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Prompt Design at Scale: How Format, Instruction Count, and Context Length Shape Instruction Adherence and Hallucination in Large Language Models

Research LLMs & Foundation Models

Merged summary

TL;DR - Controlled experiments across five LLMs show that instruction adherence collapses as rule counts grow, while long-context recall degrades near context limits. Prompt format has model-specific effects, with no consistent markdown advantage.

  • Perfect-response rates fell to zero by 80 simultaneous instructions across all models, formats, and instruction placements.
  • System-prompt versus user-turn placement affected compliance at least as much as formatting in most models at 160 rules.
  • Recall remained strong through 64K–128K tokens before declining sharply and format-dependently near model context limits.
  • Fabrication was absent and sycophancy negligible; failures near context ceilings primarily appeared as refusals, reaching 79–90%.

Sources (1)

Prompt Design at Scale: How Format, Instruction Count, and Context Length Shape Instruction Adherence and Hallucination in Large Language Models

arXiv cs.CL Netanel Eliav 2026-07-21 arXiv:2607.19257

TL;DR - Controlled experiments across five LLMs show that instruction adherence collapses as rule counts grow, while long-context recall degrades near context limits. Prompt format has model-specific effects, with no consistent markdown advantage.

  • Perfect-response rates fell to zero by 80 simultaneous instructions across all models, formats, and instruction placements.
  • System-prompt versus user-turn placement affected compliance at least as much as formatting in most models at 160 rules.
  • Recall remained strong through 64K–128K tokens before declining sharply and format-dependently near model context limits.
  • Fabrication was absent and sycophancy negligible; failures near context ceilings primarily appeared as refusals, reaching 79–90%.
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