interwhen: A Generalizable Framework for Steering Reasoning Models with Test-time Verification

Understand

Reasoning models produce long traces of intermediate decisions and tool calls, making test-time verification important for ensuring correctness.

• Existing approaches either verify only the final answer, which misses early errors, or rely on branch-and-verify strategies that explore multiple trajectories.
• We introduce interwhen, a single-trajectory verification framework that steers model behavior by providing feedback on intermediate reasoning traces.
• It addresses two key challenges.