Sources: Project SGLang spins out as RadixArk with $400M valuation as inference market explodes

A pattern is emerging in the world of AI infrastructure: popular open source tools are transforming into venture-backed startups worth hundreds of millions of dollars. The latest example is RadixArkthe commercial company behind SGLang, an increasingly popular tool that allows AI models to work faster and cheaper.

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

The news comes as part of the team responsible for maintaining SGLang, which is used by companies like xAI and Cursor to accelerate the training of AI models, has moved to the recently launched commercial startup. RadixArk was founded as SGL in 2023 in the UC Berkeley lab of Databricks co-founder Ion Stoica.

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

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

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

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

RadixArk is not alone in making this transition from an open source project to a well-funded startup. vLLM, a more mature inference optimization project, has also made the leap. The newly formed company has been in discussions about raising more than $160 million in funding at a valuation of approximately $1 billion. Forbes reports this last month.

Three people familiar with that deal tell TechCrunch that Andreessen Horowitz is leading the investment in vLLM, although final numbers on that investment have yet to be revealed. Andreessen Horowitz declined to comment. vLLM co-founder Simon Mo characterized the information about this round in a statement to TechCrunch as “factually incorrect,” although he declined to specify which details were incorrect.

Like SGLang, vLLM was incubated in Ion Stoica’s laboratory at UC Berkeley. Stoica, a professor at UC Berkeley, is the famous co-founder of Databricks and a number of other startups.

Several major tech companies are already running their inference workloads using vLLM, and SGLang has also gained significant popularity over the past six months, Brittany Walker, a general partner at CRV, told TechCrunch. Her firm did not support either 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 companies to train AI models to become smarter over time.

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

Startups providing 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 raised $300 million from a $5 billion valuationThe Wall Street Journal reported this on Tuesday. This follows a similar move by rival Fireworks AI, which increased $250 million at a valuation of $4 billion last October.