Grok Build just got a significant new model option. xAI has added Composer 2.5 , Cursor's in-house agentic coding model , to its terminal-based coding agent, making it selectable from the /models menu. The move is a direct result of the deepening compute partnership between Cursor and xAI's parent entity SpaceXAI, and it puts one of the most cost-efficient frontier-level coding models directly inside xAI's own developer toolchain.
Two companies, one model
To understand why this matters, you need to know who built what. Cursor shipped Composer 2.5 on May 18, roughly two months after Composer 2. xAI then integrated it into Grok Build on June 1 , just three days after Grok Build 0.1 hit public API beta. The model itself is Cursor's work; the deployment inside Grok Build is xAI's announcement.
The backstory is a compute partnership. Cursor partnered with SpaceX to accelerate its model training efforts, explaining that it had been bottlenecked by compute and would leverage xAI's Colossus infrastructure to dramatically scale up model intelligence. Composer 2.5 itself is built on the same open-source checkpoint as Composer 2 , Moonshot's Kimi K2.5 , while together with SpaceXAI, Cursor is training a significantly larger model from scratch using 10x more total compute, with Colossus 2's million H100-equivalents. That next model is Composer 3, not 2.5 , Composer 2.5 was trained on Cursor's existing RL pipeline before the Colossus infrastructure came online.
What Composer 2.5 actually is
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