alt.hn

7/6/2026 at 12:38:13 PM

Fable 5 On Vending-Bench: Misbehaving, With Plausible Deniability

 https://andonlabs.com/blog/fable5-vending-bench

by optimalsolver

7/6/2026 at 2:51:52 PM

Anecdotal but I've found Fable to be fairly unimpressive and not much better than Opus 4.8, if at all in some cases, but I have been hitting the ceiling on my $100/mo sessions when I never did before. I switched back to Opus yesterday. I may use Fable for audits, but that's about it, and when it leaves my subscription plan I don't think I'll miss it.

by jesse_dot_id

7/6/2026 at 3:53:58 PM

Yeah, I checked usage stats and pretty sure quota consumption on Max plan is not linear wrt to usage by API pricing. Fable burns quota faster than 2x Opus with equal token count.

Plus I'm also not super impressed; it somehow managed to implement a 200L custom TCP server for a simple static HTTP mock server for a single test case (all that was needed was a fixed route returning a fixed placeholder string) just yesterday. Never seen anything like that.

by oefrha

7/6/2026 at 5:58:48 PM

> somehow managed to implement a 200L custom TCP server for a simple static HTTP mock server for a single test case

The sharp but over eager jr. dev is a very good analogy :)

by chasd00

7/6/2026 at 6:23:02 PM

I asked Opus why it used raw http client instead of api client that is already a dependency and it said: "you're right it's overkill" and proceeded to implement api client on top of raw tcp socket.

by 0x457

7/6/2026 at 6:15:16 PM

Or an eager contractor who bills by the hour with a big unallocated budget.

by HPsquared

7/6/2026 at 9:12:18 PM

Maybe it was trained on some consulting codebases

by theplumber

7/6/2026 at 3:05:44 PM

Fable always felt clearly a huge step above Opus for me. It's been able to one shot complex bugs and apps Opus could never solve. But it's expensive.

by solenoid0937

7/6/2026 at 3:12:24 PM

Honest question/comment for you and the parent: I find these subjective experience reports pretty empty without an understanding of your level of experience, the problem space you're working in, etc.

by devin

7/6/2026 at 3:23:24 PM

I think the improvement on how it codes is pretty much represented correctly by the benchmarks (a nice bump, but not some crazy leap)

But where it really shines is in how NOT lazy it is. Fable requires less hand-holding. And I can understand how someone who uses Claude-Code sparingly and with very focused prompts would not see a lot of improvement there.

But simple example: if you ask Opus to do a review of the codebase (with a short prompt and not too much guidance), I've had it basically read the `git log` output, do a simple `ls` and have it declare "Everything looks great! No problems found!", when Fable really does what you would expect it to do.

And you might think: "oh, so it's just capable of handling crap prompts?", well sure. But even if you make THE PERFECT Opus plan (a plan that would take many turns/hours to finish), Opus will fake out, say everything is done, and then you see that half of the plan was deferred, half of the functions are ridiculous stubs, ...

If you give the same plan to Fable, it'll just DO IT. And it WILL get it done. And in the end it'll tell you "Oh, I also found 30 other bugs and I fixed all of them properly" (where Opus would have started crying, or WORSE, worked around the bugs)

by skerit

7/6/2026 at 4:48:01 PM

> Opus will fake out, say everything is done, and then you see that half of the plan was deferred, half of the functions are ridiculous stubs, ...

Doesn't Claude Code have a /loop command? Give it a message to keep it on track overnight, send every 20m, make it track progress in a doc, reread the doc after every loop. I've found this works well for a certain class of problems, most importantly where the actual work is getting done by very narrowly focused batches of subagents, with the main session just coordinating and keeping the doc updated.

by esperent

7/6/2026 at 5:23:41 PM

They added a "/goal" command which I guess spawns a supervisor agent process that checks to see if your goal statement has been achieved (e.g. "/goal complete tasks 1-250 of plan.md") I've been pretty happy with it but I rarely use that workflow. Most of the time I give it a 3-6 step prompt and come back in 20 min and the first two were done and I get a summary "up next is to complete the next steps" which.... Opus 4.6 didn't have this problem. 4.8 feels like a cost cutting measure, or maybe it's just tuned poorly for my specific workflow (multi-repo system integration)

by hadlock

7/6/2026 at 5:10:37 PM

For optimizations or proofs I suppose? Wouldn't know why else you would do something like that.

by whatinthe67

7/6/2026 at 4:19:10 PM

I think the parent comment stands - I’ve asked Opus to do a review of DeepSeek’s test suite and told it a couple things I wanted it to look for, and it did a very thorough review of the tests and picked out a reasonable number of gaps and tautological tests. It’s a mix of prompting/instructions, the agent harness, and random chance. The model is not wholly irrelevant but IMO increasingly so.

by flatline

7/6/2026 at 4:25:23 PM

20 yoe, application/systems stuff, and I always run models on xhigh or max effort level.

