Grok 4.5 is SpaceXAI's newest flagship model, released July 8, 2026, built for coding and agentic knowledge work. It runs $2 per million input tokens and $6 per million output tokens, ships a 500K token context window, and lands fourth on the Artificial Analysis Intelligence Index. It scores 54 to place fourth on the index, following only Fable 5, GPT-5.5, and Opus 4.8. What the launch page does not say plainly: its hallucination rate roughly doubled from the previous version. artificialanalysis

The timing nobody flagged

Grok 4.5 did not launch in a vacuum. Two days earlier, on July 6, xAI officially rebranded to SpaceXAI, debuting a new logo and an update to its X username, closing out a integration that began when SpaceX acquired xAI in an all-stock transaction on February 2, 2026. Grok 4.5 is the first model to ship fully under that new name, and it was trained alongside Cursor, the coding tool SpaceX acquired for 60 billion dollars earlier this year. None of C1 through C4 connect the release date to the rebrand. x.ai's own announcement treats it as a routine model drop. Yahoo Finance + 3

Cursor's own blog is more candid about what changed under the hood: Grok 4.5 is a mixture-of-experts model trained jointly with SpaceXAI, using trillions of tokens of Cursor data capturing real developer-agent interactions, and unlike Cursor's own specialist model, the training mix was deliberately broadened to cover STEM tasks and general knowledge work, not just code. cursorcursor

What actually got faster and cheaper

Grok 4.5 runs at 80 tokens per second and uses roughly twice the token efficiency of comparable leading models on the same tasks. Artificial Analysis backs this with harder numbers: it costs $0.31 per task on the Intelligence Index and $2.59 per task on the Coding Agent Index inside Grok Build. On raw coding-agent cost, the gap is stark: Grok 4.5 in Grok Build costs $2.49 per task, versus $11.80 for Fable 5 in Claude Code and $5.07 for GPT-5.5 in Codex, driven by using only 1.9 million average tokens per task against 7.2 million for Fable 5 and 6.2 million for GPT-5.5. x + 3

What quietly shrank

Here's the detail every competitor buries in a footnote or skips outright. Grok 4.5 ships a 500K token context window, a reduction from Grok 4.3's 1M token context, even though Elon Musk has disclosed the model is 3x larger than its predecessor at 1.5 trillion parameters. A bigger model with a smaller working memory is not the direction most labs are moving, and x.ai's own launch page never mentions the drop.

The catch: accuracy up, hallucinations up more

This is the number that matters most for anyone using Grok 4.5 for research or fact-heavy office work, and it's buried deep in Artificial Analysis's writeup rather than in xAI's marketing: Grok 4.5 scores 8 points higher than Grok 4.3 on the AA-Omniscience Index, with accuracy improving from 35% to 52%, but its hallucination rate also increased from 25% to 54%. AA frames this as a known pattern where larger models know more but state it with more unwarranted confidence. Practically: Grok 4.5 is more likely to be right, but when it's wrong, it's now more likely to sound certain about it. For legal, financial, or client-facing writing, that combination needs a human check on anything that isn't independently verifiable.

Full comparison grid

Press reaction so far

Coverage has centered on price-to-performance rather than the accuracy trade-off. The Decoder noted the model trails Fable 5 and GPT-5.5 on coding benchmarks but needs 4.2 times fewer tokens than Opus 4.8, making the benchmark gap arguably not matter much at that price. Forbes' framing leaned on Musk's own description of the model as faster, more token-efficient, and lower cost than one of Anthropic's models. Direct community sentiment from r/singularity wasn't accessible for this piece (Reddit blocked the fetch); if you're tracking real-time reaction there, that's worth checking separately.

FAQs

Is Grok 4.5 available in the EU yet? No. x.ai's own release notes state EU availability is expected in mid-July 2026. x

Is Grok 4.5 the best coding model right now? No, it ranks third among frontier coding agents, on par with GPT-5.5 in Codex and below Fable 5 in Claude Code, but at a fraction of the token cost.

Why did the context window shrink from Grok 4.3? Not explained by SpaceXAI. Artificial Analysis flags the drop from 1M to 500K tokens without giving a reason; it's plausible it's a serving-cost trade-off tied to the model being 3x larger, but that's inference, not a confirmed fact.

Does Grok 4.5 hallucinate more than Grok 4.3? Yes. The hallucination rate rose from 25% to 54% even as raw accuracy improved.