SpaceX and Cursor Launch Their First Jointly Built AI Model: Grok 4.5

The Jointly Built Model: Grok 4.5's Technical Basis

On June 28, 2026, Elon Musk confirmed the specifics of the jointly trained model. Grok 4.5 is based on xAI's 1.5-trillion-parameter V9 foundation model, with Cursor's developer data added through supplemental training. The model is currently in private beta at SpaceX and Tesla, with early internal evaluations showing performance "close to, perhaps exceeding Opus."

The infrastructure behind the model is equally significant. SpaceX has been using its Colossus supercomputer cluster as the compute backbone for the joint training effort. Cursor’s contribution includes its proprietary coding model Composer and the rich dataset of developer interactions from its AI-powered code editor.

SpaceX’s official statement on June 16 made the deployment plan clear: "For the past few months, SpaceXAI has been jointly training a model with Cursor, which will be released in Cursor and Grok Build soon." This confirms the model will ship in both products, rather than being exclusive to one. Grok Build is xAI’s terminal-based coding agent, which launched between May 14 and May 25, 2026, making it the fourth AI lab to offer a dedicated CLI coding agent after Claude Code, Codex, and Google's Gemini/Antigravity.

Competitive Positioning in the AI Coding Market

The deal and the resulting model place SpaceX/xAI directly in the AI development-tools and coding-agent market. The April Reuters report described this as a profitable sector SpaceX was aiming to expand into.

Cursor brings an established AI-powered code editor with a large developer user base, a developer workflow platform, and its proprietary Composer coding model. The strongest documented strategic advantages in the provided sources are access to SpaceX’s Colossus compute infrastructure and the use of Cursor data in supplemental training for Grok 4.5.

Furthermore, even before the formal acquisition, xAI added Cursor’s Composer 2.5 model to Grok Build on June 1, 2026. This model scores 79.8% on SWE-bench Multilingual, compared to Grok Build's native model which scored ~70.8% on SWE-bench Verified. This move immediately improved xAI's competitive standing in AI-powered coding benchmarks.

Key Uncertainty: The Public Launch Date

While the model is real and in use, the exact public launch date remains uncertain. SpaceX said "soon" on June 16. Grok 4.5 itself is described as a private beta model at SpaceX and Tesla, not a generally available public product for paying developers, who still use Grok 4.3 on v8-small. No provided source confirms a specific Wednesday launch date for a consumer-available jointly trained model.

Summary of Key Facts