SpaceXAI launches Grok 4.5, an 'Opus-class' model on GB300 GPUs

Grok 4.5 is SpaceXAI's play for the coding and agentic-work market that Anthropic's Claude has dominated. The model sits on a new 1.5-trillion-parameter V9 foundation and was trained on NVIDIA's GB300 hardware; Musk frames it as 'Opus-class,' claiming it beats Opus 4.8 on benchmarks while being cheaper and more token-efficient. Availability across Grok Build, the SpaceXAI console and Cursor on all plans is an aggressive distribution move aimed squarely at developers already living in those tools.

Musk added a revealing technical note: Grok 4.5 'is not yet using our internally developed C/C++ inference software that exact maps to the GB300 hardware,' and that 'doubling or more of the current speed is probably achievable'—implying meaningful headroom once the custom inference stack ships. This is the first major model launch under the SpaceXAI brand, following the company's completed rebrand from xAI on July 7 after SpaceX's February acquisition.

Competitively, 'Opus-class' and 'token-efficient' are precisely the claims developers will stress-test in real engineering work, and skepticism is warranted given self-reported benchmarks against a rival's flagship. Grok 4.5 lands the same week as GPT-5.6 and Anthropic's Sonnet 5, making this a three-way frontier scramble. Watch independent benchmarks (SWE-Bench, agentic harnesses) and whether the Cursor integration converts into sustained usage rather than launch-week curiosity.