Source code for LLMs. [D]

I was digging through Hugging Face’s Transformers repo and found
https://github.com/huggingface/transformers/blob/main/src/transformers/models/gpt_oss/modeling_gpt_oss.py

From what I can tell, this isn’t just boilerplate, it looks like a full implementation.
is it actually the full code on which gpt_oss is built on?
or is it a skeleton for experimentation?

Similarly there are many models in
https://github.com/huggingface/transformers/blob/main/src/transformers/models
are they really the true open source implementations?

if not, can we actually find them publicly?