/Tech18h ago

Claude Fable 5 Migrates 50M Line Codebase And Generates Complex 3D Graphics

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Deedy@deedydas#370inTech

Claude Fable 5 is by far the most ridiculous model that makes me genuinely afraid for the future of software engineering.

I compiled the top 10 most unbelievable things I've seen Claude Fable 5 do today:

— Migrate a 50M line codebase from Stripe in a day (humans take 2mos) — Draw amazing 3D graphics a) Boeing 747 b) space simulations with >5000 objects c) Minecraft roller coasters d) full photorealistic forest scenes e) NYC skyline f) stormy clouds) — One-shot Pokemon FireRed the game — Optimize a real world proprietary interaction net evaluator 10x more than the next best model, gpt5.5

AND it's about the same price as GPT 5.5 ($10/M input, $45/M output) vs Fable 5 ($10/M input, $50/M output) and 6x cheaper than GPT 5.5 Pro.

6:27 PM · Jun 9, 2026 · 740.6K Views
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Positive users praise Claude Fable 5 for migrating large codebases and generating complex 3D graphics due to impressive productivity gains and pricing, while negative users accuse the claims of being lies or misinformation.

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Deedy@deedydas

Optimize a real world proprietary interaction net evaluator 10x more than the next best model, gpt5.5

Taelin@VictorTaelin

this is my personal singularity moment

this post may sound like a paid ad. I only wish. I'm concerned, more so than happy. the world is changing, and, among the scenarios where AI goes terribly wrong, inequality is the most realistic, yet, the one Anthropic seems to be the least concerned about. I'm glad OpenAI is taking the opposite stance: *personal AGI for everyone*. I think this is a commendable position in the times we live. but who am I in the queue of the bread?

anyway, Fable is here, so I'll just report my first-hour experience

first of all, all my pet prompts are solved. → λ-calculus puzzles → bug questions → one-shot apps all are trivial to it.

I don't have anything harder other than my ongoing work

so, in the last several days, I've been toying with HVM5, a new interaction net evaluator with a faster loop.

after writing the first version, I left 32 GPT-5 agents working for ~20 hours each. this resulted in up to 2x speedups, but the file size increased by 2-fold and quality decreased significantly.

I then simplified the whole thing into an even simpler core, and left Opus 4.8 and GPT 5.5 optimizing it for 8 hours. Opus got a legit 6% - 34% speedup in most benches. GPT got better results, but, sadly, an unusable file.

I then asked Fable to optimize it.

2 hours later, it landed a 1770% speedup in one case, 100%+ in other 4, and 22% in average. yes, in 2 hours it outperformed me, opus 4.8 and a swarm of gpt 5.5 agents, by one order of magnitude.

that could not possibly be legit. "it must be hardcoding the benchmarks" (GPT trauma). so I read its explanation and what it did was, indeed, the most high impact optimization one could try first. seems like HVM5 was wasting a lot of time garbage-collecting unused branches of pattern-match nodes. I had optimized that for static mats, but not for dynamic mats. skill issue. Fable figured how to do it for these, resulting in a massive speedup in some benches

but wait, is that *correct*? I'm not sure yet, it is credible, but this is the kind of thing that is very easy to get wrong on interaction nets. the problem is, when I was ready to start auditing Fable's solution so I could tell whether it was buggy or legit, it interrupted me to tell me it had found a massive bug on the code *I* had written.

... wait, what?

so... for garbage collection purposes, I stored a bit on lambda term pointers that meant "the variable bound by this lambda has been freed, so, its lambda must free whatever argument it is applied to". that's fine. yet, on duplicator nodes, I also used the same bit to mean "one of the duplicated variables was freed, so, treat this dup as a passthrough no-op". so, if a lambda entered a duplicator, it would mistake the lambda's collection bit for its own, resulting in corrupted interaction!

that's a mouthful, why I'm writing this?

