Full-Time
Machine Learning Engineer
Posted on 10/31/2025
LMArena
11-50 employees
Crowdsourced LLM evaluation and leaderboard
Compensation Overview
$210k - $250k/yr
California, USA
Remote
Hybrid role; on-site in SF Bay Area and remote option.
 AI & Machine Learning (2) |
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- Strong programming skills with the ability to work across the stack in a typical recommendation system or large language model stack
- Experience in deep learning, language models or reward model training
- Experience in working with large language models for fine tuning, prompt engineering, function calling etc
- Self-motivated with a willingness to take ownership of tasks
- A passion for shipping quality products
- 4+ years of industry experience or relevant projects
- Solid understanding of statistics, and various tools and methodologies for evaluating uncertainty in a way that is specific to the given product being shipped
- Architect and build what will become our core modeling for data and evaluation products
- Own the full stack data, model training, and evaluation pipelines
- Help grow a culture of feedback and rapid product iteration as we build new features as a tight-knit team
- Conduct research into state-of-the-art evaluation methods and contribute to the long-term vision for a centralized, scalable evaluation platform.
LMArena is a crowdsourced platform for evaluating and ranking large language models using side-by-side prompts and votes, publishing a public Elo-based leaderboard. It evolved from Chatbot Arena and operates under Arena Intelligence Inc., with the FastChat framework powering its UI and backend, which remains open source. Users submit prompts, compare two anonymous model responses, and reveal identities after voting, creating a real-world, data-driven performance dataset. The company monetizes insights from model performance and user preferences to guide researchers, developers, and enterprises in model development and selection.
Company Size
11-50
Company Stage
Series A
Total Funding
$250M
Headquarters
San Francisco, California
Founded
2025
Simplify's Take
What believers are saying
- Annualized consumption run rate hit $30 million four months after September 2025 AI Evaluations launch.
- Raised $150 million Series A at $1.7 billion valuation in January 2026 from Felicis and UC Investments.
- Partners with OpenAI, Google, xAI for enterprise evaluations in law, medicine, and software engineering.
What critics are saying
- April 2025 competitor paper proves OpenAI, Google partnerships enable Elo gaming, eroding neutrality.
- OpenAI synthetic preference data replaces human voting, obsoleting leaderboards within 6-12 months.
- Hugging Face leaderboards capture 40% open model evaluations, fragmenting LMArena market share.
What makes LMArena unique
- LMArena uses crowdsourced Elo ratings from 60 million monthly conversations across 150 countries.
- Platform evaluates models in text, vision, web development, and multimodal tasks beyond static benchmarks.
- Open-source FastChat backend enables transparent, real-world human preference data collection.
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Company Equity
Growth & Insights and Company News
6 month growth
↑ 0%1 year growth
↑ 13%2 year growth
↑ 13%LMArena achieves $1.7B valuation four months after launching its product. LMArena, a startup that originally launched as a UC Berkeley research project in 2023, announced on Tuesday that it raised a $150 million Series A at a post-money valuation of $1.7 billion. The round was led by Felicis and the university's fund, UC Investments. The startup bolted out of the gate as a commercial venture with a $100 million seed round in May at a $600 million valuation. This new round means it raised $250 million in about seven months. LMArena is best known for its crowdsourced AI model performance leaderboards. Its consumer website lets a user type a prompt that it sends to two models, with the user then choosing which model did a better job. Those results, which now span more than 5 million monthly users across 150 countries and 60 million conversations a month, the company says, fuel the leaderboards. It ranks various models on a variety of tasks including text, web development, vision, text-to-image, and other criteria. The models it tests include various flavors of OpenAI GPT, Google Gemini, Anthropic Claude, and Grok, as well as ones that are geared toward specialties like image generation, text to image, or reasoning. The company began as Chatbot Arena, an open research project built by UC Berkeley researchers Anastasios Angelopoulos and Wei-Lin Chiang, and was originally funded through grants and donations. LMArena's leaderboards became something of an obsession among model makers. When LMArena started pursuing revenue, it partnered with select model companies such as OpenAI, Google, and Anthropic to make their flagship models available for its community to evaluate. In April, a group of competitors published a paper alleging that this helped those model makers game the startup's benchmarks, an allegation LMArena has vehemently denied. In September, it publicly launched a commercial service, AI Evaluations, in which enterprises, model labs, and developers can hire the company to perform model evaluations through its community. This gave LMArena an annualized "consumption rate" - as the company describes its annual recurring revenue (ARR) - of $30 million as of December, less than four months after launch. Join the disrupt 2026 waitlist. Add yourself to the disrupt 2026 waitlist to be first in line when early bird tickets drop. Past disrupts have brought Google cloud, netflix, microsoft, box, phia, a16z, elevenlabs, wayve, hugging face, elad gil, and vinod khosla to the stages - part of 250+ industry leaders driving 200+ sessions built to fuel your growth and sharpen your edge. Plus, meet the hundreds of startups innovating across every sector.
LMArena, open community platform to benchmark and compare ai models through side-by-side evaluations and user voting. Here you'll find information about their funding, investors and team.
Today, we’re excited to share a major milestone in LMArena’s journey. We’ve raised $150M of Series A led by Felicis and UC Investments (University of California), with participation from Andreessen Horowitz, The House Fund, LDVP, Kleiner Perkins, Lightspeed Venture Partners and Laude Ventures.
LMArena, a startup operating a widely cited ranking system for AI models, has raised $150 million at a $1.7 billion valuation, according to The Information. The funding round was co-led by existing investors Felicis and the University of California's investment arm. The company evaluates AI model performance for clients including OpenAI, Google, xAI and Microsoft. The new capital will fund computing power needed to run the AI models it assesses and support hiring of technical staff. LMArena's ranking system has become an influential benchmark in the AI industry for comparing model capabilities across different providers.
LMArena, an AI evaluation platform, has secured $100 million in seed funding led by a16z and UC Investments, with participation from others. The funding supports the relaunch of LMArena, featuring a rebuilt UI, mobile-first design, and new features. LMArena aims to provide rigorous, community-driven AI evaluation, focusing on real-world performance. The platform is open and transparent, helping shape AI reliability. Learn more at lmarena.ai.