[Bug]: AttributeError: 'Gemma3Config' object has no attribute 'sliding_window'

[rshakoor]

transformers version 4.55.0

🐛 Describe the bug

https://github.com/vllm-project/vllm/blob/main/vllm/model_executor/models/gemma3_mm.py#L691

In the following logic:

if (sliding_window := self.config.sliding_window) is not None:
If the attribute sliding_window does not exist in the config object (and it doesn't exist for Gemma3Config see https://github.com/huggingface/transformers/blob/main/src/transformers/models/gemma3/configuration_gemma3.py#L246), this will raise an AttributeError.

Suggested fix :

Replace the line with a safer getattr() call that handles missing attributes gracefully:

self.sliding_window = getattr(self.config, "sliding_window", None)

Before submitting a new issue...

• Make sure you already searched for relevant issues, and asked the chatbot living at the bottom right corner of the documentation page, which can answer lots of frequently asked questions.

[DarkLight1337]

Try upgrading your Transformers version. The current version of vLLM requires transformers>=4.55.2

[rshakoor]

doesn't seem like the latest version of the transformers code has this attribute in the Gemma3Config object so I don't think it would help https://github.com/huggingface/transformers/blob/v4.56-release/src/transformers/models/gemma3/configuration_gemma3.py

[DarkLight1337]

IIRC this is an attribute in the base PretrainedConfig, not specific to Gemma3.

[rshakoor]

it doesn't seem to exist in PretrainedConfig, but I do see it in Gemma3TextConfig

[DarkLight1337]

Does the code work without modifications after upgrading transformers version?

[rshakoor]

no, upgrading transformers version doesn't help

[DarkLight1337]

cc @hmellor

[hmellor]

sliding_window is not part of PretrainedConfig.

The issue appears to be ath sliding_window is part of Gemma3TextConfig, not Gemma3Config.

I'll make a PR

[hmellor]

Fix is here: #25085

[rshakoor]

thank you for the quick turnaround!