Setting aside the comments about nerfing, do normal mortals out there have workflows that really require Fable/Mythos and don't just work fine on Opus 5.5?

I've been using Opus 5.5 on xhigh for some decently aggressive software development on a ~125k-line project, and it has been fine for me. I'm not really willing to dive into a "rewrite the whole project, don't make any mistakes" level of refactoring. I'm not looking to try to prove Fermat's Last Theorem myself. Is there anything that I'm truly missing?

Yes, more intelligent models enable new workflows. We'll discover them in the coming weeks.

I have some intermediate level Db Optimization skills for slow rails requests that I can point fable at and get a PR at the end after 30-45 minutes.

Opus 5.5 very frequently gets into rabbit holes and imagined edge cases which I have to intervene and tell it to ignore. It ends up taking longer and costing more tokens. It also very frequently requires me to agree on how to move forward multiple times, whereas fable just drafts the PR and tells me its ready. I have steering included in the skills to avoid some of this but Ive seen these same patterns frequently in regular opus 5.5 use in other areas as well

I'm cleaning up old, unintuitive code that is badly architected all day long. The previous developers used stupid patterns and bad naming schemes and created tons of unnecessary complexity. Everything is so interconnected that it’s like defusing a bomb when trying to refactor... Yeah, I feel I’m nowhere near where I would want to be in terms of capabilities, even with Opus 5.5.

But the improvements in how well the model does the work are noticeably better with every good model release. As of now, orchestration of agent pipelines is ALMOST so good that I can point it at a problem, and it will solve it safely and reliably without making a mess. But it requires an agent pipeline with context gathering, refactoring, attack sessions, a sprinkle of Sol 6.1 for bug hunting, and Sol 6.0 for Daybrak security audits, and a final de-bloat/clean up pass. I’m feeling that we’re getting close to doing a lot of the work fully agentically. But I can absolutely "feel" that we are not there yet when it comes to the intelligence I need. I need moar!

I’ve found that Fable is good when the model intuition really matters. For instance, picking model architecture in a machine learning problem. Opus will grind the implementation just fine, but having intuition for picking a good research direction is better with fable

I am in the exact same boat as you. Opus 5.5 on High solves all engineering problems i encounter in my SWE job. If it doesnt do well, its nearly always requirements engineering: I did forget to specify something or there was a misunderstanding. Or taste approach wrt to architectures chosen. None of these are really different if I use a stronger model.

I am also happy with this current state, as I believe it will at some point allow me to transition to open models once they reach the level of opus 5.5. high. But its probably futile to try predict the future in these times.

On my 100 person engineering team's monorepo, every model is better at better at detecting subtle bugs as it works -- reliability goes up and thus I'm further moving faster. (Most of my work is brownfield style refactoring).

LoC doesn't tell full story.

It could be flat web app with frontend -> api -> db later, or some very complicated system with many components and edge cases. Imo, in second case, Opus still have lots of struggle to understand system as a whole.

> do normal mortals out there have workflows that really require Fable/Mythos and don't just work fine on Opus 5.5?

I usually have Fable review what Opus produces. The edits are almost always valuable. For complex or high-stakes work, too, I'll have Fable review and revise my prompt before passing it to Opus and Sonnet swarms.

As said in other comments, when dealing with a not perfect codebase, a smarter model can be really helpful. A smarter model is also better at understanding intentions in the prompts. Some of my tasks require a big detailed prompt but finding the assumptions is really demanding (for me), so a smarter model helps.

I only use Fable 5.1 when I'm able to start on a larger feature within my work's codebase. Most tasks can be done by Sonnet 5.5 or Opus 5.5 so I don't fret, especially if I understand the technical aspect of what's being done, e.g. user's dashboard gets a new button to do X thing, error happened b/c we didn't catch it the first time around.

For Fable, I really like to think of it as the heavyweight reviewer whenever I'm about to start so I save myself some security and/or glaring technical issue.

Sure but they’re the harder problems.

Eg. https://tfmbot.com is an implementation of a popular board game. Opus and even sonnet handle that part. Each week i spend my remaining credits on fable to think how to improve the ai opponents. It plays at a very high level (can get into the top 100 on BGA if i let it). Opus alone couldn’t get it to the level it’s reached.

Opus 5.5 still makes mistakes all the time even if the prompt isn't super complex. A stronger model make mistakes less often, thus wasting less of my time.

If you understand your problem well and know 80-90% what you want it to look like (or it just isn't very hard), it's just more cost effective to use a smaller model. Even Opus is overkill for a lot of the work I do. Most code I produce is from Luna Max implementing against fairly prescriptive plans made by bigger models.

I have been using Luna at work and I am very happy. It can take care of keep doing all the hard grunt work. Other models keep stopping too soon.

I barely have work that needs more than Qwen 3.8 Flash Next needs. Opus 5.5 and Sol 6.1 are already way more than enough at work for me.

I’m in the same boat. Though I will occasionally use Fable to review things to see if it can pick up anything but I’ve honestly not found it to be any more effective than Opus.