Grok 4 Fast

Grok 4 Fast was released by SpaceXSI on Friday, Sep 19 2025.

Grok 4 Fast was built by SpaceXSI. Elon Musk's AI company building the Grok series of models. Founded in 2023 as xAI, merged into SpaceX as SpaceXAI in 2026 and renamed SpaceXSI (SpaceX Super Intelligence) that October. Cursor (Anysphere) and its Composer coding models were acquired in 2026 and are tracked here.

No. Grok 4 Fast is a closed model. The weights are not published — it is available only through the provider's own API, apps, or partner platforms.

SpaceXSI's previous tracked release was Grok Code Fast 1 on Aug 28 2025, 22 days earlier. It was followed by Composer on Oct 29 2025.