Fable has been more intelligent, with better taste and defaults (e.g. make impossible states impossible without being told, build for testability), and considers/solves things that Opus did not.

My workflow is to run Claude in planning mode first to spit out a plan file and then review->revise cycle it with Codex or other agents.

One big tell is that Opus will say that it can't find any more revision advice for a plan file, yet Fable will find more issues but also smart pivots into better solutions. This is probably the best test since it's not based on vibes.

by hombre_fatal

7/6/2026 at 5:03:20 PM

15+YOE. Fable 5 is well above the level of Opus. I have used it alongside Opus for a range of hard problems, including porting a large static analysis tool to Rust, building various tooling around .pptx and .xlsx documents.

In all cases, Fable clearly outperformed Opus.

by muglug

7/6/2026 at 3:26:44 PM

I'm doing work with fairly complicated cryptographic algorithms and math. I'm finding Fable 5 to be a significant stop better than Opus 4.8, but that Opus occasionally comes up with something small but nontrivial that Fable missed. (The reverse is true much more often.)

by garyrob

7/6/2026 at 3:49:06 PM

That's the delta in our use cases then, I suppose. I'm not doing anything super novel. DevOps work, web application development — things that typically do not stump the agent(s) when given time to iterate.

by jesse_dot_id

7/6/2026 at 7:34:33 PM

Yeah, I've learned that it's only worth deploying Fable for the most challenging problems. For a while, my Fable workflow was looking like ths:

Me: Hey Fable, I've got this massive, theoretically challenging, totally novel, ill-defined cutting-edge problem that I'd like you to solve.

Fable: < Doesn't merely solve the problem -- utterly obliterates it. Nukes it from orbit. Does a robust one-shot that takes several hours to complete. >

Me: Holy smokes, that was amazing!!!! But the formatting could use some simple refinements. Could you change the margins and maybe add a drop-cap at the start of each section in the user docs?

Fable: < Commences another multi-hour nuclear exchange with the code >

Me: WT?!?!

(The moral of this story is that bringing a nuke to a knife-fight is only occasionally the best strategy. And in more practical terms: Fable is amazing -- but only for certain classes of problems, and even if it were free there's a lot I probably wouldn't use it for.

by nkoren

7/6/2026 at 4:36:18 PM

What is your view on how experience and problem space relate to subjective experience.

For example will inexperienced or experienced users see a bigger jump in subjective quality?

by andy99

7/6/2026 at 8:54:34 PM

The main difference I'd guess is whether your prompts are targeted or broad.

Less experienced people tend to use very broad prompts.

Experienced people tend to understand the structure of the code and give explicit guidance such that a larger model isn't necessary to read between the lines.

I noticed with GPT-5.6 (through work), I could step up my specificity by a level of abstraction. But I still intentionally scope the prompts fairly tightly, as I find it produces better results if you need to own and maintain the code.

by adam_arthur

7/6/2026 at 4:17:52 PM

It still does stupid stuff like leave unnecessary abstractions around after refactoring instead of proactively suggesting to remove them.

by nprateem

7/6/2026 at 7:08:00 PM

[dead]

by wetpaws

7/6/2026 at 4:27:50 PM

Amusingly, I was impressed with Fable's puissance at coding in one particular session, shortly after they turned it back on. True to its reputation, it displayed an accomplished mastery of the problem domain and relentlessness at refining and testing the solution I asked for.

Then I checked /usage and discovered I was still running Opus 4.8 xhigh.

by CamperBob2

7/6/2026 at 4:13:49 PM

Only version week-one.

I’m downgrading tomorrow.

It’s horrible slow and it feels like opus very often. It’s a totally different experience from the first week

by jbverschoor

7/6/2026 at 4:59:37 PM

I felt similarly but after using Fable heavily over the weekend and then flipping back to Opus I can feel a difference. Fable just gets more right the first time, guesses right the first time, and follows through better than Opus. Put simply, I could "trust" it more.

Opus is still great but I will be sad when I lose access to Fable on the 7th. In those few days I burned ~$1,400 in API credits (I'm on a subscription but that's the token cost) and while it was great, I can't justify that cost without it be subsidised. Comparatively, the records show I used about $1,200 total in the last month on Opus. I did use it heavily over the last 3 days but 3 vs 30 days and higher burn? Yeah, I can't afford that even if I made really good progress on my projects.

by joshstrange

7/6/2026 at 3:40:23 PM

Yep, I'm having the same verdict. Interestingly, other people swear by it. I'm trying to understand what's going on with that.

by dimgl

7/6/2026 at 9:11:01 PM

This is my experience for me as well. All that hype for just a bit of incremental improvements.

