Two coding models, one released a week apart, sitting at opposite ends of the market. Claude Fable 5 is the benchmark king: it wins the hardest coding tests outright, and it charges for it at $10 in, $50 out per million tokens. Grok 4.5 lost most of those benchmarks, then answered with a price tag, $2 and $6, that makes you do a double take: about 8x cheaper on output, and it burns roughly a quarter of the tokens on the same task. So the real question isn't which is better, it's whether the gap in quality is worth 8x the bill. Mostly it depends on how hard your work actually is. Here’s the split, priced and mapped, with the one blocker that decides it for anyone in the EU.
The short answer
Fable 5 wins the hard coding benchmarks by 15 to 17 points and charges $10/$50. Grok 4.5 loses those, ties on terminal work, and charges $2/$6 while burning far fewer tokens. Outside the EU, Grok 4.5 is the cost default and Fable 5 the escalation for the hardest work. Inside the EU, Grok isn’t an option yet, so it’s Fable 5.
Same job, opposite strategies
These two models were built to win different arguments. Fable 5, Anthropic’s Mythos-class flagship, is out to be the most capable coding model on the market, and on the hardest tests it is. Grok 4.5, trained alongside Cursor, is out to be the cheapest model you’d still trust with real code, and on price it’s not close to anyone. One optimizes for the ceiling. The other optimizes for the bill.
The spec sheets even disagree on shape. Fable 5 carries a 1 million token context and always reasons before it answers, with an effort dial that quietly moves the cost. Grok 4.5 ships with a smaller listed context and runs fast and lean, around 80 tokens a second. So this isn’t two versions of the same idea. It’s two bets on what a coding model should cost.
What the benchmarks say
Start where Fable 5 is strongest, because it’s the reason to pay for it. On SWE-bench Pro, the multi-file repository benchmark, Fable 5 scores 80.4 against Grok 4.5’s 64.7. On DeepSWE 1.1, resolving real GitHub issues, it’s 70 against 53. Those are 15 to 17 point gaps, and at that size they’re not noise. On a hard, sprawling change, Fable 5 simply lands more of it, and the misses Grok 4.5 leaves behind are the kind you find in production.
Then the surprise. On Terminal-Bench 2.1, the command-line and agent test, the two nearly tie: Fable 5 at 84.3, Grok 4.5 at 83.3, a single point. So the gap is specifically about deep repository work. For the everyday loop, read a file, run a test, patch, repeat, Grok 4.5 keeps up with a model that costs eight times more per output token. That one benchmark is why the price argument has teeth.
What the price says
Now the other side of the ledger, where the numbers flip hard. Grok 4.5 is $2 input and $6 output per million tokens. Fable 5 is $10 and $50. That’s five times cheaper on input and about 8.3 times cheaper on output, before you factor in anything else.
And there’s something else. Grok 4.5 is unusually token-efficient: xAI reports it resolving SWE-bench Pro tasks with about 15,954 output tokens on average, against roughly 67,020 for Opus 4.8 at max effort, a 4.2x gap. Fable 5, which always thinks and bills the thinking as output, sits at the expensive end of that spectrum, not the lean one. So the real per-task gap between these two is wider than 8x. On a high-volume agent workload, that’s not a rounding error on the invoice. It’s the invoice.
The blocker no benchmark shows
Before the verdict, the thing that overrides all of it for a lot of readers here. Grok 4.5 isn’t available in the EU at launch. If you’re in Europe, the price and the benchmarks are academic, because you can’t run it, and Fable 5, which is available worldwide, wins by default. Worth knowing the flip side too: Fable 5 requires 30-day data retention and isn’t offered under zero-retention, so if your compliance rules forbid that, neither of these is your model and you’re back to something you can self-host.
The verdict
Outside the EU, run it like a budget with an escape hatch. Grok 4.5 is the default: most coding is normal-difficulty, high-volume work where being 8x cheaper and roughly 4x leaner beats the last fifteen benchmark points you’d never notice. Fable 5 is the escalation, summoned deliberately for the hardest repository-scale changes, the long agent runs, the problems where a run on Grok measurably came up short. Paying 8x for the top model on a task the cheap one handles fine is the expensive mistake here, the same one people make leaving Fable 5’s own effort dial pinned at maximum.
Inside the EU, there’s no fork yet: Fable 5, or one of the models you can actually reach, and our Sonnet 5 vs Fable 5 piece covers the cheaper Anthropic option while you wait for xAI to open the door.
Sources: xAI’s Grok 4.5 announcement and Anthropic’s Fable 5 materials; benchmark and pricing tables collated by The Decoder, July 8 2026. Grok 4.5 figures are largely xAI-reported and not yet independently reproduced; dollar comparisons use published per-million-token rates.
Frequently asked questions
Is Grok 4.5 or Claude Fable 5 better for coding?
For the hardest coding, Fable 5, clearly: it scores 80.4 on SWE-bench Pro and 95 on SWE-bench Verified, against Grok 4.5's 64.7 on Pro, and it leads DeepSWE 70 to 53. For everyday coding at volume, Grok 4.5 is close enough on many tasks and costs about 8x less on output, so it often wins on total cost.
How much cheaper is Grok 4.5 than Fable 5?
A lot. Grok 4.5 is $2 input and $6 output per million tokens; Fable 5 is $10 and $50. That’s 5x cheaper on input and about 8.3x on output. Grok 4.5 also uses roughly 4.2x fewer output tokens than Opus 4.8 on SWE-bench Pro tasks, so the real per-task gap is wider than the rate alone.
Where does Fable 5 clearly beat Grok 4.5?
On deep, multi-file work. SWE-bench Pro (80.4 vs 64.7) and DeepSWE 1.1 (70 vs 53) both put Fable 5 well ahead, by 15 to 17 points. On Terminal-Bench 2.1 they nearly tie (84.3 vs 83.3), so the gap is about the hardest repository-scale changes, not everyday agent work.
Can I use Grok 4.5 in Europe?
Not at launch. Grok 4.5 isn’t available in the EU as of July 8, 2026, while Fable 5 is available worldwide (Fable 5 also requires 30-day data retention, so it’s not offered under zero-retention). For EU teams today, that alone can settle the choice in Fable 5's favour.
Which should I default to?
If you’re outside the EU and cost matters, default to Grok 4.5 and escalate to Fable 5 for the tasks where a run measurably falls short. If you need the maximum coding quality, or you’re in the EU, Fable 5 is the safer default. Match the model to how hard the task really is, not to habit.
