(Freelance) Senior Backend Engineer (m/f/d) - Agent SDK
This is the employer's own posting, not a copy on a job board.
What we know
Is it still open?
Confirmed still open
Last checked 2d ago — checked against the employer's own applicant tracking system, which is the company answering directly.
We re-read the employer's own applicant tracking system and the posting was still there. That is the company answering directly.
How old is it?
Posted 10d ago
The date the source published, not the day we noticed it (2026-09-30). Last seen at its source 2h ago.
We have tracked this listing since 5 Oct 2026 (5 days). The employer's own board has carried it every time we have read it, most recently 2 hours ago.
Is it remote?
Marked remote on the employer's board
Their board carries a remote setting on this posting — a field they filled in, not wording we read. The location field names somewhere specific, which is usually where the team or the entity sits.
Who may apply?
Berlin, Birmingham, Romania, Paris, Munich, Poland, London, Hamburg
The description states no restriction of its own. This is the source's own tag.
Pay not stated
Similar roles pay €100.6k–153.9k/yr
Middle 50% of 18 listings that do state pay — Engineering · Senior · Germany · EUR/year. This employer has published no salary; this is what comparable listings we hold disclose, never converted between currencies or periods. How this is calculated.
Skills named in the ad
Recognised terms only, from a fixed vocabulary — this is what CV matching compares against.
Carried by 1 source
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Ashby employer's own board first seen 5d ago · last seen 2h ago
The listing
🎤 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 success with stock options
Generous perks: 30 vacation days plus your birthday off, Germany Transport Ticket, Urban Sports Club, regular company off-sites, and access to learning platforms such as Blinkist and Audible, plus free language courses
You decide when you work best, that means flexible working hours and a good hybrid set-up.
✨ Ready to talk? Apply now! 🚀
We look forward to your application and can't wait to meet you - no matter who you are or what background you have!