The best startup AI Engineers I've met are all building their own agents. I know it's a buzzword that's now a bit past the wave of peak hype (thanks @zachtratar), but I can think of no better way to immediately, viscerally, run into all the SOTA problems of Prompt Engineering, RAG, Evals, Tool use, Code generation, Long horizon planning, et al. You don't even have to try to build an agent company. Just build one that does something you want done a lot. Its basically a rite of passage like how every Jedi needs to construct their own lightsaber. Agents are the Hello World of the AI Engineer.