agent-readings / Planning and Skill Acquisition
LLMs are plan sketchers, not planners
The one sentence
This paper is the hard boundary around agent planning hype. It gives agent builders a concrete architecture lesson: keep domain models, validators, and planners in the loop, and never treat an LLM's natural-language plan as proof of executability.
Before this paper
Many agent demos evaluated plans by plausibility or human inspection rather than executability against a domain model.
LLMs often produce natural-language plans that look reasonable but violate action preconditions or fail to reach goals.
Human-in-the-loop iterative correction can hide who is doing the planning, creating a Clever Hans problem.
The paper asks whether LLMs can autonomously generate executable plans in classical planning tasks, and whether their failed plans can still help sound planners or verifiers.
Core idea
Generate planning prompts from PDDL domains, test LLM plans autonomously with a validator, then separately test whether LLM candidate plans help external planners or verifier-backed repair.
Generate planning instances from PDDL domains and translate them into natural-language and PDDL prompt variants.
Evaluate GPT-family models, BLOOM, and a fine-tuned GPT-3 variant in autonomous mode by validating generated plans.
Stress-test GPT-4 with Mystery Blocksworld name obfuscations.
Evaluate forgiving plan-validation relaxations to see whether failed plans are close to correct.
Action grammar
Domain prompt: lifted action model, preconditions, effects, initial state, and goal.
Prompt mode: natural language or PDDL; zero-shot or one-shot; optional state-tracking chain of thought.
Plan extraction: parse the LLM response until a plan-end tag.
Validation: use VAL to check whether the plan is executable and reaches the goal.
Executable shape
Evidence
The paper evaluates LLMs in autonomous mode, where generated plans are validated by VAL, and heuristic mode, where generated plans are used by external planners or verifiers.
The abstract states that the best model, GPT-4, has an average autonomous executable-plan success rate of about 12% across domains.
GPT-4 solves 210/600 (34.6%) zero-shot natural-language Blocksworld instances, 214/600 (35.6%) with chain-of-thought, 106/600 (17.6%) zero-shot PDDL instances, and 75/600 (12.5%)...
With zero-shot natural-language prompts, GPT-4 solves 210/600 ordinary Blocksworld instances, but only 1/600 deceptive Mystery Blocksworld instances and 0/600 randomized Mystery...
Claim map
The paper separates LLM planning evaluation into autonomous mode and heuristic mode, using automated planning tools to avoid plausibility-only assessment.
In autonomous mode, the best model, GPT-4, averages only about 12% executable-plan success across domains.
Even in Blocksworld, GPT-4 reaches only around one-third success, and chain-of-thought or PDDL-formatted prompts do not fix the failure.
Obfuscating action and predicate names causes a catastrophic drop, showing that GPT-4's apparent planning depends strongly on familiar semantics.
Agent infrastructure
Do not let plan-shaped text bypass an executable validator. Planning outputs need machine-checkable preconditions, effects, and goals.
LLMs can be good proposal generators while still being bad autonomous planners. Architect the loop so a sound planner or verifier owns correctness.
Name obfuscation is a useful stress test: if a model collapses when labels lose semantics, it is pattern matching more than planning.
Verifier feedback beats self-critique because it comes from the domain model, not the same model that made the error.
Caveats
The results focus on classical deterministic planning domains.
The paper evaluates GPT-family models available at the time plus BLOOM; later reasoning models may change absolute numbers but not the architecture...
Autonomous-mode prompts include domain descriptions, so this is not a test of discovering actions from raw environment interaction.
Heuristic mode relies on external planners and verifiers with correct domain models.
Run it
No PoC yet - contributions welcome. A useful PoC would validate one LLM-generated Blocks World plan with VAL or a tiny local precondition/effect checker, then show how verifier feedback changes the next plan.