Cerebras Falls Below Its IPO Price as an OpenAI Scare Collides With Insider Selling

Shares of AI chipmaker Cerebras Systems ($CBRS) fell sharply this week, dropping below their $185 IPO price as three separate pressures — a customer-concentration scare, a major lockup expiration, and heavy insider selling — all landed within days of each other.

The OpenAI displacement scare

The most consequential piece of news came from SemiAnalysis, which reported that OpenAI's newly unveiled GPT-6.1 Sol Ultrafast tier appears to be running on Nvidia GPUs — at low batch size and roughly 300 tokens per second — rather than on Cerebras hardware. That's a sharp drop from the 750 tokens per second Cerebras delivered powering the Ultrafast tier of the earlier GPT-5.6 Sol model. Neither OpenAI nor Cerebras has publicly confirmed which hardware actually serves the new tier.

The reason this particular rumor hit so hard: OpenAI is Cerebras' largest customer by revenue backlog, tied to a multi-year, 750-megawatt inference compute deal reportedly worth more than $20 billion. On Cerebras' August 12 earnings call, CEO Andrew Feldman said OpenAI would "stay a big part" of the business next year. Any sign that OpenAI is routing its newest, highest-profile model to a rival chipmaker instead reads as a direct threat to the customer-concentration story investors bought into at the IPO.

A lockup that releases in waves, not all at once

Unlike a typical single-date IPO lockup, Cerebras' unlocks on 11 separate dates, releasing an estimated 171 million shares in total across the first 10 waves, out of roughly 238 million shares outstanding. The September 30 wave freed an estimated 19.4 to 20 million shares into public float — one of several unlock dates that had already been chipping away at the stock in prior weeks, including a roughly 26% two-session drop following an earlier wave in June.

Executives filed to sell alongside the unlock

The lockup expiration landed the same day two senior officers filed Form 144 notices covering a combined $84.3 million in proposed stock sales. Separately, CTO Sean Lie reduced his direct holdings by nearly 28% in a $25.1 million sale, with CEO Andrew Feldman also selling multi-million-dollar tranches. Insiders have sold roughly $266 million in Cerebras stock over the trailing three months. A Form 144 filing discloses a proposed sale, not a confirmed completed one, but the timing — right as the lockup opened and the OpenAI rumor spread — added to investor unease.

The case that the selloff is overdone

Not every analyst is reading this as a structural problem. Cerebras' overall remaining performance obligations — the backlog of contracted work not yet delivered — stood at $25.4 billion as of June 30, and the company has continued signing new inference partnerships beyond OpenAI, including deals with cloud startups Gimlet Labs and General Compute, broadening its customer base somewhat beyond its original anchor client. Bulls argue that a single unverified hardware report, even about Cerebras' biggest customer, shouldn't by itself undo a multi-billion-dollar backlog built across several customers.