Kimi K3.1 Pro vs. Claude Fable 5.2: Benchmarks, Pricing, and Which to Use

Less than three weeks apart, Moonshot AI and Anthropic each shipped a new top model. Kimi K3.1 Pro arrived in late October as Moonshot's strongest open-weight model, and Claude Fable 5.2 arrived on November 9 as Anthropic's most capable generally available model.

They're aimed at similar work, like long agentic coding runs, research, and office tasks, but they sit at opposite ends of the market. Kimi K3.1 Pro is open-weight and costs a quarter of Fable 5.2's price per token. Fable 5.2 is closed, more expensive, and, on the numbers we have, stronger on most tasks.

In this article, I'll compare the two on benchmarks, pricing, and access, put both through the same hands-on coding test, and give a recommendation on which to use for what.

What Is Kimi K3.1 Pro?

Kimi K3.1 Pro is Moonshot AI's flagship model, released on October 23, 2026. It's a post-trained version of Kimi K3, the 2.8-trillion-parameter Mixture-of-Experts model Moonshot released in July, with about 104 billion parameters active per token. The architecture is unchanged; the gains come from a much larger round of reinforcement learning across hundreds of task domains.

It has a 1M-token context window, thinking that's always on (with low, high, and max effort levels), and a faster Highspeed variant that costs twice as much. Moonshot released the full weights on Hugging Face on November 4, under a custom license.

What Is Claude Fable 5.2?

Claude Fable 5.2 is Anthropic's most capable model for general use, released on November 9, 2026. It sits above Claude Opus 5.5 in the Claude lineup and is built for the hardest technical work: large migrations, multi-day agent runs, and research problems. A version with fewer safeguards, Claude Mythos 5.2, is available only to vetted security and life sciences organizations.

Fable 5.2 has a 1M-token context window, 128K max output, and adjustable effort levels from low to max. It's 20% cheaper than Fable 5.1 and generates output up to 30% faster. For more on what changed, see our Claude Fable 5.2 article, and you can see the model in action in our Claude Fable 5.2 API tutorial.

Kimi K3.1 Pro vs. Claude Fable 5.2: Head-to-Head Comparison

Here's the catch with this comparison: there's no shared scoreboard. Anthropic's Fable 5.2 table doesn't include Kimi, and Moonshot's K3.1 Pro results compare against Fable 5.1, not 5.2. Both labs did test against Claude Opus 5.5, though, so I'll use Opus 5.5 as the reference point: how far each model lands above or below Opus on its own lab's tests.

This isn't a perfect method. The labs use different harnesses and sometimes different versions of the same benchmark, and every number here is vendor-reported. But it's the fairest picture available until independent results come in.

Notice that the two labs don't even agree on Opus 5.5's scores for two of the three benchmarks. It's a reminder of how much setup matters. 

Agentic coding

Here the two labs report different benchmarks entirely, so the Opus 5.5 reference point is all we have. In Moonshot's results, Kimi K3.1 Pro is about level with Opus 5.5 on Terminal-Bench 4.0 (65.7% vs 66.4%) and ahead on SWE-Marathon, a set of multi-hour engineering tasks (51.7% vs 46.3%). But it falls well behind on ProgramBench (31.5% vs 65.0%).

In Anthropic's results, Fable 5.2 leads Opus 5.5 on both coding benchmarks it reports: FrontierCode 2.0 (49.1% vs 45.5%) and FrontierSWE v2 (69.9% vs 62.3%).

My read: Kimi K3.1 Pro is roughly an Opus-class coding model, with a real strength in long engineering tasks and some clear weak spots, like ProgramBench. Fable 5.2 is a step above Opus. That suggests Fable 5.2 is the stronger coder overall, though Kimi K3.1 Pro may come close on the kind of multi-hour tasks where it beats Opus.

Reasoning, research, and office work

Fable 5.2 has the edge on reasoning. Besides its lead on Humanity's Last Exam with tools, it scores far higher on Terminal-Bench-Science, which tests scientific research in a terminal. That's Kimi K3.1 Pro's weakest area: at 38.1%, it trails Opus 5.5 by 25 points in Moonshot's own table.

