Musk says Grok 4.8 is ‘not as good’ as Claude Opus 5.5, ‘a masterpiece’, and that xAI rewrote its RL and inference stack in C/C++
Confirmed
The takeaway
On Nov 10, 2026 Elon Musk wrote on X that Grok 4.8 has finished pre-training but is still in RL after xAI “dumped JAX/SGLang and rewritten the entire RL and inference stack from scratch in C/C++”, and, asked how it compares, replied “Not as good.
Status
- Claim
Confirmed
- Our reporting
- High confidence
- Importance
- 2 of 5
- Last verified
- 12 November 2026
Your AI and this story
- GPT-6 Astra194 days after its cutoff
- Claude Opus 5.5133 days after its cutoff
- Gemini 4 Hydrogen224 days after its cutoff
- Grok 4.7163 days after its cutoff
None of these four assistants can know about it. The closest, Claude Opus 5.5, stops 133 days before it.
Key facts
- Technical update (4.1M views): pre-training done; RL and inference stack rewritten in C with ‘a little C++’; much SFT data cleanup
- Reply (2.1M views): Grok 4.8 ‘Not as good’ as Opus 5.5; Grok 5 ‘should exceed Opus 5.5’ in ‘2 or 3 months, with continued acceleration thereafter’
- Wccftech (Nov 11): Anthropic executives reportedly told sell-side analysts the SpaceX compute contract will not be extended beyond Q2 2027; Musk replied ‘We would be happy to take the compute back. No problem. But I think the opposite is going to happen.’ Reported terms: Anthropic pays SpaceX $3.1B per month from December; nearly a third of SpaceX’s Q3 revenue came from Anthropic
- Benzinga (Nov 10): Musk also called it ironic that Anthropic might create the superintelligence it warns about, ‘the most entertaining outcome is the most likely’
What happened
Grok 4.8 was announced for October and has slipped. Musk’s posts give the reason (an infrastructure rewrite) and an unusually candid comparison with a competitor’s model, which he also uses through Grok Bot’s routing.
Why it matters
SpaceXAI is both Anthropic’s competitor and, through its data centres, one of its largest compute suppliers; Musk’s remarks touch both sides of that relationship during Anthropic’s IPO roadshow.
Sources
5 sources from 4 sites. Numbers match the chips in the text.
5 sources: 2 primary, 3 press
Primary
- Elon Musk on X: Grok 4.8 status (Nov 10)x.com, official
- Elon Musk on X: ‘Opus 5.5 is a masterpiece’x.com, official
Press
- Decrypt: Elon Musk calls Claude Opus 5.5 a ‘masterpiece’decrypt.co, press
- Wccftech: Anthropic believes SpaceX partnership won’t last beyond Q2 2027wccftech.com, press
- Benzinga: Musk sees irony in Anthropic potentially creating superintelligencebenzinga.com, press
Changes
- Filed (news agent)