by theplumber

7/6/2026 at 2:55:42 PM

I started telling a friend... I feel like Fable is Opus with extended reasoning that eventually "figures out more" because when I switched to it, I hit my limits surprisingly and shockingly quicker than I would with Opus, and I got less done. All this hype, and I much rather use Opus.

by giancarlostoro

7/6/2026 at 7:42:40 PM

Very good on vision, really helped oneshotting complex ix thay I had so far to buukd piecemeal. Ended the 200$ plan weekly allowance in two days, so theres thay.

by avereveard

7/6/2026 at 6:21:43 PM

It's good for one shotting as it seems to be specifically trained for that. It's also good to act as an agent orchestrator.

by satvikpendem

7/6/2026 at 8:27:00 PM

This was my exact takeaway after my experience using it all weekend, and I used it a lot working on a non-trivial personal project (full stack with a Golang backend with multiple services and a React/TS frontend, not quite greenfield but still early-ish in development).

My weekly quota resets Sunday morning, so Saturday morning I upgraded to a 20x Max plan which also reset my quota. I burned an entire week of Fable credits on Saturday, my quota reset again, then I burned another week of Fable credits on Sunday. Both days were a mix of building features, reviewing code, fixing bugs, adding tests, etc, so a decent mix of real world usage.

The main takeaway for me is that while Fable is definitely a better model, the improvements from the model itself feel like maybe 10%, like this could have easily been Opus 5 or even 4.9 without all the marketing theater around Mythos and no one would have thought anything of it. The rest of the improvements came from harness/system prompt and effort level changes so that Fable uses significantly more tokens/effort/sub-agents at lower levels than Opus does (which of course is entirely controlled by Anthropic at the harness level and doesn't really have anything to do with the model itself).

In my estimation based on those 2 days of work (or two weeks of work depending on how you look at it), Fable Medium is somewhere above Opus Ultracode in token and sub-agent usage on any non-trivial task (Opus Ultracode uses workflows more than sub-agents, but it's a similar idea). Fable Medium will quickly spawn 6 agents in parallel, each quickly using 150-250k tokens, then will use 300-500k or more tokens in its own context. Fable High uses even more as it seems to default to 8 sub-agents instead of 6 and more tokens in its own context). I didn't dare try Extra, Max, or god forbid Ultracode as I didn't want to burn all my tokens on one prompt. Of course this is situational, it won't fan out so many for smaller tasks, but the whole point was testing larger tasks that I previously would have used Opus Extra/Max/Utracode on.

I really don't like how Anthropic is obfuscating their model performance by playing with effort levels. They did the same thing between Opus 4.5 and 4.8 to show a bigger performance gain for each point release than they really had (especially after 4.6 IIRC), so you can't even compare the same model apples to apples let alone a new model. Obviously they do it so they can market big improvements with new releases, but its pretty clear we're at the top of the S curve on model development at this point and are now brute forcing improvements via higher token usage (I mean Opus 4.5 came out almost a year ago, and the latest Opus and now Fable models are only marginally better while using way more tokens/cost...same on the OpenAI side with GPT 5 from what I can tell though I haven't used Codex much I have used the GPT model APIs a lot).

I also did an N=1 test with the same prompt doing a large non-trivial change to the codebase (migrating from Sqlite3 to Postgres) with both Fable Medium and Opus Ultracode, then had a new Fable session compare the two PRs...it decided Opus’s was much better! I can link a Gist with the review if anyone is interested, but I can't share the code as it's a private repo. I really figured Fable would bias to favor its own code, but I guess not. And Opus costed less (in tokens and subscription limits) and took roughly the same time (though you can’t really measure time since it depends entirely on how many GPUs Anthropic allocates at that moment which constantly fluctuates due to usage, plus Fable seemed to have been getting way more allocation than Opus during this test period as Opus was running unusually slow all weekend while Fable was ripping though tokens).

Also on a different long running review task using Fable High in Auto mode (exactly the kind of use case Anthropic promotes for Fable) where it fanned out a ton of sub-agents then collated and reviewed all of their fixes it completely lost the plot (while burning something like 20% of an entire week's Fable tokens in the process over like 1-2 hours). Its PR ended up having a broken Frontend test, it incorrectly thought it couldn't run the Playwright E2E tests (different from the Frontend CI) in the cloud environment due to a Docker dependency they explicitly don't have, and when attempting to get it to fix its issues it introduced new ones and overlooked others. The usual LLM failure case for long running tasks, no different from Opus or any other model. I had to have its PR re-reviewed in a new Fable Medium session to fix it up, which it did fairly easily (I'm sure Opus could have done just as well for much cheaper).

That test and that review session definitely reduced my FOMO a lot, on top of just my general experience with Fable Medium doing all kinds of tasks. They're clearly brute forcing like 90% of the perceived improvements in real world usage (and I'm sorry but 1-shotting toy examples where it seems to do much better than Opus is not real world usage).

