/p/2026-10-17 · explainer
Paper explainer · 2610.21088 · Xu, Ge, Guan, Li, Timmaraju, Wu and Kaffes

Nobody could tell halfway through. So ask at the end — on a copy.

Test-time search for terminal agents assumes you can score a half-finished run. A quarter of the way in, a critic reading the transcript sorted eventual winners from losers 49% of the time — a coin flip — which is why wrapping the agent in tree search bought 0.6 points for 3.8× the money. Wait until the agent calls itself done, hand the critic a throwaway fork of that state and of the state it started from, and let it run commands against them: misjudged endings fell from 36–39% to 22%, and the pass rate went from 63.4% to 72.4% at a little over half the cost of the search.

01 · The problem

Halfway through, the transcript tells you nothing

what the critic is allowed to do

02 · The mechanism

Give the critic a copy it is allowed to break

03 · The evidence

What it passed, and what it cost to pass it

which model does the probing

04 · Why I care

A rejection is a turn in the conversation, not a verdict

05 · Apply it

Your agent, your verifier illustrative

Results

What the paper actually measured

What it does not show

In practice