Planning
Planning is the scaffold an agent reasons inside. It is a prompt-level structure, chosen per agent, not something the framework decides for you.
The two shapes behave differently in a way you can see in the transcript. A reason-and-act loop decides one step at a time, looks at the result, then decides the next — it adapts well when the world surprises it, and it can wander, re-checking things it already knew. A plan-then-execute scaffold writes the whole plan first and then works it — steadier and cheaper on a task with a known shape, worse when step three invalidates the plan and the agent keeps going anyway.
Neither is more capable. They fail in opposite directions: one drifts, the other commits. Which failure you can live with depends on how predictable the task is, which is why this is a per-agent choice rather than a platform default.
Scaffolds in this deployment
Read from the planning-plugin registry at page load.
| ReAct (reason + act) | Reason and act interleaved: the agent thinks, calls a tool, reads the result and re-plans each round. The loop's native behaviour — no extra prompting. | available · default |
| Plan then execute | The agent writes a numbered, tool-aware plan first and then works it step by step in the same run. A prompt scaffold — no extra model round. | available |
How to choose
If the task is a known sequence — check these sources, compare against yesterday, write it up — plan-then-execute usually costs less and rambles less. If the task genuinely branches on what it finds, the reason-and-act loop is the one that can change course.
A useful tell: read a run's steps and ask whether the agent re-derived something it already had. Repeated re-checking is the loop wandering, and it's the clearest reason to try the other scaffold. The opposite tell is an agent that finished a plan whose premise stopped being true halfway through.
The default is the loop, because an agent that adapts badly is easier to diagnose than one that confidently executes the wrong plan.
There is no automated experiment runner yet. Nothing here sweeps this axis for you — changing it means editing the agent and reading the next run. A compare mode that runs one task across several compositions is named on the index as not built, and that is still true.