I've been excited about OpenRouter's OAuth 2.0 PKCE flow for backendless BYOK inference. I just updated my Garmin watch AI app (https://untether.watch/en/apps/byok) to run the whole flow on the watch for a seamless BYOK experience - formerly you had to copy/paste your Gemini key into settings, which was a huge barrier.

If you're building client-side/frontend apps and want to let your users BYOK, OpenRouter's PKCE flow is great for that.

Otherwise I'm still working on Untether (https://untether.watch) - a suite of digital-minimalism apps that let you stay connected and do quick actions on the watch while keeping your smartphone out of sight (and your hands).