{"id":870,"url":"https://alion.io/job/character-ai-principal-research-engineer-post-training","title":"Principal Research Engineer, Post-Training","company":{"id":36,"name":"Character.AI","domain":"character.ai","url":"https://alion.io/company/character-ai","size_band":"51-200","is_staffing_agency":false,"employer_type":"direct","is_intermediary":false,"listed_via":null,"ats_vendor":"Ashby","truth_index":{"grade":"D","score":40,"open_postings":13,"ghost_share":1,"stale_share":0,"repost_share":0,"time_to_fill_p50_days":null,"computed_at":"2026-10-22T06:10:10Z"}},"role":"AI/ML","role_family":"AI/ML","seniority":"lead","employment_type":"full_time","work_mode":"on_site","remote_scope":null,"remote_scope_basis":null,"remote_working_hours":null,"hiring_geo_confidence":"structured","locations":["Redwood City, United States"],"countries":["US"],"hiring_countries":[],"hiring_countries_total":0,"salary":{"min":275000,"max":400000,"currency":"USD","period":"year","gross":null,"usd_annual":400000},"salary_estimate":null,"experience_years_min":null,"visa_sponsorship":false,"relocation_package":false,"has_equity":false,"technologies":[{"name":"A/B Testing","optional":false},{"name":"Machine Learning","optional":false},{"name":"Post-training","optional":false},{"name":"Qwen","optional":false},{"name":"Reinforcement Learning","optional":false},{"name":"SFT","optional":false},{"name":"World Models","optional":false},{"name":"Docker","optional":true},{"name":"Kubernetes","optional":true}],"status":"live","first_seen_at":"2026-06-22T12:36:20Z","employer_posted_date":"2026-06-22","last_verified_at":"2026-10-22T23:37:32Z","board_verified":true,"closed_at":null,"days_open":122,"trust":{"level":"ghost","repost_count":0,"flags":["stale","company_stale"],"days_open":121},"description":"About the Role and Team As a Principal Research Engineer on the Post-Training team, you will drive the technical vision, execution, and evolution of the systems that transform foundation models into intelligent, engaging, and aligned products. Specifically, your team focuses on post-training of top-tier OSS LLMs (such as Mistral and Qwen) to power the highly immersive role-playing chat features of Character.AI.\nYou will lead initiatives spanning data, algorithms, infrastructure, and evaluation, helping define how our models learn from feedback and improve over time. This is a highly cross-functional role that combines deep technical expertise with organizational leadership. You will partner closely with researchers, engineers, product teams, and infrastructure teams to identify the highest-leverage opportunities for improving model performance and user experience. Your work will directly shape the conversational experiences of millions of users every day. At Character.AI, you will have the opportunity to influence both the direction of our research and the systems that bring it into production, helping build the next generation of AI entertainment.\nWhat You'll Do\nTechnical Leadership & Mentorship: Define and drive the technical roadmap for mid- and post-training systems, balancing research innovation with production reliability and scalability. You will mentor and grow a team of researchers and engineers through technical guidance, design reviews, and career development. Establish best practices for experimentation, model development, and deployment.\n\nResearch & Model Development: Lead the development of alignment algorithms, optimization techniques, and training objectives to improve model capabilities and data efficiency. Drive advances in mid- and post-training methodologies including reinforcement learning, preference optimization, supervised fine-tuning, and emerging alignment approaches. Identify and execute high-impact research opportunities that improve model behavior, safety, and user engagement. Develop robust evaluation frameworks and quality signals to measure real-world model performance.\n\nSystems & Infrastructure: Lead the design of efficient training and inference systems for large-scale generative models. Architect scalable data pipelines that transform diverse data sources into high-quality training datasets. Partner with infrastructure teams to optimize distributed training, GPU utilization, and serving efficiency. Drive improvements in experimentation platforms, data quality systems, and model observability.\n\nWho You Are (Required Qualifications)\nPhD in Computer Science, Machine Learning, AI, or a related field, or equivalent industry experience.\n\nSignificant experience leading technical projects or teams in machine learning, AI research, or large-scale distributed systems. Experience scaling and mentoring high-performing research and engineering teams.\n\nDeep understanding of modern machine learning techniques, including transformers, reinforcement learning, alignment methods, and large language models.\n\nStrong track record of delivering impactful research or applied ML systems in production environments.\n\nExpertise in designing, building, and maintaining production-quality ML systems and infrastructure.\n\nExperience training, serving, debugging, and optimizing large-scale models on GPU-based systems.