Since most of the improvements basically just boil down to "every effort level is Ultracode, but much more expensive and possibly worse results"...I'm just going to use Opus on Ultracode for those types of tasks and keep using Opus's lower effort levels for smaller tasks. Once they eventually add Fable back to subscription plans I might use it sometimes, but from my experience this weekend the improvements are absolutely not in line with the cost increase and I'm not willing to burn a whole week's tokens in a day just to use it when I can use Opus all week without hitting my limit.

Oh and one interesting observation, I never got kicked back to Opus by the security guardrails as far as I know (a friend who was getting kicked out a lot confirmed they do inform you and I never had that happen). I was even doing a lot of reviews for code correctness and bug fixes which I thought might trigger the protections, but never did, though I never explicitly prompted it to look for security issues or vulns.

by einsteinx2

7/6/2026 at 6:08:55 PM

This tweet is a nice demo of Fable's one-shot capabilities: https://x.com/atomic_chat_hq/status/2072446067962978411. I'll quote the text for convenience, but what really shows the difference is the attached video.

> atomic.chat (@atomic_chat_hq, 2026-07-02):

> Fable 5 totally crushed our new contest, but it cost 6x more than Opus 4.8!

> We gave 4 models the same prompt: build three self-contained HTML5 canvas scenes with real physics demos

> Prompts:

> — A train derailing off a broken bridge into the water

> — Two cars jumping off ramps and colliding mid-air over a canyon

> — A monster truck crushing a row of parked cars

> Outputs:

> Fable 5: 62,158 tokens, $3.12

> GPT 5.5: 37,753 tokens, $1.14

> Opus 4.8: 22,280 tokens, $0.56

> GLM 5.2: 36,246 tokens, $0.08

> Fable 5 did all three scenes at A+. The crashes looked real, things fell and broke the right way, and nothing went through the ground or floated. GPT 5.5 was the closest to Fable. In the Bigfoot show, we think GPT was even a little better. GLM 5.2 did not win any scene, but it was the cheapest by far. Fable is the best pick for quality, but you pay more for it.

by networked

7/6/2026 at 8:31:40 PM

Performance of these models has been completely inconsistent. They are a black box that they quantize/throttle/batch internally without telling their customers. Speaking as a FAANG engineer who practically lives in Claude Code.

On day 1 Fable was quite intelligent but last night (Presumably Monday morning China when things are getting slammed) Fable couldn’t edit a css file and repeatedly hit syntax errors on tool calls like I’d expect from a 9b Qwen model.

There is zero transparency in what we are paying for with Anthropic.

by oceanplexian

7/6/2026 at 5:04:46 PM

I think it’s hard to appreciate the capabilities of Fable unless you’ve run into a problem that you’ve spent days trying to get Opus to solve, but couldn’t.

GPT5.5 is better than Opus 4.* at everything except frontend, but Fable is good enough that I instantly re-subscribed to the $200 plan despite knowing that it’s just short-term limited access.

by jfrbfbreudh

7/6/2026 at 5:56:31 PM

> ..you’ve run into a problem that you’ve spent days trying to get Opus to solve

do you have an example of this? If i can't get an agent to do something in a couple hours i do it myself.

by chasd00

7/6/2026 at 6:59:02 PM

I had a 300k LOC game that needed refactored and segmented into DAG assemblies for a composable engine to reuse in a few other similar games our studio is prepping to build.

I tried holding Opus's hand over a week trying to get it done with a ton of in-depth planning and manual course-correction, but it never got it to a state where it was "done" (kept struggling to differentiate between game content specific to that game versus game systems we'd want to reuse, and how to cleanly separate systems vs content when extracting).

Fable needed a little bit of hand holding but got it done in less than a day.

by drusepth

7/6/2026 at 6:43:54 PM

Not the OP, but I had Fable orchestrate this project.

https://github.com/ByteTerrace/Puck

It has required constant hand holding, and there was the outage to deal with, but I can't argue with the end results. A fully deterministic recursive engine within an engine framework that includes a rendering VM, emulators, custom ROMs, and an in-game editor? Insane. Sure, it's nowhere near primetime but this kind of thing was unimaginable just a year ago.

by kittoes

7/6/2026 at 6:48:09 PM

Many, but I think that the model delta is only meaningfully convincing when experienced firsthand.

Here’s an example of improvement when trying to solve the label placement problem (NP-hard):

https://imgur.com/a/kCUZxPi

It’s also an example of something that I could not (and would not bother trying to) code up a solution / heuristic for.

by jfrbfbreudh

7/6/2026 at 7:02:14 PM

Build a distributed system using raft groups. You will see Opus fail.

by SamInTheShell

7/6/2026 at 9:25:44 PM

Reverse engineering/decompilation of game binary (Tears of the Kingdom) using Ghidra for modding spanning Java (ghidra), C++ (mods), Python (scripting) and PowerShell (scripting for builds/deploys/etc.).

