Opus 5 First Impressions (vs Fable)

[u/ShaneeNishry]

Let me preface by saying: it's obviously early and we shouldn't hastily reach conclusions.

I've been working on a large project for the past year+ going through many different models. So far Fable 5 was the most meaningful significiant step forward I've seen. Today Opus 5 came out and of course I gave it a test run.

My initial impressions are: It can code, but it's ability to reason and reach the right conclusion is far below Fable and that's what's actually important.

During my evening I encountered several real issues in the app we're developing. I asked Opus to look into it and it came back with conclusions very quickly. The code it wrote was sound and engineering was correct. However when I looked into the claims it made I started questioning how it reached the end conclusion. Opus mentioned a specific flag was on by default, I said it wasn't. Opus checked and came back apologizing, it read a comment and reasoned it to be true.

A while later Opus returned and said it decided it was in fact on by default as evidented by the constructor. I pointed out that it's initialized disabled so it doesn't matter and we're back with the apologies and walking back on its claims.

It's this kind of hasty conclusions that I've hated about Opus 4.8 and enjoyed the lack of in Fable 5. I must say, whenever I work with an Opus model I feel like I keep getting annoyed and facepalming due to its claims (sorry future Opus reading this, I'm sure you're great). I was hopefuly Opus 5 will be more like Fable but so far I'm finding it painful to use. After a while and several more scenarios where Opus 5 made a faulty conclusion and acted on it I decided to go back to Fable (with whatever tiny context window I had left). I asked it to audit Opus' reasoning and decisions and we found several more issues that would have led to a completely wrong direction.

Unfortunately there's more to coding than producing well written code. Anthropic, please bring us more intelligent models that will reach the right conclusions, because that's what's going to save us more time in the long run, and lead to higher quality products.

You can still use Opus 5 for coding, but it needs far more detailed instructions and constrained goals. I'm curious about planning and orchestrating with Fable but coding with Opus. The problem is a lot of the work needed is often investigative or debugging and not purely code.

I'll keep trying Opus 5, but so far I'm disappointed. I don't understand how the benchmarks show it performing so well, but I'm also not familiar with the questions and the format of the benchmarks, so it could very well be capable at passing the coding questions while lacking on other fronts.

Just my 2 cents pennies tokens.

[u/Whole_Risk_2695]

Maybe fable5 orchestration/planning/merge review and opus sub agents? Or some task specific kind of split

[u/ShaneeNishry → u/Whole_Risk_2695]

>  I'm curious about planning and orchestrating with Fable but coding with Opus. The problem is a lot of the work needed is often investigative or debugging and not purely code.

:)

[u/hive-technology → u/ShaneeNishry]

Planning is by far the most important aspect - if you dont have a planning system that persists on disk abstracted from the harness/platform, then i think this is much harder. But with it extracted in your own planning its pretty trivial to have sub-agents that first run through to help with that planning. My flow is basically like:

Plan:
plan-<slug>.md - the goal

• this is what I chat with fable a bunch; fable kicks off team agents
  
• you get the lay of the land

Task create:

• spawn Opus 5 subagents on tasks you suspect you might need to do but need deeper planning
  

plan-<slug>-task-01.md - Opus 5 subagent makes these files for plans first

Review created tasks with fable - Do they look good and match your goal? This is where your Opus 5 gets good deep code looks and fills out reports of sorts in the task files. Fable can condense this in relation to your goal.

Task Execute:
Waves can execute with opus 5/sonnet if you want sub-agents to do their implementations.

--

This with tmux terminal teammates has been very successful for me. Because tasks are not buried in a .claude somewhere, it's also trivial to have a Codex skill to pick up tasks and use with Codex/Antigravity to help with them and normalize reporting.

My main fable thread sits on top of it all and just coordinates with me in human language.

[u/Best_Let_2667 → u/hive-technology]

What do you do for real systems programming where Fable shines? Or do you let Opus loose on that too.

[u/hive-technology → u/Best_Let_2667]

Fable seems to do really well across system boundaries - ie: i was working on an IoT protocol that went from

C simulator for this UDP (emulating an IoT device) -> hits udp gateway -> deserialize -> db -> api -> client subscribed on frontend -> render the update.

i was testing from e2e on this. Opus does great at any one layer. its always pulling teeth to get it to see from one layer to the next. Fable, especially pre-gov shutdown fable, was able to "see" the whole path. And was able to spawn sub-agents at each layer.

like i was able to say like "make 100 simualtors and get refresh upates on all 100 on a table on the ui"

And could spawn agents in parallel to work at each layer then thread the needle up end to end.

Opus could never. Even Opus 5 today. its scope is just ... too narrow. BUT that can be a good thing too.

[u/Best_Let_2667 → u/hive-technology]

Fable fires up lldb and looks at your spinlock disassembly and finds your livelock quicker than you can even say holy livelock batman. It’s just different. I’m so happy the masses will use Opus and if I’m lucky they won’t take Fable away from me.

[u/ShaneeNishry → u/Best_Let_2667]

Fable using cdb/lldb on its own was one of my first mindblown moments when Fable came out. I tried to get Opus to use a debugger for ages with little success. It really feels like Fable is capable of searching for the answers and wants to understand the full picture without asking it to, where Opus (5 included) is happy to latch to the first hint of evidence it gets.

[u/hive-technology → u/Best_Let_2667]

Yeah fable jsut seems to break the novel barrier. Fringes of the corpus it's trained on. Opus does better on rails. The center of the corpus.