Google Waltham Cross is an operational AI data center hosting an estimated 124k H100-equivalent chips — supported by 88 MW of IT power — at a capital cost of $3.3 B. We estimate that it uses Google TPU v6e and Google TPU v7 chips. The timeline of IT power and compute capacity is based on satellite imagery, our cooling equipment power model, chip availability, and chip efficiency. The facility uses advanced air-cooling instead of water-cooling to minimize water use, and is equipped for off-site heat recovery — capturing waste heat to warm nearby homes, schools and businesses for free.