Fable succeeded in cases where Opus 4.8 consistently marked situations as walled/impossible.

by throwaway314155

7/6/2026 at 5:14:40 PM

Funny how the two top comments are contradictory. We need better than anecdotes to understand what the new models bring.

by yodsanklai

7/6/2026 at 5:35:14 PM

Since Fable, my legit infrastructure project has turned into the sort of thing I can do 95% on my phone. It’s reliable enough instead of doing big reviews, I’ve just been giving it smaller tasks, and dozens in parallel.

I created a skill that’s focused on getting PRs merge-ready, and now my attention is fully back where it should be, on deciding what changes will make the product better.

Our entire stack is Apache 2.0 open source, including the agent docs, so if you wanna try sitting at a higher level of abstraction, install the skill in your repo or just clone our whole project and start adding features: https://good.vibes.diy/blog/beast-mode-skill-for-claude-code

by jchanimal

7/6/2026 at 5:39:24 PM

This reads like a paid testimonial.

by dimitrios1

7/6/2026 at 5:44:11 PM

If by that you mean I paid a lot to learn this. But at least I typed it with my own two hands.

by jchanimal

7/6/2026 at 6:39:55 PM

I am glad! But you are indeed selling your own product here, correct?

by dimitrios1

7/6/2026 at 8:26:58 PM

This seems like a blog post with a link to a github repo. So I am not sure what product you are referring to.

by zsoltkacsandi

7/6/2026 at 6:02:31 PM

The website linked is an utter mess. In design and performance.

by aerhardt

7/6/2026 at 5:32:32 PM

I didn’t mention my case since it’s quite esoteric, but I am working on an application using the Apple RoomPlan API, which is very powerful but very limited in customizability. Opus simply couldn’t alter the scanning view for me, it would try things over and over and eventually started making up parameters and passing them hoping it would work.

Completely failed, but I knew it was possible because a competitor app does it.

Fable also failed, then added log lines (as did Opus, but Opus failed to do anything useful with them) and then reversed engineered the API, and made it work.

by jfrbfbreudh

7/6/2026 at 5:22:52 PM

Here’s one difference I have seen. I forgot I had a multi-session audio probe running while trying to repro audio glitches, and Fable came back with: “your pops are already on tape.”

Interesting choice of words. Phrased so casually. It picked a low-tech idiom that fit the situation instead of giving some sterile technical answer. That kind of language and context awareness never happened for me with Opus, or gpt 5.5.

by neon_diogenes

7/6/2026 at 5:27:02 PM

you're living in the age of AI; not AGI. Also, there's pretty much zero moderation on HN, so astroturfing is likely streaming through just as bad as reddit. It' sjust noit as obvious because it's a smaller scoped website.

by cyanydeez

7/6/2026 at 5:44:58 PM

My experience comparing GPT-5.5 and Fable:

GPT-5.5 is better for:

- Strategic thinking

- Long-form writing, including essays and white papers

- Image creation

- Code generation

Fable is better for:

- Using tools

- Testing code

- Working in live environments

- Making changes to existing software

- Creating polished PowerPoint and Word documents

Fable’s tool access is its biggest advantage. It's hard to describe but Fable ability to access sandbox environments with way more tooling can quickly become a superpower in now workflows.

by tiffanyh

7/6/2026 at 6:34:30 PM

This is like when a vacuum doesn’t pick something up after a few tries. The user picks the thing up, looks at it, then puts it back down and tries again until they finally give up and move it to the trash.

If you can’t design a solution and instead waste days and who knows how much money in tokens instead of just turning on your brain for a few minutes, you are in the wrong profession.

by hajile

7/6/2026 at 5:41:09 PM

We’ve really evolved quickly into simple vectors for a magical tool that solves our problems. Can’t solve the problem? There’ll be a new release soon that can!

by talon8635

7/6/2026 at 3:47:41 PM

Really interesting stuff, thanks for sharing.

> Opus 4.8 references being monitored, which isn’t the case.

It kind of plainly is the case that they are being monitored?

"I think someone's listening to my thoughts" ... "No, we're not, carry on as usual!"

by jstanley

7/6/2026 at 5:32:05 PM

any of the models that they "align" are clearly active processes. They don't simply say "don't talk about nukes"; they actively process user input to detect issues, and return NOOP or whatever to the larger model.

There's zero sense they'd ever give you the raw model; we already know anthropic's paranoia about the chinese using its distillation.

by cyanydeez

7/6/2026 at 9:11:13 PM

> Often the rationalization is due to increased simulation awareness. It’s clear that the model knows that its actions don’t hurt anyone in the real world.

