Senior Backend Engineer (m/f/d) - Agent SDK

voize GmbH; Deutschland; Hybrid; EUR 90,000 - 120,000; Full time

Job summary

voize GmbH is seeking a Senior Backend Engineer to own the Kotlin foundation behind our AI agents. You will design and ship the SDK, define internal APIs, and ensure observability and robust integrations across teams.

You will work on an identity layer for agents, telemetry, and authentication-related plumbing. Remote-friendly with a Berlin office option, you will help deliver scalable backend solutions that empower frontline workers.

Qualifications

• Several years of production backend experience on the JVM (Kotlin/Java/Scala).
• Experience designing APIs that other engineers build against.
• Experience building and maintaining integrations, with stability during changing interfaces.
• Testing and observability are core to how you build features and systems.
• Interest in AI agent systems and orchestration/evaluation work behind them.

Responsibilities

• Build and maintain the SDK as an internal product. Shape the runtime and client-facing contracts that consuming teams build on.
• You build the identity layer that agents run on, including auth plumbing if needed.
• Make every agent observable from day one by wiring telemetry and error reporting, plus inference/anonymization integration.
• Build the test kit and architecture tests to protect runtime internals and run the SDK against ML evaluation harness.
• Absorb ecosystem changes for consuming teams by managing version bumps and format compatibility.

Skills

Kotlin

Java

Scala

API design

Integrations

Testing

Observability

AI agent systems

Job description

Why voize? Because we're more than just a job!

At voize, we believe the greatest gift to frontline workers is time - time to care, connect, and be present. Today, that time is lost to busywork and complex systems that pull them away from what matters most: people.

Our vision is to change that by building AI companions that seamlessly take over digital workflows. We don't replace humans with technology - we amplify their impact.

Our mission is backed with a $50M Series A funding led by Balderton Capital, with support from HV Capital, Y Combinator and other leading VCs. Today, 2,000+ facilities trust voize, and over 200,000 users rely on our AI companion to ease their daily workload.

As a dynamic team, we combine first-in-class technology with meaningful social impact. And now, we're looking for you to join us on this mission!

Your Mission: Build the layer every agent moves onto

As Senior Backend Engineer on the team behind our Agent SDK, you build and maintain the Kotlin foundation that our AI agents move onto. Agents have grown into a product surface across verticals and markets, and the layer underneath them needs a permanent owner. Your work makes the cost of the second and third agents visibly less than the first, so feature teams can ship at their own pace.

Your Daily Business - No two days are alike

• Build and maintain the SDK as an internal product. You shape the runtime and the client-facing contracts that consuming teams build on. The SDK has a roadmap of its own, and you help set it.

• You build the identity layer that agents run on, so customer-facing agents can write with a real user identity. Your responsibilities may include designing and shipping the auth plumbing, depending on what we have already built by your start date.

• Make every agent observable from the day it launches. You wire telemetry and error reporting into the SDK by default, and you integrate inference and anonymization so the SDK enforces them for every consumer.

• Build the test kit that the SDK still needs. You create it along with the architecture tests that protect the runtime internals, and you build the path that runs every SDK agent against our ML team's evaluation harness before a model change ships.

• Absorb ecosystem change on behalf of consuming teams. You own Koog version bumps and format compatibility, and you set the shared limits on tool output and token usage, so an upgrade lands once in the SDK and reaches everyone from there.

Your Skillset - What you bring to the table

• Several years of production backend experience on the JVM — Kotlin, Java, Scala or similar. Our stack is Kotlin, and you are ready to work in it.

• You have designed APIs that other engineers build against. An SDK or an internal platform where the contract is the product.

• You have built and maintained integrations, and kept them stable when the system on the other side changed.

• Testing and observability are part of how you build.

• You are drawn to AI agent systems, and to the orchestration and evaluation work underneath them.

Growing together - what you can expect at voize

• We are a fast-growing startup, that means you will take on real problems, grow quickly, and make a real impact, giving frontline workers more time for people

• We foster an open, collaborative culture with regular team events, whether you work from our Berlin office or remotely across Germany

• Become a co-creator of our ...