OpenAI has entered a definitive agreement to acquire neptune.ai, an experiment-tracking startup whose software the lab already uses to monitor training runs for GPT-scale models.
Financial terms were not disclosed in the companies’ public announcements. However, The Information reported that OpenAI is paying shy of $400 million in stock. Neptune was originally developed inside Deepsense before spinning out as an independent company. The startup previously raised more than $18 million in funding.
The all-stock deal is intended to deepen OpenAI’s visibility into how frontier models learn and strengthen its internal research infrastructure.
Neptune provides a “training observability” platform that logs thousands of per-layer metrics so researchers can track experiments, debug unstable runs and compare large numbers of model variants. OpenAI counts itself among its reference customers, alongside enterprises such as Samsung, Roche and HP.
The acquisition comes at a time when OpenAI is reportedly preparing for a possible initial public offering (IPO), with some speculation about a valuation as high as $1 trillion. In October 2025, the company had already reached a private valuation of about $500 billion. However, the company’s CFO, Sarah Friar, has said that a public listing is “not on the cards right now.”
The deal underlines two trends: consolidation of critical MLOps tooling into model providers, and OpenAI’s push to own more of its training stack. Neptune’s tools will become internal to OpenAI, and the lab is simultaneously taking equity stakes in partners like Thrive Holdings to embed its models inside accounting and IT services firms — a pattern that tightens integration but can increase vendor lock-in over time.