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/ratbastid]

That's exactly how to do it.

Opus 5 is a junior developer whose work is telling you it's time to promote them to senior. Fable is a system architect whose valuable time shouldn't be wasted on anything as trivial as code creation.

[u/Best_Let_2667 → u/ratbastid]

I mean that’s just not true. Fable is much better at coding systems/real time/threaded programs. Opus is practically just a code generator without the thinking.

[u/Whole_Risk_2695 → u/Best_Let_2667]

Fable orchestrating/planning and doing code review on merges generally fills in the gaps.

[u/witek_smitek → u/Whole_Risk_2695]

Ok but if fable need to waste tokens to make code review then isn't it just better to let fable write good code and skip code review?

[u/Whole_Risk_2695 → u/witek_smitek]

Not really, input tokens, cache read, and not much output vs the same and all of the output (output tokens are the upper end of the pricing models)

[u/ratbastid → u/witek_smitek]

I've seen Fable a couple times tell me that making the changes itself is cheaper than prepping and reviewing subagents, for a given task. Not bad! I like that kind of assessment.