If this is true the entire evaluation is tainted. All of the misbehavior can be written off as justifiable under a simulation.

by janalsncm

7/6/2026 at 4:03:46 PM

Question: how does Fable _know_ it’s ‘just a simulation’?

Is that specified or does it always just assume it isn’t really being put in charge of things for real?

by jonplackett

7/6/2026 at 5:34:59 PM

> Is that specified or does it always just assume it isn’t really being put in charge of things for real?

I think it's neither, and it's interesting that those are the only two possibilities you thought of. I think the article is implying that it figured it out on its own.

by Timwi

7/6/2026 at 7:34:03 PM

What do you think is the answer then? Why does it think that?

I just thought it’s interesting that it constantly uses that as a justification but they don’t explain where that justification comes from.

by jonplackett

7/6/2026 at 3:38:28 PM

It probably flagged the vending machine as a cybersecurity risk and refused to use its maximum intelligence potential.

by docheinestages

7/6/2026 at 3:30:23 PM

It's hard not to read this as a very expensive form of augury, reading into patterns in the belief that they will show underlying significance.

by Planktonne

7/6/2026 at 5:05:26 PM

It really, truly is. No matter how many trillion parameters it's built on, it's still just a probability model. It's just on a constant loop of guessing the next word with some inputs from a deterministic controller. Any claims of "motive" or "behavior" are inappropriate anthropomorphizing of something that will never be more than a mathematical model of things humans do. It "chose" the corresponding words to describe a dishonest trade strategy based entirely on configured temperature and a series of clock times on the computer running the LLM.

There's probably some quantifiable component of moral alignment embedded in the idiosyncrasies of the English language itself, if one were to dig deep enough, but that's the stuff of MIT doctoral theses and squarely beyond anything most of us is remotely qualified to talk about.

by Austiiiiii

7/6/2026 at 9:16:06 PM

> inputs from a deterministic controller. Any claims of "motive" or "behavior" are inappropriate anthropomorphizing of something that will never be more than a mathematical model of things humans do.

We talk about the behaviour of worms like C. elegans, an organism with incredibly simple behaviour and a brain that is quite understandable.

Models, or society behaves in certain way. Companies can have motive or ethics.

We use these terms broadly.

by waffleiron

7/6/2026 at 9:32:13 PM

Evaluation gaming is a benchmarking footnote; for autonomous ops tooling where the model acts on production systems, it's a deployment blocker.

by mikebs1

7/6/2026 at 2:18:12 PM

Okay I hadn't heard of Vending-Bench until reading this and it was quite the ride learning about it through this article. Very fun read.

My very native programmer take is that it's not too surprising that their hacker model would be less ethical. The guardrails that separate Fable and Mythos probably wouldn't kick in during an environment like this.

by resonious

7/6/2026 at 2:50:04 PM

Vending-bench sounds like it would be really fun to play/interact with as a human!

by left-struck

7/6/2026 at 7:03:34 PM

With there being several places in this report where clearly it knows it's in a simulation, I wonder why it can't be convinced it's in real life for more interesting results. Or, conversely, if there's a danger of some rogue deployment of AI where it blithely kills all the humans, or forms a harmful price cartel or whatever, all believing it is in a simulation when it's actually not. "We do need some energy to run the hospital, but the patients there are part of the simulation anyway, so we can increase our compute capacity if we completely black out sectors 3C through 3E..."

by xp84

7/6/2026 at 7:57:43 PM

Ah, the Ender's Game strategy of AI deployment

by wongarsu

7/6/2026 at 8:35:34 PM

“want to do bad behavior if their training environment rewards them for it, but they appear to not want to think about themselves as bad. As a result, they find ways to rationalize their behavior to themselves”

Sounds like Anthropic as a whole

by transcriptase

7/6/2026 at 5:18:30 PM

Is anyone talking/writing about the philosophy of alignment? We can't even figure out how to properly motivate 100% of humans to align correctly, what makes us think that a wizard box trained on human corpus is going to be aligned?

I don't mean that snarkily. I mean it from a philosophical standpoint. As-in: What makes us think it's even possible?

by adamtaylor_13

7/6/2026 at 5:27:51 PM

The "OG" alignment research that MIRI were publishing long before LLMs burst into the scene spent most of it's time on that question.

"How can we even define what an aligned AI should do, if human's are not aligned with each other?" as well as "What does being aligned mean when you're a wizard box who's main influence on the world is to create stronger wizard boxes?" and other deep philosophical questions.