just so you can appreciate the sheer absurdity of what just happened. I didn't ask it to find bugs. I asked it for an optimization. and even if I did ask it to find bugs, this bug is so astonishingly subtle and specific, identifying it takes mastering the domain to an extent that it beyond even me. I'd easily need hours or days to fix it, *if* I ever came across it. chances are it would just go unnoticed. and Fable found it and fixed it like it was nothing, while it was busy adding a 17x speedup to a file that neither I, nor Opus 4.8, nor a fleet of GPT 5.5 managed to barely make 2x faster.

oh and there is also another tab where it is also ripping through Bend's codebase and finishing everything I had to do

I don't know what to say anymore

this isn't about Anthropic or OpenAI, this is about our collective future as a species. the world is changing, and we need to be aware of it, and discuss how to handle this change.

receipt below . . .

18hViews 116KLikes 135Bookmarks 61
REPLIES3
Deedy@deedydas

Full photorealistic city storm scene

18hViews 13.6KLikes 15Bookmarks 9
Deedy@deedydas

Minecraft roller coasters

18hViews 13.8KLikes 17Bookmarks 7
Deedy@deedydas

NYC skyline prompt

18hViews 14.3KLikes 16Bookmarks 7
Deedy@deedydas

Stripe code base migration

18hViews 1.8KLikes 11Bookmarks 4
Deedy@deedydas

Boeing 747

18hViews 12.5KLikes 22Bookmarks 2
julian@JulianL093

@deedydas I know you are an investor in Anthropic and Fable is clearly a very strong model, but there's no need to make things up - GPT-5.5 is listed everywhere as $5/M in and $30/M out.

18hViews 1.5KLikes 37
Deedy@deedydas

One-shotting Pokemon FireRed https://www.youtube.com/watch?v=Ty_50J84fMY

18hViews 3KLikes 7Bookmarks 3
Deedy@deedydas

If this is Community Noted, I used the GPT 5.5 / Pro prices on long context, which is far more common for agentic tasks (>272k context).

Anthropic does not discriminate prices on context length.

14hViews 2.4KLikes 4Bookmarks 2
nsxdavid@nsxdavid

@deedydas na dude, it codes okay... but still can't do simple stuff a human can do. None of them can. For example: https://aicrier.com/notes/ais-drag-n-drop-problem

17hViews 652Likes 2Bookmarks 2
Deedy@deedydas

Full photorealistic forest scenes

18hViews 2.2KLikes 3Bookmarks 1
Deedy@deedydas

Space simulations with >5000 objects

18hViews 2.2KLikes 6
Saadat@Saadat87669241

@deedydas Why then does it go through half my tokens when I say hi???

16hViews 1.6KLikes 10
Vasanth G Bhat@careerwitvasant

@deedydas If it's true then it's very good. But, lately I'm fed up of paid posts which says, how these models do this and that and later I ask a simple task, which it will be stuck after a point.

17hViews 1.4KLikes 1Bookmarks 1
Varun tej@itsvaruntej

@deedydas Check this out

17hViews 1.2KBookmarks 1
Aaron Slodov@aphysicist

@deedydas afraid because you can do more?

18hViews 911Likes 8
Seth@seth_codes_

@deedydas Didn’t pass my test bruh

17hViews 437Bookmarks 1
Jatin Garg@jatingargiitk

every item here is visual or self-contained. a 747, a one-shot game, a forest render. those read as real because you can see them work. the one production claim, 50M lines migrated in a day, is the only one that matters and the only one you can't verify from a screenshot. the scary list is the easy 20%.

18hViews 1.2KLikes 2
Larry Pixel@LarryPixel

For some reason, Claude Fable 5 isn’t working for me at all. I’m simply trying to build a medical ERP system, but the model keeps refusing to help and says I’m violating the usage policy. I’m literally just developing standard business software for a pharmaceutical company — inventory, production tracking, sales, and related workflows for medical devices and drugs. Nothing harmful or against the rules. So far this new update feels pretty useless because of these overly strict restrictions.

15hViews 421Likes 2
Aditya Vyas@adityahvyas

@deedydas Deedy is an Investor in Anthropic so I would always take his post for Anthropic with a pinch of Bias.

17hViews 1.3KLikes 1
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