I started SPT in May as an experiment with Chinese open-weight models: first DeepSeek 4 Flash, then DeepSeek 4.1 Flash. I also tried different coding harnesses, including Codex and Pi.
A public transport app gave me something useful to build while comparing them: find a nearby stop in Sofia, check when the tram is coming, and work out which connections to take. Five months later, it also works in Zürich.
