Most of it is open source. Their VLAs are based upon Gemma models + vision encoders, plus their own action experts. You can download and play around or fine tune their Pi0 VLAs from their servers directly (JAX format) or from Huggingface LeRobot safetensors port. They also have notebooks and code in their repo to get started with fine-tuning. Inference runs in a single 4090 RTX streamed over WiFi to the robot.
OpenAI is among their investors, which makes me wonder how long their work remains "open".