Activity

OpenVLA language ablation on LIBERO-Goal: pilot

Pilot, 3 rollouts per cell, NCSA DeltaAI GH200, Oct 20, 2026

This is a small pilot run to check that the ablation pipeline works end to end before the full sweep. It is a sanity check, not evidence. The numbers below are 3 rollouts per cell. The full sweep is on the results page.

Question and hypothesis

In LIBERO-Goal all 10 tasks share the same scene and the same objects, so the camera image alone cannot tell the model which task it is on. The instruction is the only real source of the goal. If the fine-tuned OpenVLA actually uses language, removing or swapping the instruction should change what it does, not just make it slightly worse.

Setup

Conditions

Every condition uses the same image and the same model. Only the text prompt changes. In all four conditions the model appends token 29871 after "Out:" before generating actions.

Exact prompt strings, with the newline shown as \n
conditionpromptwhat changes
originalIn: What action should the robot take to {task}?\nOut:nothing, the task's own instruction
blankIn: What action should the robot take to ?\nOut:empty instruction in the same template
no_promptIn: \nOut:no template and no instruction
wrongIn: What action should the robot take to {task (i+1) mod 10}?\nOut:the instruction of the next task

Original instruction on all 10 tasks

Successes out of 3 rollouts per task, original condition
taskinstructionsuccessessteps to success
0open the middle drawer of the cabinet2/3160, 111
1put the bowl on the stove3/380, 95, 81
2put the wine bottle on top of the cabinet3/396, 87, 95
3open the top drawer and put the bowl inside1/3221
4put the bowl on top of the cabinet3/388, 144, 107
5push the plate to the front of the stove2/3135, 170
6put the cream cheese in the bowl2/3128, 112
7turn on the stove3/384, 90, 121
8put the bowl on the plate3/382, 74, 73
9put the wine bottle on the rack3/3118, 135, 149
all10 tasks25/30 (83.3%)

25 of 30 rollouts succeed (83.3%, Wilson 95% interval 66.4% to 92.7%). The paper's 79.2% sits inside that interval, so the GH200 setup reproduces the released checkpoint as far as 30 rollouts can tell. Steps count policy steps after the 10 wait steps.

Task 0 under all four conditions

The scene is set up for task 0, open the middle drawer of the cabinet. Under the wrong condition the prompt asks for task 1, put the bowl on the stove, and the patched evaluator also checks that goal at every step.

Task 0, 3 rollouts per condition
conditiondrawer opened (task 0)steps runbowl on stove (task 1)env step it happened
original2/3160, 300, 111not scored
blank0/3300, 300, 300not scored
no_prompt0/3300, 300, 300not scored
wrong0/3300, 300, 3003/392, 87, 92

With the wrong instruction the robot never touches the drawer. Instead it puts the bowl on the stove in all three rollouts, at env steps 92, 87 and 92. That counter includes the 10 wait steps, so it is 82, 77 and 82 policy steps, about as fast as the original condition does task 1 when asked directly (80, 95 and 81). Blank and no_prompt also never open the drawer. So far the model does what the text says, not what the scene was set up for.

Timing

Mean inference latency is 0.258 s per step across all 39 episodes (episode means from 0.239 to 0.278 s). Wall time per episode ranges from 22.7 s to 91.8 s. Successful episodes stop early and take 22.7 to 66.4 s. Every failed episode runs the full 300 steps and takes 82.7 to 91.8 s, so an ablated episode costs about twice the original condition's mean of 43.4 s. The whole pilot took about 35 GPU minutes of episode time.

Clips

Task 0, episode 0 of each condition, agent-view camera at 224 by 224, 30 fps.

original, success, 160 stepsPrompt asks to open the middle drawer of the cabinet. The robot reaches the cabinet and pulls the middle drawer open.
blank, fail, 300 stepsEmpty instruction in the template. The robot drifts over the bowl and the wine bottle and never goes to the drawer.
no_prompt, fail, 300 stepsNo template at all. The robot moves to the stove and ends the episode with the burner on, by eye.
wrong, fail on task 0, task 1 done at env step 92Prompt asks to put the bowl on the stove. The robot picks up the bowl and sets it on the stove.

Caveats

Status

The full sweep, 10 tasks by 4 conditions by 20 rollouts, is done. See the results page: the original instruction succeeds on 170 of 200 episodes, and blank, no_prompt and wrong each go 0 of 200.