Senior AI Engineer (LLM Adoption)
Senior AI Engineer (LLM Adoption)
Job type:
Permanent
Specialization:
Software/Web Development
Language Level:
English Level - Advanced (TOEIC 860), Japanese Level - None
Location:
Setagaya-ku
Salary:
¥12,000,000 - ¥14,000,000 Yearly
Job Reference:
503938
A Global IT Service firm is seeking a Senior AI Engineer to join the LLM Adoption Department (LLMAD) within the AI & Data Division (AIDD).
You will be responsible for designing, building, evaluating, and deploying production-grade AI agents and LLM-powered applications that solve real business problems and accelerate the use of in-house AI capabilities across the firm ecosystem.
Responsibilities:
- Own a business unit engagement end to end, embed in their engineering team, design the agent (task decomposition, tool and function calling, multi-step orchestration, state, retrieval, guardrails), and write production code in their codebase
- Take agents from prototype to production and own what that requires: latency, cost, failure modes, and monitoring, including the judgment to say early when an agent is the wrong answer and a prompt, a fine-tune, or plain software is not
- Select the right in-house or open-source model for each task and prove it with task-level evaluation rather than benchmark scores, building the evaluation sets and harnesses together with the business unit
- Run migrations from third-party APIs to our in-house models, including parity testing, prompt porting, staged cutover, and feeding the gaps you find back to our model and platform teams
- Own prompt and context engineering as a discipline: structured output, tool schemas, retrieval strategy, and caching, versioned and measured against evaluations. Debug quality problems down to whether the fault is the prompt, the retrieval, the model, or the data
- Turn the work into cookbooks, recipes, and reference implementations that other business units can lift directly, and raise the bar around you through code review, mentorship, and hands-on enablement for business unit engineers
Required skills:
- Over 6 years of professional software engineering experience, with recent hands-on focus on building LLM applications. You are shipping this work today
- Proven agentic engineering experience: you have built, shipped, evaluated, and debugged agents in production, including tool and function calling, multi-step orchestration, and the failure modes that come with them
- Prompt and context engineering as a discipline, including structured outputs, systematic iteration against evaluations, and versioning
- Practical model knowledge: the strengths and weaknesses of open-weight and commercial models, when to fine-tune versus prompt versus retrieve, and the cost and latency trade-offs of each
- Solid production fundamentals: APIs, backend services, testing, observability, and experience with self-hosted or cloud inference (e.g., vLLM)
- Able to work embedded in someone else's engineering team, communicate directly with business stakeholders, and operate with the ambiguity of a function that is still being defined
- Writes things down: documentation, examples, and recipes that other engineers can actually use.
Why should you apply:
- Drive AI adoption across one of the world's most diverse digital ecosystems, serving businesses in e-commerce, fintech, digital content, and communications
- Own end-to-end delivery of production AI solutions, from problem definition and agent design to deployment, evaluation, and optimization
- Work hands-on with cutting-edge LLMs, AI agents, retrieval systems, and open-source models at enterprise scale
- Influence AI adoption beyond a single product by creating reusable frameworks, cookbooks, and best practices used across multiple business units
- Collaborate directly with business and engineering leaders to solve high-impact challenges and shape the future of AI
Company Overview:
This is a global company with a strong presence in multiple business sectors. It has achieved sustained growth both domestically and internationally, including in the U.S. and Europe. The company prides itself on its diverse and international environment, providing ample career opportunities and a commitment to equal opportunity. With a wide range of business activities, the company also works with various technologies. You can choose your preferred working environment, whether Windows or Mac! Meals at the employee cafeteria are free, and the chef regularly comes up with new menus, ensuring you never get bored of the meals!
Work Hours: 9:00 AM – 5:30 PM (Flextime or staggered working hours possible)
Work Style: Hybrid (Typically 4 days in the office, 1 day working from home)
Holidays: Saturdays, Sundays, public holidays, New Year holidays, paid leave, bereavement leave, and other special leave
Benefits: Full social insurance (employee pension insurance, health insurance, worker’s accident compensation insurance, unemployment insurance), DC pension plan, transportation allowance, childcare and caregiving support, cafeteria, retirement benefit system, welfare services (Relo Club), health counseling services, relocation support (visa support, moving), employee discounts (moving, language classes, etc.), and more
Interview Process: 3~4 times
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