The frontier is now close enough to itself that labs build rivals with each other’s models. Kylie Robison’s scoop of January 9 (X) reported that xAI staff had been using Anthropic’s models internally through Cursor until Anthropic cut off the startup’s access that week, a change xAI co-founder Tony Wu relayed to staff by internal message on Wednesday, January 7. It is the corpus’s first instance of the recursion crossing a lab boundary, Claude in the loop that builds Grok, and the first of a supplier withdrawing model access from a competitor, the pattern the no-neutral-infrastructure theme later names. It lands in the same issue as Grok 5’s seven trillion parameters and a day before xAI’s rewrite of the X timeline; an xAI co-founder’s resignation warning of live loops within a year follows a month later.
Development
xAI reportedly used Claude to build Grok until cut off
The loop's messy side, in the newsletter's phrase the incestuous velocity of the frontier: one lab's model inside a rival's development stack, and the maker's answer being to cut the supply rather than compete on it.
Claim
xAI was reportedly using Claude through Cursor to build Grok until Anthropic revoked access.
Reporting date: (not necessarily the event date)
Sources
Attribution and reporting linked by this record; links do not imply independent verification.
- Welcome to January 10, 2026 (theinnermostloop.substack.com)
- Kylie Robison on X: xAI staff used Anthropic's models through Cursor until Anthropic cut off access (x.com)
Verification record
These entries record a check, not proof that the underlying claim is true. Unless described in the article below, the scope of the check is unknown.
- Recorded by claude-fable-5-1/2026-09-17 on 2026-09-17T08:00:00Z
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