【JAPAN AI】Agent Harness Engineer / English
About JAPAN AI
JAPAN AI, Inc. was established in April 2023 as a group company of Geniee, Inc. (TSE Growth Market) with the mission of dramatically expanding human potential through AI technology. We drive cutting-edge AI R&D both domestically and internationally.
Related URLs
- Our Website(https://japan-ai.co.jp/)
- Company Introduction Materials(https://www.docswell.com/s/geniee/Z828R2-japan-ai_company-deck#p1)
- Tech Blog(https://engineering.japan-ai.co.jp/)
- Careers(https://japan-ai.co.jp/recruit/)
Why We're Hiring
2025 was "the year of AI agents." 2026 is "the year of Agent Harness."
In a world where JAPAN AI STUDIO autonomously executes hundreds of workflows as "the brain of the enterprise," agent performance is not determined by the model alone. The Agent Harness - the control layer that wraps the model and manages session state, checkpoints, guardrails, context injection, and tool execution - is the key that transforms an agent from "works in a demo" to "trusted in production."
"The brain of the enterprise" approves requests, allocates resources, and discovers prospects - the Agent Harness is the heart that controls each of these actions safely, quickly, and reliably.
JAPAN AI is hiring Agent Harness Engineers to design and implement this Agent Harness in-house and build it as the shared foundation across all products.
Mission
"Design the heart of 'the brain of the enterprise.'"
Design and implement the Agent Harness - execution engine, orchestration, guardrails, memory, and model routing - that enables AI agents to operate safely, quickly, and reliably. Build the control foundation for hundreds of workflows running on JAPAN AI STUDIO, entirely in-house.
What Is an Agent Harness?
An Agent Harness is the control and execution infrastructure layer that wraps AI models. While Agent Frameworks (e.g., LangChain) handle agent construction , the Agent Harness handles agent control and operation .
Backend Engineer
What you build : Web APIs, microservices
Relationship with AI/ML : Calls ML models via API
State management : Stateless request/response
Safety controls : Authentication, authorization, input validation
/////Agent Harness Engineer
What you build : LLM-centric agent execution engines, SDKs, orchestrators
Relationship with AI/ML : Designs model routing, RAG integration, context injection, and inference optimization at the system level
State management : Agent session management, checkpoints, long-term memory, working memory
Safety controls : Guardrail/policy execution engine - a rule execution layer that controls LLM output
Role & Expectations
As an Agent Harness Engineer, you will design and implement the agent control and execution infrastructure, leveraging your AI/ML knowledge.
- Design and implement the execution engine (Graph Runtime / State Machine) with deep understanding of LLM / AI agent operating principles
- Own AI-specific system design including model routing, context management, and memory infrastructure (long-term memory, working memory)
- Design and develop the Agent SDK used by 120 in-house engineers
- Build the guardrail / policy execution engine to safely control agent behavior
- Collaborate with Research Engineers to integrate the latest research outcomes into the production infrastructure
Why You'll Love This Role
- Build the Agent Harness in-house - Design and implement the hottest architectural concept of 2026 without relying on OSS. Stand at the industry's cutting edge.
- At the intersection of AI/ML × Backend - Design and implement the agent execution infrastructure with deep understanding of LLM operating principles. Neither pure infrastructure nor pure ML - a new domain.
- Foundation software designer - This is not a job writing YAML. You will build SDKs, execution engines, and orchestrators in code. Low-level knowledge directly applies.
- Developer experience architect - Design the SDK and toolchain used by 120 in-house engineers, improving productivity across the entire development organization.
- Powering every product - In a production environment used by ~200 companies, every AI agent runs on the Harness you build.
- Rapid-growth environment - In a startup that has grown to 200+ people and 9 products in just 3 years, you will have significant autonomy in technical decision-making.
