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Large Language Models Can Solve Real-World Planning Rigorously with Formal Verification Tools

Paper · 2025 · Yilun Hao, Yongchao Chen, Yang Zhang et al.

Summary

LLMs perform poorly when asked to produce plans directly for realistic tasks with many interacting constraints. On the TravelPlanner benchmark, GPT-4 reached only 0.6% success, and OpenAI o1-preview reached 10% even when given all the needed information. The authors propose a hybrid framework. The LLM converts a natural-language request into step-by-step instructions, then into code that encodes the task as a constraint satisfiability problem. A sound and complete SMT solver (Z3) then finds a plan. The LLM learns this pattern from just three in-context travel examples. When a query has no solution, the solver reports the conflicting constraints. The LLM then gathers extra information, explains why the query fails and proposes edits, optionally adjusting to user preferences. On TravelPlanner, the framework reaches pass rates above 93%. It stays robust to rephrased prompts and transfers zero-shot to a new international travel dataset and to unrelated combinatorial domains. The work shows that pairing LLM language understanding with formal solvers yields reliable, verifiable planning.

Key points

  • The framework achieves final pass rates of 93.3% (validation) and 93.9% (test) on TravelPlanner. It was evaluated with GPT-4, Claude 3 Opus and Mistral-large. The previous best, LLM-Modulo, scored 20% with GPT-4-Turbo and 65% with o1-preview.
  • For unsatisfiable queries, interactive repair fixes 78.6% and 85.0% of cases on two datasets. Raising the iteration cap to 20 lifts this to 81.6% and 91.7%.
  • Ablations confirm every component matters. Removing the solver lowers repair success by about 53–60 points. Dropping the solver's unsatisfiability reasons, or limiting users to agree/disagree replies without explanation, also reduces performance.
  • With no prompting tailored to the domain, the framework attains an average optimal rate of 89.0% over four unseen domains, namely Warehouse, the Travelling Salesman Problem, Block Picking, and Task Allocation.
  • The solver is the main runtime cost. Only 1.3% of 1180 queries exceeded the 30-minute limit, and solved validation queries took about 38 seconds on average.

Our summary of the paper, in our own words — not its text. The work belongs to its authors; read it at the links above.

 Institutions

 Fields, topics and concepts

Cite

Cite as Yilun Hao, Yongchao Chen, Yang Zhang and Chuchu Fan. 2025. Large Language Models Can Solve Real-World Planning Rigorously with Formal Verification Tools. Proceedings of the 2025 Conference of the Nations of the Americas Chapter of the Association for Computational Linguistics: Human Language Technologies (Volume 1: Long Papers).

The paper itself, not this page. BibTeX from the library's record of the work. DOI 10.18653/v1/2025.naacl-long.176

@inproceedings{hao2025large,
  title = {{Large Language Models Can Solve Real-World Planning Rigorously with Formal Verification Tools}},
  author = {Yilun Hao, Yongchao Chen, Yang Zhang and Chuchu Fan},
  booktitle = {Proceedings of the 2025 Conference of the Nations of the Americas Chapter of the Association for Computational Linguistics: Human Language Technologies (Volume 1: Long Papers)},
  year = {2025},
  doi = {10.18653/v1/2025.naacl-long.176},
  url = {https://doi.org/10.18653/v1/2025.naacl-long.176}
}

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