A pattern is emerging in the AI ​​infrastructure world: popular open source tools are turning into multimillion-dollar venture-backed startups. The latest example is RadixArcThe commercial company behind SGLang, an increasingly popular tool that helps run AI models quickly and cheaply

RadixArc was recently valued at about $400 million in a funding round led by Accel, according to two people familiar with the matter, a significant sum for a startup that was announced only last August. TechCrunch could not confirm the size of the funding.

The news comes as some of the team responsible for maintaining SGLang, which companies like xAI and Cursor use to accelerate AI model training, have moved to a recently launched commercial startup. RadixArk originated in 2023 as SGLang inside Databricks co-founder Ion Stoica’s UC Berkeley lab.

The startup had previously raised angel capital from investors including Intel CEO Lip-Boo Tan, the people said.

Ying Sheng, a key contributor to SGLang and a former engineer at xAI, left Elon Musk’s AI startup to become the co-founder and CEO of RadixArk. LinkedIn announcement He made it last month. Sheng was previously a research scientist at Databricks.

RadixArk’s Ying Sheng, Accel, and Lip-Bu Tan did not respond to requests for comment.

Both SGLang and RadixArk focus on optimizing inference processing — essentially allowing models to run faster and more efficiently on the same hardware. With model training, estimation represents a large portion of the server costs associated with AI services. As a result, tools that optimize the process can generate huge savings almost immediately.

RadixArk is not alone in making this transition from open source project to well-funded startup. VLLM, a more mature scheme for optimizing inference, made the leap. The newly formed company is in talks to raise $160 million in funding at a valuation of nearly $1 billion. Forbes said last month

Three people familiar with the deal told TechCrunch that Andreessen Horowitz is leading the investment in vLLM, though the final number of that investment remains to be seen. Andreessen Horowitz declined to comment. In a statement to TechCrunch, VLLM co-founder Simon Moe characterized the round’s information as “materially incorrect,” though he declined to specify which details were incorrect.

Like SGLang, VLLM was incubated in Ion Stoecker’s lab at UC Berkeley. Stoica, a professor at UC Berkeley, is the famous co-founder of Databricks as well as other startups.

Brittany Walker, a general partner at CRV, told TechCrunch several large technology companies are already running their estimation workloads using VLLM, and SGLang has gained significant popularity over the past six months. His firm did not endorse any company.

RadixArk continues to develop SGLang as an open source AI model engine. The startup is also building Miles, a specialized framework designed for reinforcement learning, which allows businesses to train AI models to get smarter over time.

While most of its tools remain free, RedixArc has started charging fees for hosting services, a person familiar with the company told TechCrunch.

Startups that provide inference infrastructure for developers have seen a surge in funding in recent months, underscoring the continued importance of the inference layer for AI. Baseten recently secured a $300 million $5 billion valuationThe Wall Street Journal reported on Tuesday. This follows a similar move by rival Fireworks AI, which has also emerged $250 million At a valuation of $4 billion last October.