Elon Musk has called Anthropic’s Claude Opus 5.5 a masterpiece in a rare admission about a rival. He also acknowledged that xAI’s upcoming Grok 4.8 will fall short.
However, Musk insists Grok 5 could overtake Anthropic’s flagship model within months.
Elon Musk Talks About Claude AI
On Tuesday, Musk replied to an X user who asked how Grok 4.8 would compare.
“Opus 5.5 is a masterpiece,” Musk wrote on X, adding that Grok 4.8 would be “not as good.”
Anthropic released Opus 5.5 on September 22. The company says it performs comparably to its higher-end Fable 5.1 on most work.
Moreover, it costs 40% less to run than the previous Opus model on typical workloads. On Terminal-Bench 4.0, Anthropic reported a 65.76% score.
By contrast, OpenAI’s GPT-6 Astra scored 57.9% on the same test.
Meanwhile, Musk has not published any benchmark results for Grok 4.8. Praise from a direct competitor is unusual in the fiercely competitive AI industry.
Can Grok 5 Really Beat Claude Opus 5.5?
Musk believes so. He said Grok 5 “should exceed Opus 5.5,” possibly within two or three months. However, he gave no firm release date.
Still, Musk often misses his own targets, so investors and users may want to treat that timeline with caution.
For now, xAI is finishing Grok 4.8. Musk said pretraining is complete, although the model remains in its reinforcement learning phase.
The team also spent considerable time cleaning up its supervised fine-tuning data. In addition, xAI replaced JAX and SGLang with a new system written in C and C++.
Interestingly, Musk credited Starlink engineers with helping build the training and inference stack. The rewrite borrows SpaceX practices, such as custom headers and precise time calculations, including leap seconds.
He called Grok 4.8 “not yet incredible,” but said its foundations now look solid.
Musk expects a soft rollout to early users later this week. Anthropic has not publicly responded to his comments.
