Weights & Biases

Weights & Biases makes software that machine learning teams use to track experiments, version datasets and models, and evaluate AI applications, functioning as a system of record for model training and fine tuning. It was founded in 2017 by Lukas Biewald, Chris Van Pelt and Shawn Lewis. Biewald and Van Pelt had earlier co-founded CrowdFlower, later Figure Eight, which Appen acquired in 2019, and Lewis was a former Google engineer. The company is based in San Francisco, and OpenAI was an early user. By 2023 it reported 700,000 users and more than 1,000 paying customers.

In May 2018 the company raised $5 million led by Trinity Ventures, with Bloomberg Beta participating and Trinity's Dan Scholnick joining the board. In May 2019 Coatue Management led a $15 million round, with angels including Nat Friedman and Richard Socher, bringing total funding to $20 million. Insight Partners led a $45 million Series B in February 2021 with Coatue, Trinity Ventures and Bloomberg Beta, taking the total to $65 million. In October 2021 Felicis led a $135 million Series C with Insight Partners, Bond and Coatue at a post money valuation of about $1 billion. In August 2023 Nat Friedman and Daniel Gross led a $50 million round at a $1.25 billion valuation, with Coatue, Insight Partners, Felicis, Bond, Bloomberg Beta and Sapphire participating, bringing total funding to $250 million.

In March 2025 CoreWeave, the GPU cloud provider, announced it would acquire Weights & Biases. CoreWeave did not disclose terms; The Information reported a price of about $1.7 billion. The transaction closed on May 5, 2025. At the time of the deal the platform served more than 1,400 organizations, including AstraZeneca and Nvidia, and TechCrunch reported that the company had been preparing for an IPO before agreeing to the sale.

The company is a case of a repeat founder team raising capital quickly in an emerging tooling category. Trinity Ventures and Bloomberg Beta entered at the first institutional round in 2018, Coatue followed in 2019 and kept investing through 2023, and later backers paid between $1 billion and $1.25 billion. The sale arrived about eight years after founding. At a reported $1.7 billion, the exit was a strong multiple for the earliest investors and a modest gain for 2021 and 2023 investors, with the buyer a newly public infrastructure company rather than an incumbent software vendor.