1824 ET - Cerebras CEO Andrew Feldman says the demand for OpenAI's Ultrafast mode, which runs in part on Cerebras chips, well exceeded the available capacity, causing the implementation of usage-based restrictions. "After signing the agreement with OpenAI, it took us longer than we would have liked to find contracts for and bring online the substantial increase in data-center capacity required to meet the aggressive requirements in the agreement," Feldman says on a Thursday call with analysts. "As such, we find ourselves running behind schedule on the initial tranches." He adds that he understands the scrutiny investors give to the OpenAI partnership given its importance to Cerebras. Shares are up 18% after-hours.