Senior Backend Engineer – Communications (USA Only - 100% Remote)

About Us

Since 2013, we’ve been building a CRM that gets out of your way and helps your team sell more, faster. Now we’re building AI into every part of it, so Close does the busywork and your team does the selling. No manual data entry, no 10-click workflows. Just communication-first, AI-powered sales software designed to help you succeed and scale.

We're bootstrapped and profitable which means we answer to our customers and play by our rules. We're proud of our 120-person, 100% remote team, focused on building Close so that no small, scaling business fails because it can't figure out sales.

Our Stack

Our backend tech stack consists primarily of Python Flask web apps with our TaskTiger scheduler handling many of the backend asynchronous task processing chores. Our data stores include MongoDB, PostgreSQL, Elasticsearch, and Redis. The underlying infrastructure runs on AWS using a combination of managed services like EKS, MSK, RDS and ElastiCache and non-managed services running on EC2 instances. We have CI/CD pipelines that build Docker images, run automated tests and deploy to Kubernetes clusters. We also use these images in our local development environment allowing coding locally against all of our services. We have a well-documented public API that is consumed by our front-end JavaScript app as well as numerous integrations. Our infrastructure is heavily automated using Terraform, Ansible and other AWS tools.

We love open sourcing our code and ideas on our GitHub and on The Making of Close, our behind-the-scenes Product & Engineering blog. Check out our open source projects like SocketShark, TaskTiger, LimitLion and ciso8601.

AI is both how we build and what we ship, and that's reshaped what engineering looks like. This is a transformation we’re embracing and find deeply exciting.

About the Role

Close moves 7 million minutes of call recordings, millions of sales emails, and a steady volume of SMS through our pipes every month. The Communications team owns that entire surface — and the job got trickier in the last year, because real-time calling is now a real-time AI problem. When a customer tells our AI Agent Chloe to make a call, everything that happens from that moment on — the live call, the conversation itself — belongs to this team.

We're looking for someone energized by both sides of the role: the distributed-systems challenges and the AI challenges.

One thing to know up front: we do move people between teams as the work shifts. Most engineers here end up on more than one team over their time at Close — this team is where you'll start, but over time you'll likely have the opportunity to work on many different projects.

This role is open at multiple levels — Software Engineer, Senior, and Staff. You don't need to pick one when you apply: we'll calibrate together during the process.

You Are

• A seasoned engineer. Python is our backbone, but perhaps you've worked across Go, Rust, or TypeScript. You pick the right tool for the workload rather than retreating to what you know.
• Deeply experienced with email and calendar platforms. IMAP, sync protocols, calendar APIs, and the thousand edge cases of oddly configured enterprise mail servers. This is the experience that makes someone successful on this team fastest.
• Fluent in real-time and async distributed systems. WebRTC, WebSockets, queues, streaming. You've debugged a production incident where latency budgets didn't hold.
• Opinionated about AI in real-time workflows. You've built or used live transcription, voice agents, or in-the-loop AI features. You have a view on what's ready for production versus what's still a demo.
• At home in the gnarly bits. Telephony providers, codecs, retries, eventual consistency. You're drawn to the systems where edge cases actually matter. Deep Twilio or similar telephony experience is a big plus (not a requirement — but a game changer off the bat).
• Working with AI in your day-to-day. You use AI tools in your own workflow to ship faster, write tighter code, and reason about unfamiliar parts of the codebase.
• A builder first. You'd rather get a sloppy v1 in front of fifty customers than spend three weeks on abstractions. You ship.

You Will

• Overhaul how Close syncs email and calendars. Our sync engine has run for a decade; we're making a serious, ground-up investment in its performance and reliability. Millions of sales emails and calendar events, and when it breaks, customers feel it within ten minutes. You'd be in the middle of one of the biggest infrastructure rebuilds at Close.
• Take voice agents further into the call. We own the live conversation layer for Chloe's calls, and there's a lot of work ahead expanding our voice agent capabilities and infrastructure — including custom models tuned for conversational edge cases like voicemail and automated phone-tree detection (turns out "wait for the beep" is a hard AI problem).
• Solve inbound. So far Chloe makes calls; next she answers them. An inbound conversation can go anywhere — which raises real questions about specialized agents, a receptionist layer, and seamless call routing between them. Largely unexplored territory.
• Build native scheduling. Core calendar scheduling capabilities inside Close, plus more powerful scheduling for our agents. Various projects landing over the next 6–12 months.
• Design human orchestration of an agentic workforce. Agents create work for humans too — things to review, approve, respond to. How do we surface what's happening inside the CRM so each person engages with what actually needs them? A genuinely open product-engineering problem.
• Push connect rates and answer rates. Phone number pooling, local presence, branded calling, reputation monitoring. Real revenue impact, real telephony plumbing.
• Move our streaming and event substrate forward. Kafka, Redis, pub/sub. The plumbing the rest of the product runs on.

Tech you'll touch: Python, Twilio, WebRTC, WebSockets, AssemblyAI, ElevenLabs, Kafka, Redis, PostgreSQL, MongoDB.

Benefits

• Compensation: Competitive pay plus an organization-wide goal-based bonus
• Paid Time Off: ~5 weeks of PTO to start. Plus a 1-week all-company Winter Holiday Break and paid US holidays. You'll earn 2 extra days for every year you're with Close.
• 80% Work Option: Work with your manager to choose between a standard 5-day week or a 4-day week at 80% pay
• Parental Leave: Paid leave for primary and secondary caregivers
• Sabbatical: A 1-month paid sabbatical every 5 years with the team
• Healthcare (US residents): Two medical plans with Close covering 99% of your premium, plus Dental, Vision, HSA, FSA, and company-paid Long-Term Disability
• 401k (US residents): We match your contributions up to 6%, vested immediately

Our Values

Build a house you want to live in - Examine long-term thinking and action

No BS - Practice transparency and honesty, especially when it’s hard

Invest in each other - Build successful relationships with your coworkers and customers

Discipline equals freedom - Keep your word to yourself and others

Strive for greatness - Constantly challenge yourself and others

Learn More

Listen to our CEO and Founder, Steli Efti, tell the story of Close’s journey in the $0-30m Blueprint. 

Watch our culture video from our 2023 team retreat in Milan. Every year our entire team gathers in person to build connection, foster cross-functional collaboration, and have fun. In 2027, we're headed to Dusseldorf, Germany!

Explore our product. Check out a demo!

Our Hiring Process

We ask a few role-specific questions as part of our application process. These questions are designed to help us learn more about you from the start, so please answer each one thoughtfully. We see this as an opportunity to get to know you beyond your resume.

We use AI tools daily at Close and expect candidates to do the same. In evaluating your application, we aim to get a sense for you - the way you think, how you communicate, the work you've done. Applications that read as fully AI-generated will not be considered.

Regardless of fit, you can expect to hear back from our team with an update on the status of your candidacy.

If you progress to the interview process, you'll receive a full outline of the role-specific steps in your first touchpoint with us. We do our best to make the hiring process clear and human.