Elon Musk on Saturday announced that xAI's newest model, Grok 4.5, has entered private beta testing in SpaceX and Tesla, and that early internal evaluations show the model performing close to, and in some cases surpassing, Anthropic's Opus model.
"Grok 4.5, based on our 1.5T V9 foundation model, with Cursor data added in supplemental training, is now in private beta at SpaceX & Tesla. Early evals show performance close to, perhaps exceeding Opus," he wrote on X.
The supplemental Cursor data used to train V9 was from developer workflows, multi-file edits, refactors, and iterative correction cycles, which xAI has positioned as a way to sharpen the model's coding performance. Cursor is the AI coding assistant SpaceX agreed to acquire earlier in June.
Musk said reinforcement learning is continuing to improve the model and that "Grok Build," xAI's coding-agent harness, is being refined daily. He framed the SpaceX and Tesla deployment as an internal proving ground before any wider release.
Musk said SpaceX will ship a completely new model, trained from scratch, every month for the rest of the year.
Grok 4.5 marks the latest entry in a model line that's been hard to track even for close observers. xAI's V9-Medium model —the 1.5 trillion parameter, Cursor-trained system — was first announced by Musk in late May, with some reports speculating it would ultimately ship as "Grok 5," while others expected it to land as an interim 4.x release.
The "close to, perhaps exceeding Opus" claim comes from Musk's own account of internal evaluations and no third-party benchmark results have been published.
The Cursor deal
SpaceX will buy the startup behind the popular AI coding agent Cursor, Anysphere, for $60 billion in an all-stock deal to boost its presence in the lucrative enterprise AI tools market.
The deal gives xAI, acquired by SpaceX in February, a stronger hold in coding, one of the first areas that have helped companies turn AI into a source of revenue from businesses.
Cursor is among several Silicon Valley startups that have helped developers use AI to automate coding, making it a key rival to market leaders Anthropic and OpenAI. But a lack of access to computing power has hampered Cursor's growth.
SpaceX had been eyeing Cursor for months and in April unveiled an option to either buy the startup for $60 billion later this year, or pay $10 billion for a partnership.
