The legal structure is a convertible note, lease-back structure. The IP assets are held in a Special Purpose Vehicle (SPV), which is how virtually all of the Fortune 500 companies hold their IP.
The SPV grants an exclusive license to the startup with a buyout option. The startup can exercise the buyout option at any time.
Sometimes, BlueIron has held patents for 3, 6, or 12 months and the company exercises their buyout option. In other cases, the startup has a high cost of capital and it makes sense for them to pay over time.
The convertible note aspect of financing means the startup has an option to convert BlueIron to equity.