Member of Technical Staff: Agent Runtime
About the role
Ego AI, a YC-backed applied AI research lab, is hiring a Member of Technical Staff for Agent Runtime to own and evolve the core agent harness and durable execution systems for long-horizon AI agent tasks in a hybrid SF/remote setup.
Responsibilities
- Own the agent harness. Design and maintain the core agentic loop (plan → tool call → observe → repeat → finalize) as a small, legible state machine. Handle errors such as malformed tool calls, hallucinated tool names, and tool failures without crashing the loop.
- Make execution durable. Build checkpointed, resumable sessions backed by a database with step logs, idempotency keys, and clear boundary handling for at-least-once vs exactly-once semantics.
- Solve long-horizon context. Develop compaction strategy with pinned goals, running summaries, and retrieval over older state to complete 30+-step tasks within budget.
- Design for extensibility. Ship a tool registry with schemas and handlers, validate schemas before handlers run, and keep model adapters swappable in one place.
- Ship deployable systems. Implement one-command local bring-up, multi-backend persistence (Postgres/SQLite/Cloudflare), clean HTTP APIs, secrets hygiene, and per-user durable agent instances.
- Support the team. Unblock product engineers, pair on extensions, and review agent-adjacent designs.
- Projects ownership. Productionize the Ronin core, per-user durable personal agents, and an evaluation/reliability harness.
Qualifications
- 3+ years building backend or infrastructure systems with production ownership of stateful services.
- Hands-on experience building LLM agent systems: tool-calling loops, defensive handling of model output, budget management.
- Deep grasp of durable execution: checkpointing, idempotency, outbox/step-log patterns, and failure-window reasoning.
- Deliberate context-management for long-horizon tasks and ability to defend trade-offs.
- Strong API and data-model design with clean persistence and Docker-compose readiness.
- Clear written communication; ability to produce architecture docs readers understand.
Skills
About ego
Character AI + Roblox :persistent, sapient AI characters in 3D worlds
Ego AI is building Character AI + Roblox. Our conviction is that 3D embodiment, shared activities in games and AI imbued with human-like personalities will solve the existing problems of low-stakes, shallow and generic interactions that impact retention in consumer AI chat experiences. We’re fine-tuning a foundation model for characters to behave in human-like ways—indistinguishable from real people—and building a UGC platform around it to allow users to create, experience and form meaningful connections & mutual stories with these AI characters. On our platform, simworld, users will be able place the characters in a Stardew Valley style simulated town, where the AI characters will live, work and play, leading rich internal lives. Users who deepen bonds with these AI character friends can invite them out with them to Discord, Minecraft or even a Netflix-n-chill session. Our Character engine, ego AI, built on top of Unreal, will allow users to create, deploy and even monetize their characters across any surface that supports our CCProtocol. The first use case for our characters will likely be DnD-style roleplay, Minecraft RP, and Twitch streaming. Characters will always live and exist in Simtowns with other AIs (and humans) where they will all lead varied internal lives replete with conflict, danger, opportunity, and love…just like humans in the real world! During YC, we used our engine to build TownWorld - a 3D interactive Twitch live stream of the Stanford generative agents paper (https://www.twitch.tv/townworld). To the best of our knowledge, it's the first ever AI 3D simulation of a small town in real time YC Launch - https://www.ycombinator.com/launches/KeD-ego-an-ai-native-3d-simulation-engine-getting-us-closer-to-the-matrix-one-pixel-at-a-time Demo video: https://docsend.com/view/mzf6i7kiwkkgg669 AI 3D TownWorld video: https://docsend.com/view/ig6t2shuz26z7wha
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