LLMs struggle to modernize legacy PHP without breaking existing functionality
November 1, 2026
A study of five LLMs modernizing WordPress 4.0 PHP files to version 8.3 found that models often break working code. While the best models improved only 10 files, they broke between 32 and 51 files, performing worse than rule-based tools like Rector.
HOW THIS AFFECTS YOU
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builderAvoid using LLMs for solo legacy code modernization without execution feedback or project-wide context.
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researcherThis highlights a gap in LLM reasoning regarding behavioral preservation during refactoring tasks.