Senior Backend Engineer

About Blue: Blue is building a new kind of phone, with your chief of staff built in. Blue sees what you do and reads every notification, text, and email for you. Based on everything it’s learned about you, it decides what to do with each one: handle it and leave you an FYI, or draft a reply and wait for your OK. Anything in your life is one ask away from being off your plate. Blue can manage complex long term tasks across apps

Delegation this deep isn’t possible from a single agent in an app. It takes owning the operating system, the whole intelligence stack, and, ultimately, the hardware. Today the Blue OS runs on Google Pixel hardware while our own hardware is in development. We’re Y Combinator-backed, seed-funded, going into our series A, and our first customers already use it as their daily phone.

The role

You will own the servers behind every Blue phone: the assistant's backend, messaging, the password vault, iPhone migration, and the infrastructure they run on. You will set the bar for how we review, deploy and operate code. Because we are working on an OS, this role is as much about reliability, security and review, as new features. 

What you'll own

• Reliability: Monitoring and alerting, on-call, incident response and postmortems, and tested backups with regular restore drills
• Deploys: Repeatable, staged releases with a fast rollback.
• Data and security: Least-privilege access to production, secrets management, and the systems that hold customers' passwords and personal data
• Capacity and limits: Rate limits, payload and token budgets, query costs, and LLM spend per user, worked out, and smoothly balanced with on device models before they cause an outage
• Review and mentoring: Reviewing changes from teammates and AI agents, and helping early-career engineers grow into strong ones

Our stack

Node.js (Express, WebSockets), PostgreSQL, AWS (RDS, S3, ECS), Google Cloud KMS, Firebase and Twilio. We use LLM APIs from Anthropic, OpenAI and Google, including Realtime voice.

What we're looking for

• You have carried a pager for a product with real users
• You have been through a launch or a growth spurt, and you know what breaks first
• Strong PostgreSQL: schema design, migrations without downtime, query tuning, and locking under concurrency
• Security instincts: you treat a password vault and production access with the care they need
• You do the arithmetic early: body sizes, token budgets, timeouts, growth
• You give real reviews, keep PRs small, and have mentored junior engineers
• You are comfortable owning infrastructure end to end, from architecture to on-call
• You work well with ambiguity and can move quickly without sacrificing quality
• You want to make a Blue Phone your daily phone

Nice to have

• Production experience with LLM APIs: latency, cost, streaming, and evaluating quality
• Experience with infrastructure as code and observability tools
• OS, Security, or Android development experience
• Experience reviewing AI-generated code, or working with coding agents

Why join now

• You will be the most senior engineer in your domain on a small team, hired to set our standards for running in production
• Your work goes straight to customers who rely on their phone every day
• Even though we use AI tools for most of our development, we have gone through a lot of effort to ensure that our infra is not AI generated slop, and you get to carry that torch

We're also planning on hiring for other engineering positions very soon across ML, security, infra and backend at varying levels of seniority. If you are interested in Blue but you don't match the job descriptions we have listed, please get in touch with a brief about what you do and what you would like to work on at Blue. You will be considered for the other positions immediately as they open.