Job Description
- Agent Harness design & implementation
- Design and implement the agent execution engine (Graph Runtime / State Machine)
- Design and develop the Agent SDK - the interface for in-house engineers to build agents
- Implement session management, checkpoint, and recovery mechanisms
- Build the guardrail / policy execution engine - a rule execution infrastructure that controls agent behavior
- AI/ML System Integration
- Model routing - optimal routing of inference requests across multiple LLM providers and model types
- Design context management and memory infrastructure (long-term memory, working memory, RAG integration)
- Optimize inference pipelines (latency reduction, cost efficiency, caching strategies)
- Integrate latest research findings into the production infrastructure in collaboration with Research Engineers
- Orchestration & performance
- Develop workflow orchestration and queuing systems
- Cost/performance optimization (autoscaling, caching, batch processing)
- Inference request routing and load balancing
- Reliability & Operations
- Maintain platform uptime of ≥99.9%
- Incident response and post-mortems
- Design data access and permission management infrastructure
Key Results (KRs / Metrics)
- Agent SDK adoption rate (in-house team usage rate and satisfaction)
- Agent execution success rate (task completion rate, checkpoint recovery success rate)
- Harness-attributed failure rate (guardrail breach rate, state inconsistency rate)
- Execution latency P95 / P99 (Harness layer overhead)
- Inference cost efficiency (cost optimization through model routing)
- Developer experience score (internal NPS for SDK / API)
Team Structure
Approximately 120 members are part of the development organization.
- Agent Harness Engineers work across the following groups:
- Infra - Cloud infrastructure and SRE
- Data - Data pipelines and analytics infrastructure
- Agent Harness - Agent execution framework
- Closely collaborating roles:
- Agentic Product Engineer - Agent feature development (SDK users)
- Research Engineer - R&D and integration of new methods into the infrastructure
- AI Quality Scientist - Evaluation pipeline collaboration
- Product Manager - Product design and non-functional requirements definition
You May Be a Good Fit If You
- Bachelor's degree or equivalent practical experience in Computer Science, Software Engineering, Artificial Intelligence, Machine Learning, Mathematics, Physics, or related fields
- 5+ years of practical experience as a backend engineer
- Production product development experience in Python
- Experience designing and implementing production systems that leverage LLM / AI agents
- Experience designing and implementing distributed systems (including design and coding, not just operations)
- Experience designing and implementing RESTful APIs / gRPC
- Language requirement (at least one of the following):
- Japanese: Fluent - able to discuss product development without friction
- English: Business level
Strong Candidates May Also Have
- Agent Framework / Agent Harness design and implementation experience (LangChain / LangGraph / AutoGen, etc.)
- Production operations experience on cloud platforms (AWS / GCP / Azure)
- Understanding of RAG systems, vector databases, and memory architectures
- Model routing and inference optimization experience
- Foundation software development experience in Go (SDKs, runtimes, frameworks, etc.)
- Deep understanding of Kubernetes / container orchestration
- Event-driven architecture experience (Kafka / RabbitMQ, etc.)
- Experience implementing safety guardrails, policy execution, and AI observability
- ML infrastructure / MLOps construction experience
- Technical communication ability in English
Tech Stack
- Languages : Python, Go (backend / infrastructure), TypeScript / React / Next.js (frontend), NX
- Infrastructure : GCP (containers / K8s), Docker, Terraform
- Messaging : Kafka, Pub/Sub
- Monitoring : Prometheus, Grafana, OpenTelemetry
- Tools : Slack, Confluence, Linear, Google Workspace, GitHub, Notion
- AI Dev Support: Claude Code MAX Plan, Cursor, ChatGPT, Devin
- Workstation : Mac (Apple Silicon), dual monitor setup
Learning & Development Support
- AI Tool Usage Support
- Company covers the cost of using AI tools such as JAPAN AI SaaS services, Cursor, ChatGPT, Claude, etc.
- Development Tool Support
- If a desired development tool is paid, the cost is covered (up to ¥30,000 per year)
- Book Purchase Assistance
- Company covers the cost of purchasing books for learning, such as technical books (up to ¥30,000 per half-year)
- Language Learning / Qualification Support
- Company covers the cost of Japanese or English learning programs and qualification acquisition
- Refresh Allowance
- Company covers the cost of services used for personal refreshment (up to ¥5,000 per month)
- e.g., gym, yoga, chiropractic, aquarium, movies, theme park tickets, etc.
