Full-Stack Software Engineer, Mobile Apps at Hiya

ABOUT US At Hiya, we're making calls safe, useful, and human again. Voice is the most human form of communication, yet it's become one of the least trusted. Spam, scams, and AI manipulation have eroded what was once a simple way to connect. Hiya is changing that. Each month our AI voice technology analyzes 28+ billion calls, protecting over 550 million users and 800+ businesses worldwide. Partnering with a growing global network including, AT&T, Samsung, British Telecom EE, Rogers, MasOrange, Bell Canada, MasMovil, and Virgin Media O2, we're not just stopping bad actors, we're helping people feel good and confident about picking up the phone again. This is a pivotal moment for voice. As new threats and technologies accelerate, so does demand for trusted voice communication. Hiya is growing 40%+ year over year, expanding globally, and defining what voice becomes next. Join us. You won't just work on what voice is today, you'll shape what it becomes tomorrow: smarter, safer, and genuinely worth answering again. ABOUT THE ROLE You will own features end-to-end. That means holding a piece of work from contract through rollout across whichever surfaces it needs to touch, whether that's our TypeScript/Node backend, the iOS app, the Android app, or all three. Some features live mostly in the API layer. Some require real client work on one or both platforms. The job is to deliver the whole thing, not to hand off the parts that aren't your home surface. This is a builder role. We want someone who likes shipping, can hold a feature from contract through rollout, works across stack boundaries without friction, and gets things in front of real users. WHAT YOU'LL DO In the first ninety days, expect to: - Ship meaningful production code on one of our two products. We care less about scope than about you owning it end to end. - Define and defend an API contract with mobile and design before writing the feature behind it, and iterate on that contract as you learn. - Develop a point of view on how the team's agentic workflow is serving you, and raise the places where it isn't. WHAT WE ARE LOOKING FOR These are habits, not credentials. We will probe them in conversation. We don't care much about your résumé. We care about how you think and execute, and we will test that live in the interview. - Full-stack by instinct. You are comfortable moving between the API, the data layer, and the client code that calls it. You have opinions about where logic should live, and you've shipped features where you had to decide whether something belonged on the server, on the client, or at the edge. You don't need to be equally strong on iOS, Android, and backend on day one. You do need to be the kind of engineer who picks up whichever surface a feature requires and ships it, rather than the kind who stops at the boundary of what they already know. - Context engineering over prompt engineering. You've internalized that the useful lever usually isn't the prompt, it's what the model sees before the prompt runs. You have opinions about selection, compression, ordering, and isolation of context. You know context rot is real and you have strategies for it. - Plan-first on non-trivial work. You don't one-shot real features. You plan, stage, and iterate. You separate exploration from execution. You read plans before you run them, and you edit them. You know why a chain of "good enough" agent decisions stacks into a bad outcome, and you have habits that prevent it. - Contracts before code, built with product and design. On meaningful work, the agent does not touch the keyboard until there is a clear contract: what the behavior is, what the acceptance criteria are, what the interfaces look like. That contract is built with product, design, and the engineers who will integrate against it. Agents are literal-minded and will build the wrong thing at speed if the contract is underspecified. You treat the contract as a living artifact, not a PRD you wrote once and forgot about. - Multi-model and multi-agent routing. You use different models for different jobs. You're comfortable running agents in parallel on separate worktrees when work decomposes cleanly. You know when to spawn a sub-agent and when to stay in one context, and you can articulate the tradeoff. - Taste formed by shipping. You have opinions about which parts of the agentic stack are earning their keep today. You have changed your mind at least once in the last six months. You can defend your current position and tell us when you last updated it. WHAT WE DO NOT FILTER ON - Years of experience. - Familiarity with our exact stack on day one. - Leetcode performance. HOW TO APPLY Send a short note, under 500 words, that answers three things. An artifact. Point us at something you have built or meaningfully shaped. A set of skills, a sub-agent you rely on, a slash command library, a hook set enforcing a team quality gate, a rule file with real thought behind it, a contract template that changed how your team works with product. Public repo preferred. Private is fine if you can describe it in enough detail that we can tell it is real. A tension you have resolved. Tell us about a time your agent-assisted workflow produced output that looked right and was actually wrong. What was the failure mode? How did you catch it? What did you change so it wouldn't happen again? Which product do you find more interesting as a problem, and why? You'll work across both Spam Blocker and AI Phone in this role, so this isn't about placement. We want to see how you think about the product space. A link to your GitHub profile is highly encouraged, or other examples of work you can share. Resume is optional in the first round, and we won't read it before we read your response to the questions above. HOW WE WORK Hiya is not a passive environment. We expect people to take ownership, form opinions, and engage directly with hard problems. We work with a high degree of transparency and autonomy. Context is shared openly, and decisions are discussed, challenged, and then made. Once a call is made, we commit and move forward. You’ll be expected to work through ambiguity, weigh tradeoffs, and take responsibility for results, while keeping a high bar for quality and customer trust. Every team member at Hiya is expected to live our core values: - Serve, our customers and partners by holding a high bar for trust and quality - Own, share in success and open up to failures - Lead, listen, show up with a point of view but commit entirely once a decision has been made - Improve, even if it means changing course or contradicting ourselves - Do, rather than observe Benefits - 25 holiday plus bank holidays - Opt in salary sacrifice pension scheme (company full 4% of basic salary contribution) - Paid parental leave - Private medical insurance through Vitality (including dental & vision) - Employer-paid life insurance 2x base salary - Donation Matching for a charity of your choice (up to $1,000/ year) - WFH equipment stipend - $1,000/year in Professional Development funds - Lunch provided on in- office days This position is based in London, UK. Office post code: W1F 8WE COME WORK WITH US! We're building a team with diverse perspectives, identities, and professional experiences. We evaluate candidates through a business lens and believe that diversity and unique viewpoints make our company stronger, more dynamic, and a great place to build a career. We've been recognized by Built In, GeekWire, Comparably, G2, Forbes, and Deloitte Technology Fast 500 for our culture, innovation, leadership, compensation, and more. At Hiya, we're a people-centric company focused on helping each employee grow both personally and professionally. We create a culture of support and empowerment that challenges the status quo, resulting in an energized team that's passionate about their work. You'll love working here if you're looking for an innovative challenge that's disrupting an industry. Come join us!