Senior Backend Engineer (Firebase, Python, Twilio, AI Integrations)

We run a production backend for an AI-powered platform that helps users identify scams over voice and text in real time. It is live and functional today, built by our current lead backend engineer. We are hiring a second senior engineer to work alongside the existing codebase: validating the architecture, closing out remaining features, and adding capacity so the project is not dependent on a single developer. Stack: Python, FastAPI, Firebase, Firestore, Google Cloud Platform, Cloud Run, Twilio Voice and SMS, Stripe, LLM API integration (Anthropic, OpenAI, or similar), speech to text / text to speech pipelines. What you will do: Review and validate the existing backend architecture and Firestore data model Help close out remaining features ahead of a pilot launch Improve reliability, security, and production readiness where needed Work as ongoing backend capacity going forward You should have: Senior-level Python and FastAPI experience in production Real production experience with Firebase, Firestore, and Cloud Run Experience inheriting and working within an existing codebase, not just building from scratch Twilio voice or SMS experience strongly preferred Experience with Stripe and LLM API integrations a plus Clear written English and some overlap with US Eastern Time To apply, answer this: Describe a time you inherited another developer's production codebase. What was your approach to understanding it, identifying issues, and improving it without disrupting the existing system? Please skip generic template proposals. Repository access and full technical scope provided after a signed NDA.