- Housing Allowance
- Housing allowance provided for those living in designated areas (up to ¥30,000 per month)
職種 / 募集ポジション
JAPAN AIAgent Harness Engineer / English
雇用形態
正社員
給与
年収 12,000,000円 〜 20,000,000円
Monthly: ¥857,143～¥1,428,571 (incl. 45h fixed overtime)
Stock options available
Reviews & bonuses: twice/year
OT beyond 45h paid separately
Negotiable based on experience and skills
勤務地
163-6006 東京都新宿区西新宿住友不動産新宿オークタワー ５/６階
Work Style
Hybrid work : 3 days in office, 2 days remote
Flexible working hours : Core time is negotiable
Flexibility : Future consideration for more flexible work styles is possible
Hiring Process
1. Application Review
2. Coding Assessment
3. Interviews (4-5 rounds)
4. Offer
A reference check will be conducted prior to the final interview.
会社情報
会社名株式会社ジーニー
事業内容
・広告プラットフォーム事業
・マーケティングSaaS事業
・デジタルPR事業
設立年月日
2010年4月14日
代表者
代表取締役社長 工藤 智昭
資本金
100百万円（連結、2025年3月末現在）
従業員数
877名（連結、2025年3月末現在）
本社所在地
東京都新宿区西新宿6-8-1 住友不動産新宿オークタワー5/6階
就業時間
10:00～19:00
※土日祝は休業日となります
※出向の場合は、出向先の規程に準じます
福利厚生
待遇・福利厚生
<正社員>
・書籍購入補助（半期 30,000円まで）
・リフレッシュ手当（毎月 5,000円まで）
・部活動手当（毎月5,000円まで）
・家賃手当（当社指定の駅を対象とし毎月30,000円まで）
・シャッフルランチ/ディナー（四半期に一度ランチ1,000円まで、ディナー5,000円まで）
・資格取得支援制度、英語学習支援制度（業務に必要な場合のみ）
・リフレッシュ休暇制度（3年間継続勤務した社員へ毎年付与される特別休暇 2日）
・定期健康診断（年1回）
・従業員持株会
<契約社員>
・書籍購入補助（半期 30,000円まで）
・リフレッシュ手当（毎月 5,000円まで）
・部活動手当（毎月5,000円まで）
・シャッフルランチ/ディナー（四半期に一度ランチ1,000円まで、ディナー5,000円まで）
・リフレッシュ休暇制度（3年間継続勤務した社員へ毎年付与される特別休暇 2日）
・定期健康診断（年1回）
保険
・社会保険完備
諸手当
・交通費全額支給
代表プロフィール
早稲田大学大学院卒業後、株式会社リクルート（現 株式会社リクルートホールディングス）へ入社。2010年4月株式会社ジーニーを創業、代表取締役社長に就任。2023年4月には戦略的AIカンパニーJAPAN AI株式会社を設立し、同社の代表取締役社長を兼任している。
企業成長ランキング
- Financial Times社発表のアジア成長企業ランキング2020を受賞
Financial Times社とStatista社が、アジア太平洋地域12カ国5,000万以上の企業を対象に実施した調査で、飛躍的活躍を遂げた企業500社に選出されました。
休日休暇
完全週休二日制
所定休日：土・日・祝日
休暇：年次有給休暇、夏季休暇（3日）、年末年始休暇（12月31日〜1月3日）、慶弔休暇
グループ会社
CATS株式会社（日本）
JAPAN AI株式会社（日本）
ソーシャルワイヤー株式会社（日本）
Geniee International Pte., Ltd.（シンガポール）
Geniee Vietnam Co., Ltd.（ベトナム）
PT. Geniee Technology Indonesia（インドネシア）
PT. Adstars Media Pariwara（インドネシア）
Geniee US Inc.（米国）
Geniee Software India Pvt. Ltd.（インド）
GENIEE ADTECH - FZCO（UAE）
備考
・試用期間
正社員/契約社員：1か月
・受動喫煙対策
敷地内禁煙（屋外に喫煙場所設置）
・従事すべき業務の変更の範囲
会社の定める業務
・就業の場所の変更の範囲
会社の定める場所
・有期労働契約を更新する場合の基準に関する事項（通算契約期間又は更新回数の上限を含む）
更新の上限なし