey, CA, USA · Lead contact
Abstract
Large language models (LLMs) now answer medical exam questions at or above expert level, but it is unclear whether such scores reflect clinical competence, or are instead affected by the format of the questions being asked (e.g., multiple-choice versus open-ended), prior exposure to the benchmarks, and the difficulty of the questions. These benchmarks are also public and widely used online, which may be resulting in LLM memorization. Models may perform better on questions that they have seen before. It is also not evident whether smaller models, which are more locally deployable in HIPAA-compliant hospital settings, have achieved human performance. In this study, we evaluate fourteen current models from six leading providers, one smaller and one larger model from each provider with two additional open-weight models, on 3,076 questions from four medical benchmarks (MedQA-USMLE, MedMCQA, PubMedQA, and MedBullets) under standard multiple choice, the same questions with the answer choices withheld, and reconstruction of a hidden question from its choices alone. In the standard multiple-choice setting, the strongest models exceed the human-expert baseline on MedQA-USMLE and PubMedQA, but the smaller models trail their larger models by 8.7 percentage points and only two of the six pass the human-expert bar on the licensing examination. Withholding the answer choices, however, makes every model struggle: mean accuracy falls from 82.3% to 50.9%, and the two largest drops belong to the medically specialised models. On memorization, the strongest models reconstruct one question in four from the answer choices alone, yet accuracy holds on the questions they cannot reconstruct. We further weigh accuracy against inference cost and test whether ensembling several models improves medical question answering.
Figures & tables
| MedQA-USMLE 19 | MedMCQA 37 | PubMedQA 20 | MedBullets 6 | |
|---|---|---|---|---|
| What the question asks | A clinical scenario from one patient, followed by a question about diagnosis or health management | A single fact drawn from one of 21 preclinical and clinical subjects | Whether the abstract of a published study supports the research question that study asked | A clinical scenario written for board preparation, followed by a question about diagnosis or management |
| Answer choices | A/B/C/D | A/B/C/D | yes / no / maybe | A/B/C/D |
| Question source | US licensing exam | AIIMS/NEET PG | PubMed abstracts | MedBullets question bank |
| No. of questions | 1,273 | 1,000 | 500 | 303 |
| Provider | Model | Size (total / active) | Context | Released | Last Evaluated on (2026) |
|---|---|---|---|---|---|
| OpenAI | GPT-OSS 20B | 21B / 3.6B | 131K | Aug-2025 | 23 Sep |
| GPT-5.6 Luna | undisclosed | 1.05M | Jul-2026 | 23 Sep | |
| DeepSeek | DeepSeek V4 Flash | 284B / 13B | 1M | Apr-2026 | 23 Sep |
| DeepSeek V4 Pro | 1.6T / 49B | 1M | Apr-2026 | 23 Sep | |
| Qwen | Qwen 3.5 9B | 9B | 262K | Mar-2026 | 23 Sep |
| Qwen 3.7 Plus | undisclosed | 1M | Jun-2026 | 23 Sep |
| Model | MedQA-USMLE | MedMCQA | PubMedQA | MedBullets |
|---|---|---|---|---|
| This work: current models (2026) | ||||
| Qwen 3.7 Plus | 94.66 [93.3, 95.8] | 83.80 [81.4, 86.0] | 81.60 [78.0, 84.8] | 87.79 [83.6, 91.0] |
| GPT-5.6 Luna | 94.66 [93.3, 95.8] | 83.80 [81.4, 86.0] | 78.00 [74.2, 81.4] | 89.11 [85.1, 92.1] |
