Before the start date, I began on the benchmark framework and adding SymPy conversions to functions that lacked them. The latter will make conversions from Sage to SymPy expressions better, although the reverse is still a problem. This is because Sage doesn't parse SymPy expressions as it would for Maxima, for example; it calls a _sage_ method on the SymPy objects, which means that Sage has to rely on SymPy developers to add the conversions, which hasn't been reliable so far. Maybe this should be changed in the future.
For the first week I was fortunate to be at Sage Days 48, ostensibly organized for working on the Sage Notebook, although some, including me, worked on different parts of Sage. I really enjoyed it and learned a lot. Burcin Erocal wrote some patches adding dynamic attributes to symbolic expressions (#9556) and allowing symbolic functions to take tuple arguments (#14780), which lays the foundation for implementing hypergeometric functions smoothly. I worked on getting some special function-related patches merged, including making Bessel functions symbolic (#4102), making Airy functions symbolic (#12455), and fixing numerical evaluation of log_gamma (#12521, a palindrome ticket!). I also started working on hypergeometric functions.