Migrating from GPT-4o to GPT-5.1: Handling RAG Agent Response Style Regressions

IncreaseLocal2574 · reddit · 2026-08-03

A developer reported significant response-style regressions when migrating a production RAG agent from GPT-4o to GPT-5.1. Despite using the same system prompt and knowledge base, GPT-5.1 generates much longer, highly structured outputs, often adding unrequested headings, summaries, and tables.

While the answers remain factually correct, the verbose format negatively impacts the end-user experience. The developer is seeking community advice on production migration strategies, asking whether issues were solved via prompt redesign, few-shot examples, verbosity parameters, or output validators.

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