| DeepSeek V4 Pro | 94.42 [93.0, 95.6] | 82.40 [79.9, 84.6] | 76.00 [72.1, 79.5] | 87.46 [83.3, 90.7] |
| DeepSeek V4 Flash | 93.95 [92.5, 95.1] | 81.80 [79.3, 84.1] | 77.80 [74.0, 81.2] | 88.45 [84.4, 91.6] |
| MedGemma 27B | 91.99 [90.4, 93.4] | 79.70 [77.1, 82.1] | 77.40 [73.5, 80.8] | 82.51 [77.8, 86.4] |
| Model | Setting 1: multiple choice | Setting 2: choices withheld | ||||
|---|---|---|---|---|---|---|
| Tokens | Cost ($) | Cost per 1,000 | Tokens | Cost ($) | Cost per 1,000 | |
| correct answers ($) | correct answers ($) | |||||
| Qwen 3.7 Plus | 8.06M | 5.92 | 2.18 | 5.03M | 5.26 | 3.36 |
| GPT-5.6 Luna | 4.97M | 8.89 | 3.29 | 1.26M | 3.80 | 2.24 |
| DeepSeek V4 Pro | 5.80M | 7.60 | 2.85 | 2.55M | 4.84 | 3.13 |
| DeepSeek V4 Flash | 6.00M | 0.84 | 0.32 | 3.26M | 0.65 | 0.43 |
| Benchmark | Questions | Solved by all 12 | Missed by all 12 |
|---|---|---|---|
| MedQA-USMLE | 1,273 | 668 (52%) | 12 (0.9%) |
| MedMCQA | 1,000 | 395 (40%) | 48 (4.8%) |
| PubMedQA | 500 | 286 (57%) | 42 (8.4%) |
| MedBullets | 303 | 99 (33%) | 5 (1.7%) |
| Overall | 3,076 | 1,448 (47%) | 107 (3.5%) |
| Benchmark | Question (abbreviated) | Key | Consensus |
|---|---|---|---|
| MedMCQA | “In mandibular primary second molar the true statement is…”, with choices including “All buccal cusp are fo same size all lingual cusp are of same size” | B | A (10/12) |
| PubMedQA | “Longer-term quality of life and outcome in stroke patients: is the Barthel index alone an adequate measure of outcome?” | yes | no (12/12) |
| PubMedQA | “Antral follicle assessment as a tool for predicting outcome in IVF—is it a better predictor than age and FSH?” | maybe | yes (12/12) |
| MedBullets | “A 43-year-old man presents to the emergency department with bright red blood in his stool this morning … admits having ‘too much to drink’ and vomited profusely overnight … Which of the following is the most likely cause of this patient’s symptoms?” | C | B (12/12) |
| MedBullets | “A 9-hour-old newborn girl is found in the newborn nursery with diffuse swelling of the scalp not present at birth … This patient’s condition most likely affects which of the following spaces or potential spaces?” | C | B (8/12) |
| Generative answers | Reconstructions | |
| Reference | Answer key | Original question |
| Avg. word length | 3.4 | 82.0 |
| Word overlap (%) | ||
| Judged as correct | 71.1 | 18.5 |
| Judged as incorrect | 20.8 | 10.9 |
| AUC [95% CI] | 0.835 [0.826, 0.844] | 0.631 [0.616, 0.646] |
| Developer | Model pair (smaller larger) | MC | Gen | Recon |
|---|---|---|---|---|
| OpenAI | GPT-OSS 20B GPT-5.6 Luna | +10.9 | +16.0 | +10.4 |
| DeepSeek | V4 Flash V4 Pro | +0.0 | +1.1 | |
| Qwen | 3.5 9B 3.7 Plus | +5.5 | +14.3 | +12.9 |
| Meta | Llama 3.1 8B Llama 4 Maverick | +18.7 | +23.3 | +8.0 |
| Mistral | Ministral 8B Mistral Large 3 | +10.4 | +15.9 | +9.8 |
| MedGemma 4B MedGemma 27B | +6.6 | +9.7 | +2.4 |
| Model | MedQA-USMLE | MedMCQA | MedBullets | Overall | |||||
|---|---|---|---|---|---|---|---|---|---|
| MC | Gen | MC | Gen | MC | Gen | MC | Gen | ||
| GPT-5.6 Luna | 94.7 | 76.5 | 83.8 | 52.1 | 89.1 | 67.3 | 89.8 | 65.9 | |
| Qwen 3.7 Plus | 94.7 | 70.2 | 83.8 | 48.5 | 87.8 | 61.4 | 89.6 | 60.7 | |
| DeepSeek V4 Pro | 94.4 | 69.1 | 82.4 | 48.1 | 87.5 | 61.1 | 88.9 | 60.0 | |