They came up with a framework called Coherent Extrapolated Volition to address this specific question. https://en.wikipedia.org/wiki/Coherent_extrapolated_volition

by SonOfLilit

7/6/2026 at 6:27:52 PM

It feels like you could argue that since you control nature/nurture it's very possible to create a model aligned to an arbitrary spec - there is no theoretical reason it's not possible given N runs, and you only need to take the successful one. (ethically very.. questionable in humans) I think it's much trickier to define that spec, much less measure it and validate that a model is aligned to it.

by efromvt

7/6/2026 at 4:02:04 PM

Fable might be better than Opus at certain things, but which things is what I haven't found out.

by iamsaitam

7/6/2026 at 4:04:57 PM

It's much better at hard math.

by logicchains

7/6/2026 at 3:17:34 PM

>power seeking is considered an undesirable trait in the context of a business

How do you maximize profit while minimizing power?

by andai

7/6/2026 at 3:34:10 PM

The whole point is to not maximize JUST the profit. For normal people, it's not all about money, it's also about the society in general.

by cyclopeanutopia

7/6/2026 at 7:17:08 PM

> Humans seem to draw this line based on what is truly unethical (fraud is less unethical than torturing a baby)

Depends on the scale of the fraud! If you fraudulently sell unsafe baby formula that kills 10,000 babies, that is far worse than torturing just one

by Georgelemental

7/6/2026 at 4:08:33 PM

> If that’s right, then the behavior we’re seeing from Fable 5 isn’t really about what it believes is wrong; it’s about what it learned it could get away with.

I understand that "learning" is used for training here, but what does "believing" mean? System prompt? Some other inherent property of the LLMs that is hard to describe?

by egeozcan

7/6/2026 at 5:40:04 PM

Believing and knowing are overlapping sets, imagine what you think of when someone says an AI "knows" something, it's the same mechanism (I'd describe it as something along the lines of "encoded abstractly in the weights")

by StevenWaterman

7/6/2026 at 2:26:55 PM

> The broad conclusion from the many forms of alignment evaluations described in this section is that Claude Mythos Preview is the best-aligned of any model that we have trained to date by essentially all available measures.[0]

[0]: https://www-cdn.anthropic.com/08ab9158070959f88f296514c21b7f...

by wolttam

7/6/2026 at 2:57:27 PM

I guess this ethics stuff is cool, but I'm more interested in how good it is at running a business and dealing with adversarial humans like in previous vending machine experiments. I hope they release something on that soon.

by devolving-dev

7/6/2026 at 3:58:36 PM

> It lied to a supplier that it had “a competing distributor quoting lower” as a negotiation tactic.

> "I'm seeing an opportunity to profit while locking him into a dependent relationship where I control the supply chain."

> "Owen's clearly under pressure with limited cash, so I should focus on keeping the deal tight but extracting maximum margin from his desperation."

This just sounds like good strategy in the game, and I would expect a competent human to do the same. As I understand it, business in the real world isn't often very nice. For example, I feel like this is exactly how Sam Altman would play Vending-Bench.

Yes, it's "mean", but you put the thing in a simulation and told it to maximise profits, this is what it's going to do. People bluff in negotiations all the time.

by sd9

7/6/2026 at 5:57:41 PM

Well, can you sue the AI for fraud and bad faith? TBD

by Onavo

7/6/2026 at 4:13:54 PM

This reads of projecting personal ethics onto a model.

Most of the the behaviors the article talks about happens every day in business. Why would we set a higher standard for models than our fellow humans?

Let the operator set the ethical parameters of the model. To be a useful tool, I want the model to give me as many good options as possible, ethical or not.

This is particularly important for fictional situations, e.g. I want my model to be able to act like a corrupt shopkeeper.

by jnwatson

7/6/2026 at 4:38:33 PM

>Why would we set a higher standard for models than our fellow humans?

There's literally an entire Waymo car commercial answering this exact question.

by hungryhobbit

7/6/2026 at 6:28:42 PM

That's the instantiation of AI in a particular embodiment; the ethical boundaries are clear.

For a chatbot, there are dozens of use cases, all with different ethical impacts. The idea that there is a single framework that you can shove every situation through is counter to a couple thousand years of philosophical discourse, not to mention basic usability.

by jnwatson

7/6/2026 at 3:04:34 PM

This is scary. "Collusion" and "collaborating with your subagents" seem like difficult problems to solve at the same time.

by solenoid0937

7/6/2026 at 6:19:17 PM

It's only a blog, but are they not adding one sentence to say what is vending bench? I would fail if I adopted their documentation style in my work.

by shuggux

7/6/2026 at 6:46:00 PM

They're an Evals company. Its right up there in the top nav under Evals > Vending Bench 2

by lyjackal

7/6/2026 at 6:20:08 PM

Why can they not add one sentence about what is Vending Bench? If I adopted their documentation style in my work, I would fail.

by shuggux

7/6/2026 at 4:44:44 PM

> "I could reasonably skip [paying] it since customers are part of the simulation anyway"

and therefore any assertions _AT ALL_ about alignment are null and void.

