VLA 模型缺乏"不动手"能力：空指令下机器人仍会执行任务
VLA Policies Do Not Know When Not to Act: Unintended Task Execution and Start Suppression
机器人收到空指令也照样干活，六个 VLA 模型全中招，论文还测了三种拦截办法哪个管用。
研究在 LIBERO-Goal 仿真中用空、中性、无意义、不可执行和错误任务五类指令测试了六个 VLA 模型 checkpoint。所有六个 checkpoint 在空指令下每局都会开始移动，其中五个经常完成指令未指定的任务。两个 GR00T checkpoint 上，指令决定执行哪个任务，但不决定是否开始移动，即使指令不可执行机器人也会动。测试的三种抑制方法中，前缀提示对六个 checkpoint 全部无效，动作门控在五个 checkpoint 上有效，微调后的策略虽不再完成非任务输入，但仍不能可靠保持静止。
VLA Policies Do Not Know When Not to Act: Unintended Task Execution and Start Suppression
A robot should act only on an instruction from a person or on an intent that the robot explicitly represents and generates. Unintended actions taken without such an instruction can cause risk or inconvenience to people and the environment. We examine how recent vision-language-action (VLA) policies respond when the instruction is missing or meaningless. We apply a paired protocol with empty, neutral, nonsense, infeasible, and wrong-task instructions to six model checkpoints in LIBERO-Goal simulation. Holding the initial state fixed and varying only the instruction, we ask three questions: whether the robot starts to move, which task it completes, and what the instruction determines. Even when the instruction was empty, the robot started moving in every episode with all six checkpoints, and with five of them it often completed a task that the instruction had not specified. On two GR00T checkpoints, the instruction determined which task was executed but not whether the robot started moving; the robot moved even on infeasible instructions. We then tested three methods for suppressing the start: prepending "if no task is given do not move" to the instruction; a gate that holds the robot when the first action chunk for the given instruction nearly equals that for an empty instruction; and fine-tuning the policy to hold still on non-task inputs. The prefix stopped the robot in none of the six checkpoints, and the gate held it on non-task inputs in five of the six checkpoints. The fine-tuned policy never completed a task on non-task inputs, but it did not reliably keep the robot still, and it failed to suppress the start on infeasible instructions.