[yushuosun]

Summary / Motivation

Closes #3648.

The transformers-dep extra currently allows transformers>=5.4.0,<5.6.0.
Releases 5.4.0–5.5.3 contain a bug in
Qwen2_5_VLForConditionalGeneration.get_rope_index where still images are
incorrectly routed through the video temporal-scaling path. Concretely,
the variable second_per_grid_t is set to a non-zero value for image
tokens, causing temporal_start to be multiplied by tokens_per_second
rather than remaining zero-scaled. The result is that every image token
receives a shifted temporal position encoding, degrading policy performance
on all Qwen2.5-VL-backed policies.

The bug was fixed in transformers 5.5.4 via
huggingface/transformers#45330 (tracking issue
huggingface/transformers#45325).

Root cause

lerobot/policies/eo1/modeling_eo1.py (line 566) calls
vlm_backbone.model.get_rope_index(...) directly through the transformers
public API. Any environment that resolves transformers>=5.4.0 to a
release between 5.4.0 and 5.5.3 (inclusive) will silently receive wrong
position IDs for still-image observations.

wall_x maintains its own local copy of get_rope_index and already sets
second_per_grid_t = 0 for images unconditionally, so it is not affected
by this dependency range.

What changed

The transformers-dep extra in pyproject.toml:

-transformers-dep = ["transformers>=5.4.0,<5.6.0"]
+transformers-dep = ["transformers>=5.5.4,<5.6.0"]

The upper bound is unchanged; only the lower bound is raised to exclude the
broken 5.4.0–5.5.3 range. All extras that pull in transformers-dep
(eo1, wallx, sarm, smolvla, pi, hilserl, xvla, peft,
libero, etc.) inherit this tighter bound automatically.

Duplicate check

• Track A – open PRs referencing Qwen2.5-VL-based policy performance degradation caused by RoPE index calculation bugs in Transformers v5.4.0 #3648: no existing PR found citing this issue.
• Track B – issue comments: issue Qwen2.5-VL-based policy performance degradation caused by RoPE index calculation bugs in Transformers v5.4.0 #3648 has 0 comments; no in-progress fix exists.

[yushuosun]

Closing because the dependency set on main has moved substantially, this branch now conflicts, and a version-bound-only change without a current regression test is no longer a good patch. I can revisit with a reproducer if the incompatibility returns.