Senior Backend Engineer - Kotlin SDK for AI Agents

voize; Kraków; Hybrid; PLN 240,000 - 360,000; Full time

Benefits offered by this job

Stock options

30 vacation days + birthday off

Germany Transport Ticket

Urban Sports Club

Regular company off-sites

Blinkist/Audible learning platforms

Job summary

voize, a fast-growing startup, is building AI companions to streamline frontline workers' workflows. As Senior Backend Engineer on the Agent SDK, you will own the Kotlin foundation that powers our AI agents, shaping the runtime and client-facing contracts.

Join a team that values observability, testing, and scalable API design, with hybrid work options across Germany or remote. You’ll collaborate closely with product and ML teams to ensure a robust SDK that scales with evolving AI capabilities.

Qualifications

• Production backend experience on the JVM (Kotlin/Java/Scala) with Kotlin focus.
• Experience designing APIs and internal SDK or platform contracts.
• Experience with testing and observability; interest in AI agent systems.

Responsibilities

• Build and maintain the Kotlin SDK as an internal product with its runtime and contracts.
• Design and ship the identity/auth plumbing if needed.
• Wire telemetry, error reporting, and data privacy/anonymization for agents.
• Create architecture tests and the evaluation harness integration.
• Manage Koog version bumps and format compatibility; set shared tool output limits.

Skills

JVM backend

Kotlin

API design

Testing & observability

AI agent systems

Job description

voize, a fast-growing startup, is building AI companions to streamline frontline workers' workflows. As Senior Backend Engineer on the Agent SDK, you will own the Kotlin foundation that powers our AI agents, shaping the runtime and client-facing contracts.

Join a team that values observability, testing, and scalable API design, with hybrid work options across Germany or remote. You’ll collaborate closely with product and ML teams to ensure a robust SDK that scales with evolving AI capabilities.