OLD DOGS is a module that expands FIST's ability to handle high level play by allowing agents to age into a sort of veteran status in the organization.
OLD DOG's PDF is 2 pages, with a clean, well-organized layout that uses black and white contrast to make the text pop.
Contents-wise, there's a lot of meat here, and all of it's flavorful. A Milestones mechanic is added to player Roles, tracking their progress towards their personal goals. Veteran FIST agents have a variety of directions they can go in, from burning out to fading into the background as a supporting cast member. There are also options for higher level threats or more dangerous scenarios, allowing veteran agents to stay in the field and face escalating stakes and difficulty.
Overall, the feeling here is grizzled and heroic, and it's great. If you find yourself playing a fair bit of FIST, and if characters are starting to survive multiple missions, roll these mechanics out and let the players be OLD DOGS.