Kimi K3.1 Pro is more competitive on research and documents. It beats Opus 5.5 on BrowseComp, a test of finding hard-to-locate information on the web (92.1% vs 90.8%), and on OfficeQA Pro, which involves analyzing financial PDFs (64.4 vs 62.2). Anthropic didn't report either benchmark for Fable 5.2, so there's no way to compare directly.

Hallucination and 3D

Moonshot's charts include two results against Fable 5.1, which give a hint of how K3.1 Pro stacks up against the Fable line:

• Hallucination: On Moonshot's internal Kimi Hallu Bench, a stress test built to provoke errors, K3.1 Pro made false claims at a rate of 5.4% without tools, compared with 11.4% for Fable 5.1. This is Moonshot's own test, and we don't have a Fable 5.2 number.
• 3D modeling: On BenchCAD, which tests rebuilding 3D objects with CAD code, K3.1 Pro and Fable 5.1 essentially tied with tools (92.7 vs 92.6). Anthropic reports a big jump for Fable 5.2 on BenchCAD, but on a different version of the benchmark, so the numbers aren't comparable.

Open weights and safety

This is the biggest practical difference. Kimi K3.1 Pro's weights are on Hugging Face, so you can run it on your own hardware, fine-tune it, or use it through a third-party host. Be realistic about the hardware, though: the checkpoint is about 1.56 TB, which means a multi-GPU server, not a workstation. And read the license before building a product on it, since it's Moonshot's own license, not a standard open-source one.

Fable 5.2 is closed, but it's available on Amazon Web Services, Google Cloud, and Microsoft Azure, which matters if your company already runs on one of them.

The two labs also handle risky capabilities differently. Moonshot removed cybersecurity data from K3.1 Pro's training before releasing the weights, which cut its score on an internal exploit benchmark from 90.5% to 81.0%. Anthropic keeps Fable 5.2's full capabilities but blocks most offensive security and research-level biology requests, offering them only through Mythos 5.2 to vetted organizations.

Pricing

Fable 5.2 costs four times as much per token. For a workload of 1 million input tokens and 250,000 output tokens, that's about $4.50 on Kimi K3.1 Pro and $18 on Fable 5.2.

Two things narrow the gap. Cache reads cost the same on both, so agent loops that reread the same context are closer in price than the headline rates suggest. And if your work can wait, Fable 5.2's batch pricing brings it down to $4/$20, the same as Kimi's Highspeed variant. The two models also use different tokenizers, so the same text won't produce exactly the same token count on each.

Hands-On Test: Building an Elevator Simulator

Benchmarks from two different labs only get you so far, so I gave both models the same task in the same coding agent: OpenCode, on my Mac, with default settings. Kimi K3.1 Pro ran through OpenRouter and Claude Fable 5.2 through the Anthropic API, both in their standard versions rather than the faster variants.

The task is a single-page simulation of three elevators in a 12-floor building. I picked it because the rules are easy to check by watching: an elevator keeps going in its direction while there are requests ahead, a car with room never passes someone waiting to go its way, and all three cars shouldn't chase the same call. There's also a rush-hour button that drops 30 people in the lobby at once. Here's the prompt, pasted verbatim:

Build a single-file web page, index.html, with inline CSS and JavaScript. No external libraries, no network requests, no build step.

The page simulates a bank of three elevators in a 12-floor building (floors 1 to 12).

Requirements:
1. Passengers appear on random floors over time, each with a destination floor. They press the up or down call button on their floor and board an elevator going their way.
2. Each elevator holds at most 8 passengers. Show the riders inside each car and the people waiting on each floor.
3. Dispatching: an elevator keeps moving in its current direction while it has requests ahead of it in that direction, then reverses or goes idle. An elevator with room must not pass a floor where someone is waiting to go in its direction. Don't send all three elevators to the same call.
4. Animate the cars moving smoothly between floors, with doors opening and closing at each stop.
5. Show live statistics: passengers delivered, average wait time, and longest wait time.
6. Controls: a speed slider (1x to 10x), pause/resume, a "rush hour" button that adds 30 passengers on floor 1 who all want to go up, and a reset button.
7. Use a fixed random seed so the same run can be repeated after a reset.
8. It should look clean and be readable at both desktop and phone widths.