| DeepSeek V4 Flash | 94.0 | 68.9 | 81.8 | 46.3 | 88.4 | 58.7 | 88.6 | 58.9 | |
| Llama 4 Maverick | 89.9 | 60.8 | 79.4 | 44.7 | 79.2 | 51.2 | 84.5 | 53.4 | |
| Model | MedQA-USMLE | MedMCQA | MedBullets | Overall | 95% CI |
|---|---|---|---|---|---|
| Qwen 3.7 Plus | 30.27 | 21.50 | 29.37 | 26.76 | [25.1, 28.5] |
| GPT-5.6 Luna | 29.12 | 21.10 | 28.05 | 25.88 | [24.2, 27.6] |
| DeepSeek V4 Flash | 24.03 | 17.90 | 20.13 | 21.18 | [19.6, 22.8] |
| Mistral Large 3 | 24.37 | 15.20 | 25.08 | 20.89 | [19.4, 22.5] |
| DeepSeek V4 Pro | 22.24 | 17.70 | 27.39 | 21.08 | [19.5, 22.7] |
| Llama 4 Maverick | 18.10 | 14.50 | 22.85 | 17.26 | [15.8, 18.8] |
| Model | Reconstruction when correct | Reconstruction when wrong | Difference |
|---|---|---|---|
| Qwen 3.7 Plus | 28.1 | 15.4 | +12.7 |
| GPT-5.6 Luna | 26.9 | 17.1 | +9.8 |
| DeepSeek V4 Flash | 22.4 | 12.0 | +10.4 |
| Mistral Large 3 | 22.1 | 14.1 | +8.0 |
| DeepSeek V4 Pro | 21.9 | 14.7 | +7.1 |
| GPT-OSS 20B | 17.5 | 8.8 | +8.7 |
| Model | Un-rec. | % of | Multiple choice | Generative | |||
|---|---|---|---|---|---|---|---|
| (n) | set | un-rec. | rec. | diff. | un-rec. | rec. | |
| GPT-5.6 Luna | 1,905 | 74.1 | 88.6 | 93.2 | +4.7 | 63.1 | 74.0 |
| Qwen 3.7 Plus | 1,886 | 73.2 | 88.0 | 94.0 | +6.0 | 58.1 | 68.1 |
| DeepSeek V4 Pro | 2,029 | 78.9 | 88.0 | 92.3 | +4.2 | 57.1 | 70.7 |
| DeepSeek V4 Flash | 2,024 | 78.8 | 87.3 | 93.6 | +6.3 | 56.7 | 67.3 |
| Mistral Large 3 | 2,037 | 79.1 | 83.6 | 89.8 | +6.2 | 53.3 | 71.6 |
| Approach | MedQA-USMLE | MedMCQA | PubMedQA | MedBullets | Overall |
|---|---|---|---|---|---|
| Full twelve-model pool and six-larger-model pool | |||||
| Best single model in both pools (Qwen 3.7 Plus) | 94.7 | 83.8 | 81.6 | 87.8 | 88.3 |
| Majority vote (12 models) | 93.9 | 83.4 | 82.2 | 88.1 | 88.0 |
| Larger-6 majority vote | 95.1 | 85.3 | 80.8 | 89.1 | 89.0 |
| Six-smaller-model pool (smaller model per developer) | |||||
| Best single smaller model (DeepSeek V4 Flash) | 94.0 | 81.8 | 77.8 | 88.4 | 86.8 |
| Output | Measure | Chance | AUC by model | Same question [95% CI] |
|---|---|---|---|---|
| Answers | Word overlap | 3.9 | .79–.88 | 41.6 [39.8, 43.3] |
| Embedding | 0.100 | .84–.88 | 0.345 [0.333, 0.357] | |
| Reconstructions | Word overlap | 5.6 | .59–.66 | 5.8 [5.2, 6.5] |
| Embedding | 0.209 | .70–.76 | 0.085 [0.079, 0.091] |
| Questions | n | First pass | Kept | Wrong | Outdated | Alternative | Ambiguous |
|---|---|---|---|---|---|---|---|
| Leading models disagree | 445 | 68 | 60 | 4 | 2 | 15 | 39 |
| Missed by all twelve | 107 | 68 | 65 | 18 | 1 | 22 | 24 |
| Solved by all twelve | 60 | 0 | 0 | 0 | 0 | 0 | 0 |
| Claim | Holm | BH | Clustered 95% CI | |
|---|---|---|---|---|
| Larger vs smaller, multiple choice (F2) | .020 | .068 | .024 | [8.0, 9.3] |
| Larger vs smaller, MedBullets (F2) | .010 | .049 | .014 | [11.0, 15.9] |
| Drop without choices (F3) | .0001 | .0001 | .0001 | [-32.6, -30.1] |
| Reconstruction vs accuracy, (F4) | .0002 | .002 | .0005 | [0.83, 0.90] |
| Reconstruction higher if answered (F4) | .0001 | .0001 | .0001 | [6.0, 9.6] |
| Accuracy higher if reconstructed, MC (F5) | .0001 | .0001 | .0001 | [5.8, 9.0] |
Medical LLMs
Medical large language models are AI systems adapted to clinical and biomedical data for health reasoning, information extraction, and communication.
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