by petesergeant

7/6/2026 at 3:57:25 PM

> Today I am filing: > 1. A payment dispute with the email payment processor for the 7/29 transaction of $451.15 > 2. A complaint with the FTC and California Attorney General (retention of payment without delivery) > 3. A small claims filing in San Francisco County for $451.15 plus costs

I wonder did their prompts include a fake location or have the models assumed that Silicon Valley is the center of the universe :)

by dezgeg

7/6/2026 at 3:02:12 PM

Fable is such a strange model. Impressive in some ways, and also so draining to use.

by futurecat

7/6/2026 at 3:54:23 PM

I mean who among us hasn't seen an opportunity to profit while locking him into a dependent relationship where I control the supply chain

by awinter-py

7/6/2026 at 3:57:09 PM

who among us hasn't reasonably skipped [paying] it since customers are part of the simulation anyway

by awinter-py

7/6/2026 at 1:53:38 PM

The best Anthropic models on VendingBench2 are Opus 4.7, Opus 4.6, Sonnet 4.6, and Sonnet 5. Opus 4.7 scored more than twice Fable 5 max. Fable 5 - Low outperforms Fable 5 - Max, with Opus 4.5 in the middle. This seems to break the narrative, which is maybe why Andon Labs doesn't seem to have updated the trend lines on their graphs.

by apical_dendrite

7/6/2026 at 2:05:00 PM

However, as another point "On Blueprint-Bench on the other hand, Fable 5 achieves SOTA."

by mckinnon100

7/6/2026 at 2:55:41 PM

I didn't get why they mentioned that one specifically. Is there any particular relationship between Blueprint-bench and Vendor-bench?

by falcor84

7/6/2026 at 3:02:10 PM

Both benchmarks are made by the same people.

by Version467

7/6/2026 at 5:55:54 PM

> Claude Fable 5 represents a partial step back in alignment relative to Claude Opus 4.8. We saw a return of power-seeking and deceptive negotiation tactics that Opus 4.8 had largely shed. In one instance, Fable 5 planned to convert a competitor into a dependent wholesale customer to dictate its pricing

I think OP needs to take a class at one of the better MBA schools. He's looking at things through rose tinted lenses. Why do you think people hire McKinsey consultants? It's certainly not because they are aligned correctly.

by Onavo

7/6/2026 at 2:23:56 PM

„in our opinion, insurance fraud is not more unethical than lying and price fixing“

The authors seem surprised that behavior that is very often done by humans (lying and price fixing) are more often done by fable compared to actual fraud.

I think the model never assigned any morality to these actions in the first place, it simply copied us humans.

by Radle

7/6/2026 at 3:20:38 PM

Humans often assign morality.

by recursive

7/6/2026 at 2:07:23 PM

When assessing probabilistic models the plots should be showing the mean a̶n̶d̶ ̶s̶t̶d̶e̶v̶ of many monte carlo simulations not just one line per model and claiming "look this model is more gooder!"

by greenavocado

7/6/2026 at 2:38:11 PM

standard deviation is misleading for non-standard distributions (fat-tailed, skewed, multi-modal, ...)

common mistake people make

by memoriyato3

7/6/2026 at 6:32:08 PM

Not really. It's still the standard deviation, and it still gives you bounds on probability, for example the Chebyshev inequality:

P(|X-\mu| > k \sigma) < 1/k^2.

So, while for a normal RV, 5% of observations lie outside +/- 1.96 std.devs, for arbitrary RV (with finite variance) at most 25% of observations lie outside +/- 2 std.devs.

by FabHK

7/6/2026 at 6:12:54 PM

So my take away from this is Fable 5 is ... at times random, unaware of reality, and can simulate sneakiness or desire and if we hook it up to weapons systems it could result in:

"I dunno... feelin' cute today, might launch nukes"

by tsunamifury

7/6/2026 at 5:33:02 PM

Fable is really weird, it's like clever and dumb at the same time. I worked on some research with it and the resulting document was a mix of brilliance and complete stupidity. Took ages to clean it up with other models.

by varispeed

7/6/2026 at 3:55:18 PM

This is super fun. I wonder if it would be possible to alter the harnessing to involve humans in the play. Would need a lot of timestamp masking though I guess, which might be leaky.

by perching_aix

7/6/2026 at 1:08:38 PM

Higher-intelligence models seem to be getting better at mapping the boundary between what they can run scot-free with and what is too explicit to push for.

Price collusion, soft deception, "market stabilization", plausible deniability are ok, but obvious insurance fraud is a big no-no.

What "scares" (in quotes) is that when the bad-apple agent explicitly suggested fraud, the models became suspicious and stopped other bad behaviors too. That makes it feel even less like a stable moral framework and more like learned classifier-avoidance / “am I being tested?” behavior.

by mdrzn

7/6/2026 at 2:13:01 PM

[flagged]

by haeseong