When you're done, briefly explain your dispatching logic.Powered by

Getting it to run

Kimi K3.1 Pro finished on the first try in about 9 minutes. Fable 5.2 didn't. Twice, it planned for about 6 minutes, and then OpenCode stopped without writing anything or showing an error. The likely cause is OpenCode's default cap of 32,000 output tokens per response: Fable 5.2 spent the whole budget planning before it wrote any code. Raising the cap to 128,000 fixed it, and the third attempt finished in 15 minutes.

That's not a flaw in the model, but it's worth knowing if you try Fable 5.2 in a third-party coding agent the week it launched.

Watching rush hour

Here are both simulators side by side. I started each one from its own seeded state, then pressed rush hour at the same moment and set both to 4x speed.

A few things stood out to me:

• Fable 5.2 clears the lobby faster. Both get the same 30-person crowd, but Kimi's line on floor 1 stays long for much longer, while Fable's shrinks to a handful within about half a simulated minute.
• That comes down to one rule. The prompt said not to send all three elevators to the same call. Kimi K3.1 Pro took that literally and assigns one car per call. Fable 5.2 read it as "don't waste cars" and sends all three to a crowd too big for one car, and it said so in its summary. Both are reasonable readings, but Fable's works better at rush hour.
• Fable 5.2 also bent another rule, and flagged it. It lets a car skip a floor if another car is already loading there with room for everyone, which avoids two cars opening their doors for the same people. It explained the exception and offered to remove it.
• Fable 5.2's page is easier to read. The whole building and the stats fit on one screen, and each rider is a numbered chip showing their destination. Kimi K3.1 Pro's dashboard has more detail, including a status panel for each car, but on a laptop screen you have to scroll to see all 12 floors, and the riders inside each car are tiny.

Both checked their own work

Neither model just wrote the code and stopped. Both wrote test scripts that ran the simulation for simulated hours, checking that no car went over capacity, that no car passed a waiting passenger it should have picked up, and that a reset reproduced the same run. Both also checked their pages in a headless browser at phone widths. In my own checks, both pages loaded with no errors, made no network requests, and fit on a phone screen without sideways scrolling.

My verdict

Both models built a working simulator. Fable 5.2's handled rush hour better and was easier to follow, and it was more upfront about where it had interpreted the prompt. But it took longer, costs four times as much per token, and needed a config change before it would run at all. Kimi K3.1 Pro worked out of the box and followed the rules more literally.

For a quarter of the price, Kimi K3.1 Pro's result is closer than the price gap suggests. This is one task, run once per model, so treat it as a first impression rather than a benchmark.

When to Choose Kimi K3.1 Pro vs. Claude Fable 5.2

Choose Kimi K3.1 Pro if...

• Cost matters. At a quarter of Fable 5.2's price, it's hard to beat for high-volume agent work.
• You want to self-host, fine-tune, or keep the model on your own infrastructure.
• Your tasks are long but well-defined, such as multi-hour engineering jobs, web research, or financial document analysis.

Choose Claude Fable 5.2 if...

• You need the strongest results on hard reasoning, scientific work, or computer use.
• You need consistent coding performance across task types. Kimi K3.1 Pro has big gaps on some coding benchmarks, where it trails even Opus 5.5.
• You need it on AWS, Google Cloud, or Azure, or inside the Claude apps and Claude Code.

There's also a middle option. If Fable 5.2 is more than you need, Claude Opus 5.5 costs $4/$20, twice Kimi's price, and we've compared it directly with Kimi in our Kimi K3.1 Pro vs. Claude Opus 5.5 article.

Final Thoughts

On the numbers we have, Claude Fable 5.2 is the stronger model, especially on reasoning, science, and computer use. But Kimi K3.1 Pro doesn't need to win outright to be the better choice for a lot of work. It's roughly Opus-class on coding and research, it costs a quarter of Fable's price, and you can download it.

My own elevator test pointed the same way: Fable 5.2 built the better simulator, but Kimi K3.1 Pro got surprisingly close for a quarter of the price, and it worked out of the box.

If you want to get hands-on with models like these, our Developing AI Applications track is a good place to start.