\n\nExperience leading teams working on large language model training, mid-training, or post-training.\n\nExperience with product experimentation, online evaluation, and A/B testing frameworks.\n\nStrong software engineering skills with the ability to write clean, maintainable, and scalable code.\n\nExcellent communication skills and the ability to influence technical direction across teams. Lead complex, cross-functional initiatives across data, training infrastructure, evaluation, and model serving.\n\nNice to Have\nHands-on experience working directly with open-source models like Mistral and Qwen, particularly adapting them via mid- and post-training for specific personas, creative writing, or role-playing applications.\n\nFamiliarity with cloud-native ML infrastructure, including Kubernetes, Docker, and modern orchestration platforms.\n\nPublications in leading machine learning conferences or demonstrated contributions to the broader AI community.\n\nAbout Character.AI\nCharacter.AI empowers people to connect, learn and tell stories through interactive entertainment. Over 20 million people visit Character.AI every month, using our technology to supercharge their creativity and imagination. Our platform lets users engage with tens of millions of characters, enjoy unlimited conversations, and embark on infinite adventures.\nIn just two years, we achieved unicorn status and were honored as Google Play's AI App of the Year-a testament to our innovative technology and visionary approach.\nJoin us and be a part of establishing this new entertainment paradigm while shaping the future of Consumer AI!\nAt Character, we value diversity and welcome applicants from all backgrounds. As an equal opportunity employer, we firmly uphold a non-discrimination policy based on race, religion, national origin, gender, sexual orientation, age, veteran status, or disability. Your unique perspectives are vital to our success.","description_format":"text","description_chars":5297,"description_truncated":false,"requirements":{"experience_years_min":null,"management_years_min":null,"team_size_min":null,"manages_managers":false,"education":{"level":"phd","optional":false},"security_clearance":false,"languages":[]},"benefits":[],"hiring_locations":[],"hiring_excludes":[],"relocation_offered":false,"industries":["LLM & Generative AI","Conversational AI","Foundation Models"],"lifecycle":[{"event":"open","at":"2026-06-22T12:36:20Z"}],"visa":[],"liveness":{"score":6,"band":"cold","label":"Long shot","p_open":1,"p_active":0.22,"p_room":0.28,"age_days":121,"expected_fill_days":30,"reasons":["conf:1","stale_co","ghost","win:tail","crowd:"],"computed_at":"2026-10-22T06:10:10Z"},"pay":{"stated_usd_annual":400000,"is_top_pay":true},"html_url":"https://alion.io/job/character-ai-principal-research-engineer-post-training","json_url":"https://alion.io/job/character-ai-principal-research-engineer-post-training.json","meta":{"generated_at":"2026-10-23T01:17:20Z","cache_seconds":300,"methodology":"https://alion.io/methodology","terms":"https://alion.io/terms","contact":"https://alion.io/contact","api":"https://alion.io/developers","about":"Alion is a live layer of people, companies and AI agents: who they are, whether they are real and active right now, what they do and how to work with them, readable by people and by agents and paid per call.","catalog":"https://alion.io/catalog.json","usage":{"tier":"crawler_verified","counted_by":"address","units_charged":1,"used_today":2156,"day_limit":null,"remaining_today":null,"minute_limit":300,"resets_at":"2026-10-24T00:00:00Z"}},"offers":[{"id":"company.slices","title":"One company in depth, by slice","status":"live","price":{"credits":0.02,"usd":0.002,"plus_per_slice":{"credits":0.05,"usd":0.005}},"unit":"per company, plus each slice with data","note":"the employer in depth","call":{"mcp_tool":"get_company","arguments":{"id":36},"rest":"https://alion.io/mcp/rest/get_company?id=36"},"human":"https://alion.io/catalog?offer=company.slices&for=job%2Fcharacter-ai-principal-research-engineer-post-training"},{"id":"market.stats","title":"A market slice: pay, demand and time to fill","status":"live","price":{"credits":1,"usd":0.1},"unit":"per slice","note":"pay, demand and time to fill for this role and place","call":{"mcp_tool":"market_stats"},"human":"https://alion.io/catalog?offer=market.stats&for=job%2Fcharacter-ai-principal-research-engineer-post-training"},{"id":"job.search","title":"Open jobs by role, technology, place, pay and visa","status":"live","price":{"credits":0.02,"usd":0.002},"unit":"per posting in a list","note":"similar open postings","call":{"mcp_tool":"search_jobs"},"human":"https://alion.io/catalog?offer=job.search&for=job%2Fcharacter-ai-principal-research-engineer-post-training"},{"id":"company.verify","title":"Is this company real and active right now","status":"pilot","price":null,"unit":"per company","request":{"url":"https://alion.io/catalog/request","method":"POST","body":"{\"offer\": \"company.verify\", \"for\": \"job/character-ai-principal-research-engineer-post-training\", \"note\": \"what you need it for\"}"},"human":"https://alion.io/catalog?offer=company.verify&for=job%2Fcharacter-ai-principal-research-engineer-post-training"}]}