[Leynos]

The sort of thing Fable and Sol excel at are long horizon tasks. The sort of thing I have been using them for is migrating large numbers of repositories to new tooling simultaneously (adopting new linters, enabling dependabot automerge, rolling out mutation testing).

Some of that can be done mechanically or trivially, and Fable knows to write a script or deploy Sonnet for those instances, but other times there are complications that need to be overcome that need to be escalated. Then there are patterns that can be picked up in large migrations and fed into template repos or tooling.

I won't use Fable for everything, but if there is ground to be broken on a new concept, being able to build a prototype with Fable might be useful.

I also have some substantive migration tasks such as replacing a static front end with solidjs or moving from NLL to Polonius that I would like to use Fable for.

It certainly feels like over the last fortnight it has enabled a substantial amount of transformative change in my codebases.

[orsorna]

For my needs, Opus does these kind of "long horizon tasks" well enough already, with additional tooling.

As long as you are chunking out the tasks generated from the plan, you can manually (or write an orchestrator to...) give the component tasks to agents that pass along inputs and outputs per the dependency graph derived from the plan.

You can write this plan yourself or review it with the agent. Chunking tasks out of the plan like this has the added benefit of being able to swap for a different model when the time comes (looking forward to Opus-level models I can run on my consumer card...)

Not really convinced using Fable and trusting the harness to orchestrate for you is worth the intelligence upgrade. An understanding of an high level implementation plan of your task is also necessary when working with colleagues who rightfully quiz you. Especially since, at least for my work, there isn't a lot that Opus struggles with.

[LoganDark]

I've been chunking out my plans like this for months, and even maintain a port of Get-Shit-Done https://github.com/LoganDark/get-shit-done to the Jujutsu version control system because that was the best way for me to make the most of Opus.

I don't need that with Fable. I can give Fable a task of any complexity and it will spend over 8 hours in a single turn if it needs to. And then the task will be finished.

For example, Fable is far better at helping me keep that port updated with upstream's agentic pace of development. With Opus I would be spending all day working through each merge step by step. With Fable I can safely nap through it.

I don't know exactly how to communicate that difference other than that Fable just seems to make better decisions more consistently and more reliably to the point where I feel confident trusting it a lot more.

[Leynos]

For normal building work I use Opus to plan and GPT 5.6 Terra to build. The point is, these are not normal constrained building tasks.

Perhaps I should have had more faith in Opus's ability to complete tasks like these, but it just hasn't been my experience to date. Opus and 5.5 work great within constrained user story type tasks, but I just don't have confidence in them to complete a large unbounded task like: "find out why the shared dependabot automerge component isn't working on this one repo, then formulate a strategy to roll it out across these 90 other repos, ensuring that Python, Rust, Typescript, go, sensible, and GitHub actions are all correctly updated. Address any CI failures, codex and codescene review comments in your PRs, then merge on green."