ValueError: <|route_start|> not found in input_ids when enabling use_classifier_free_guidance_nav for Alpamayo 1.5

[SunYuanYuan19]

It's great work! I can run Alpamayo 1.5 normally without enabling use_classifier_free_guidance_nav. However, when I set driver.model.use_classifier_free_guidance_nav=true to activate the classifier-free guidance navigation feature, I immediately get the error:ValueError: <|route_start|> not found in input_ids
Command I Run
uv run alpasim_wizard deploy=local topology=1gpu driver=alpamayo1_5 wizard.log_dir=$PWD/tutorial_alpamayo1_5_free driver.model.use_classifier_free_guidance_nav=true

Error Log

driver-0-1      | [2026-04-26 12:59:09,007][__main__][ERROR] - Exception in drive
driver-0-1      | Traceback (most recent call last):
driver-0-1      |   File "/repo/src/driver/src/alpasim_driver/main.py", line 410, in async_wrapped
driver-0-1      |     return await func(*args, **kwargs)
driver-0-1      |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^
driver-0-1      |   File "/repo/src/driver/src/alpasim_driver/main.py", line 908, in drive
driver-0-1      |     prediction = await future
driver-0-1      |                  ^^^^^^^^^^^^
driver-0-1      |   File "/repo/src/driver/src/alpasim_driver/main.py", line 592, in _worker_main
driver-0-1      |     responses = self._run_batch(batch)
driver-0-1      |                 ^^^^^^^^^^^^^^^^^^^^^^
driver-0-1      |   File "/repo/src/driver/src/alpasim_driver/main.py", line 732, in _run_batch
driver-0-1      |     return self._model.predict_batch(inputs)
driver-0-1      |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
driver-0-1      |   File "/repo/src/driver/src/alpasim_driver/models/base.py", line 248, in predict_batch
driver-0-1      |     self.predict(prediction_input) for prediction_input in prediction_inputs
driver-0-1      |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
driver-0-1      |   File "/repo/src/driver/src/alpasim_driver/models/alpamayo_base.py", line 478, in predict
driver-0-1      |     pred_xyz, pred_rot, extra = self._run_inference(model_inputs)
driver-0-1      |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
driver-0-1      |   File "/repo/src/driver/src/alpasim_driver/models/alpamayo1_5_model.py", line 113, in _run_inference
driver-0-1      |     return self._model.sample_trajectories_from_data_with_vlm_rollout_cfg_nav(
driver-0-1      |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
driver-0-1      |   File "/repo/.venv/lib/python3.12/site-packages/torch/utils/_contextlib.py", line 120, in decorate_context
driver-0-1      |     return func(*args, **kwargs)
driver-0-1      |            ^^^^^^^^^^^^^^^^^^^^^
driver-0-1      |   File "/repo/.venv/lib/python3.12/site-packages/alpamayo1_5/models/alpamayo1_5.py", line 519, in sample_trajectories_from_data_with_vlm_rollout_cfg_nav
driver-0-1      |     unguided_input_ids.append(remove_nav_text(input_ids, self.tokenizer, i)[0])
driver-0-1      |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
driver-0-1      |   File "/repo/.venv/lib/python3.12/site-packages/alpamayo1_5/nav_utils.py", line 267, in remove_nav_text
driver-0-1      |     start, end = get_nav_token_span(input_ids, tokenizer, batch_idx)
driver-0-1      |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
driver-0-1      |   File "/repo/.venv/lib/python3.12/site-packages/alpamayo1_5/nav_utils.py", line 245, in get_nav_token_span
driver-0-1      |     raise ValueError(f"{ROUTE_START_TOKEN} not found in input_ids")
driver-0-1      | ValueError: <|route_start|> not found in input_ids

Key Questions

1. When enabling use_classifier_free_guidance_nav=true, where should I define the navigation route / nav_text? Which config file or parameter is used for this?
2. How to correctly feed navigation input into the model so it automatically inserts <|route_start|>...<|route_end|> into the input tokens?
3. Does the default scene support this navigation feature? Do I need a dedicated navigation-enabled scene config?
4. What are the full prerequisites and configuration steps to enable classifier-free guidance navigation correctly?

Thank you very much for your help!

[daehyoungko]

Thanks for the detailed report. I traced this and the error is expected with the current public AlpaSim integration.

At the moment there is no public AlpaSim wizard/config option for supplying A1.5 language navigation text.
and the tutorial command enabling CFG navigation is misleading in the current release.

So for now please run Alpamayo 1.5 with: driver.model.use_classifier_free_guidance_nav=false until actual plumbing implements.

Root cause: this is an AlpaSim integration/docs gap, not a user config mistake.

FYI : To run this inference with CFG(classifier free guidance), you will need 60GB+ GPU memory. so even if plumbing is done, make sure you have 60GB+ GPU memory to test this. refer to https://github.com/NVlabs/alpamayo1.5/blob/main/notebooks/inference_nav.ipynb