Get Running's 64 bit iPhone update, 1.12.1, is currently on a phased roll out. If you use automatic updates, you iPhone will get the update at some point over the next week. The update started on Monday 28th August. So far, 2% of users have the update and it seems to be going well. No crashes have been logged, and I've not had any feedback about issues.
As well as brining 64 bit compatibility, the update has a new audio system. It supports podcasts better (by pausing them rather than fading them down), and does this automatically (you don't need to tell Get Running to do this thanks to some iPhone features). It should generally be more robust to audio problems (such as the whole phone's audio system occasionally crashing!). A few bits of the UI are tidied up too.
If you want to get the update sooner, you can download it manually any time using the "App Store" App on your device.
Thank you, and Happy Running!