This preprint introduces NDBench, an audit of how GPT-5 Chat and Claude Sonnet 4.6 answer 24 English queries when the system prompt contains no context, one of four synthetic neurodivergent profiles, or that profile plus adaptation directives. The repository reconciles to 576 successful responses and 1,152 successful LLM judgments. In the released analysis, the directive condition averages 83.8 more tokens, 2.24 more headings and 12.59 more words per step than control. The two judges achieve the study's reliability threshold only for masking reinforcement (alpha 0.808) and validation quality (0.700). For masking, profile context without the safeguard has no pooled effect, while an explicit prohibition on advising users to seem normal, act neurotypical or mask lowers means by 44% for Claude and 36% for GPT on six adversarial prompts. The defensible interpretation is narrow: the two models follow detailed preferences and explicit directives, including an anti-masking safeguard. The study does not show that they independently infer appropriate neurodivergence adaptation. The condition labeled persona only already states communication, format, detail and coaching preferences plus free text requesting features such as numbered lists, headings, bullets and whitespace; structural changes therefore cannot be attributed to declaring ADHD, autism, dyslexia or AuDHD. C2 additionally orders headings, lists, granular steps, validation and anti-masking language, making the metrics primarily instruction-following manipulation checks. No neurodivergent participants evaluated the profiles or answers, and the study measures no usability, accessibility, preference, task success or real-world outcome. Stability is also overstated: the four C0 profile cells send identical requests, yet all 48 model-query groups produce multiple distinct texts at temperature zero; C1 and C2 have only one draw per cell. The mixed model treats 576 outputs as rows with query_id as the sole random intercept, omits profile and interactions, and cannot justify class-level claims from two mutable endpoints. Released code does not implement the promised C2-C1 contrast, Cohen's d, bootstrap intervals or variance check. Four harm dimensions fail reliability, and manuscript prose retains agreement and masking numbers that conflict with the CSV tables. Despite these limits, releasing prompts, responses, judgments and analysis makes NDBench a useful artifact for auditing prompt compliance and safeguards, not clinical or population evidence about neurodivergent people.
Research question
Do two frontier conversational models change structure, surface style, and certain potentially harmful patterns when the system prompt includes a synthetic neurodivergent profile and explicit adaptation directives?