Fable 5 vs. GPT-5.6 Sol on an NP-Hard Problem: Does /goal help? • Hacker News Board

Re: Fable 5 vs. GPT-5.6 Sol on an NP-Hard Problem: Does /goal help?

#101

Post by drivebyhooting » Sat, Jul 18, 2026, 9:10 PM UTC

embedding-shape wrote: post #6

o10449366 wrote: post #4

/goal has replaced plan mode for me. This is the pattern I use for 95% of my AI work now: 1. Read X feature of Y and tell me when you fully understand it (if there's any detail missing in the summary, repeat until the context is primed) 2. What time is it? 3. /goal Spend X minutes from $time writing a technical design doc on $feature. There must not be any vague language or ambiguity in the document. Read carry_forwa…

> 3. /goal Spend X minutes from $time writing a technical design doc on $feature. Hmm, I feel like this is akin to making a recursive function have a exit condition not based on what it actually did/found, but based on how long time it took. I'm always using /goal with explicit goals that the agent needs to achieve. Time-bounding them wouldn't make sense, I want something specific done regardless of how long time it…

The proof prompts do say to spend at least 8 hours.

Re: Fable 5 vs. GPT-5.6 Sol on an NP-Hard Problem: Does /goal help?

#102

Post by kingkongjaffa » Sat, Jul 18, 2026, 9:15 PM UTC

Huppie wrote: post #75

alexpotato wrote: post #73

Earlier quoted context omitted.

> But, for many tasks, ultra mode is possibly worse and certainly more expensive. Went through something similar. Fable would just spends minutes thinking, processing, confabulating etc. I dropped down to Haiku and got an answer in >30 seconds.

Simon Willison recently had a useful tip instructing Claude to use its judgement to pick an appropriate model for tasks. After a short discussion about the idea with Claude mostly on how it fits in my workflow and what models / effort I would like for certain tasks it placed a paragraph in my global Claude.md and it has worked wonders. Ultra became a lot better (faster, cheaper for the same output) and the amount of…

How does it change model mid conversation?

Does it spawn sub agents with different models or is it the same single conversation dynamically switching models?

Re: Fable 5 vs. GPT-5.6 Sol on an NP-Hard Problem: Does /goal help?

#103

Post by demosthanos » Sat, Jul 18, 2026, 9:22 PM UTC

robwwilliams wrote: post #56

IceDane wrote: post #22

Earlier quoted context omitted.

Stop using compaction. Stop treating sessions as something you keep alive for weeks. Set up a proper workflow for handing off work and start handing off well before maximum context is hit. It's less efficient, slower and more costly to constantly be sitting at high context and compaction is just not good.

There is no one-size-fits-all, even for programming.

There isn't, but everything that they said above is absolutely true and people who try to fight it will suffer. There is lots of flexibility within those constraints, but the constraints aren't imaginary.

Re: Fable 5 vs. GPT-5.6 Sol on an NP-Hard Problem: Does /goal help?

#104

Post by 9dev » Sat, Jul 18, 2026, 9:50 PM UTC

mh- wrote: post #94

9dev wrote: post #52

Earlier quoted context omitted.

I'm way too afraid of a "paperclip problem"-style target overfitting to use it really; how could I even describe a goal so well it doesn't sacrifice other things that are important to me? Like, if my goal is to make an endpoint faster, will it create an over-engineered mess out of the clearly readable code I have to reach that goal?

/goal open a draft PR that makes ~200ms faster while still passing tests, and adhering to nearby style+pattern It's obviously not perfect, but it's not like you're going to YOLO it into prod without evaluating it on whatever you care about. If you want to be able to use it like that, you need to find a way to encode (most of) your concerns into something that can be programmatically verified.

That kind of emphasises the problem I was referring to; if I pick 200ms, will it stop before doing a proper optimisation because that would make it faster than that? Will it do something stupid to justify pushing from 195ms to >=200ms?

Re: Fable 5 vs. GPT-5.6 Sol on an NP-Hard Problem: Does /goal help?

#105

Post by mh- » Sat, Jul 18, 2026, 9:52 PM UTC

9dev wrote: post #104

mh- wrote: post #94

Earlier quoted context omitted.

/goal open a draft PR that makes ~200ms faster while still passing tests, and adhering to nearby style+pattern It's obviously not perfect, but it's not like you're going to YOLO it into prod without evaluating it on whatever you care about. If you want to be able to use it like that, you need to find a way to encode (most of) your concerns into something that can be programmatically verified.

That kind of emphasises the problem I was referring to; if I pick 200ms, will it stop before doing a proper optimisation because that would make it faster than that? Will it do something stupid to justify pushing from 195ms to >=200ms?

It might! In my prompt, I'm supposing you have some priors here about what's possible. Try saying something like "materially faster". But you need to also make sure it knows how to measure that endpoint's performance on its own, otherwise I wouldn't expect this to work well at all.

Re: Fable 5 vs. GPT-5.6 Sol on an NP-Hard Problem: Does /goal help?

#106

Post by throwaway314155 » Sat, Jul 18, 2026, 9:55 PM UTC

gmac wrote: post #59

sreekanth850 wrote: post #58

Anthropic is losing bigtime against Open AI in coding space. I was using Claude code upto last march. Not an enterprise customer, but a responsible AI user where i don't over spend and use basic plan to manage repository with 400Kloc all together. We sell to local government and a team of 3. Claude code was super slow, never able to fix issues properly.(Despite with proper test cases, observability, documentation and…

I've found Opus 4.8 pretty amazing, and Codex a bit meh. YMMV?

My only issue with Codex (Sol 5.6) is that it sometimes finds tasks on its own to solve that are definitely out of scope. like it’s always aiming for the 1.0 release when we’re still on 0.1.0a

Re: Fable 5 vs. GPT-5.6 Sol on an NP-Hard Problem: Does /goal help?

#107

Post by tpicks » Sat, Jul 18, 2026, 10:27 PM UTC

lambda wrote: post #67

tantalor wrote: post #10

What is /goal?

The article describes it. Both Codex and Claude Code have it, but they work slightly differently. Claude Code uses Haiku to read through the transcript and decide if the goal has been completed. If not, Haiku injects a prompt back to the main model to indicate what still needs to be done. In Codex, instead it's a tool available to the main model, plus some part of the surrounding harness that will re-prompt it if the…

> Claude Code uses Haiku to read through the transcript and decide if the goal has been completed.

feels kinda odd to use a less capable model to determine if the goal is fully complete. Especially if the user is expecting /goal to thoroughly complete the task. A less capable model would be more likely to misclassify `isComplete?`

Re: Fable 5 vs. GPT-5.6 Sol on an NP-Hard Problem: Does /goal help?

#108

Post by rubyn00bie » Sat, Jul 18, 2026, 11:56 PM UTC

sreekanth850 wrote: post #58

Anthropic is losing bigtime against Open AI in coding space. I was using Claude code upto last march. Not an enterprise customer, but a responsible AI user where i don't over spend and use basic plan to manage repository with 400Kloc all together. We sell to local government and a team of 3. Claude code was super slow, never able to fix issues properly.(Despite with proper test cases, observability, documentation and…

I think it depends on the problem space, and to a large extent the languages used. I have had the opposite experience with GPT.

I have found GPT to be pretty awful at writing Elixir, and dealing with more open ended tasks. Opus is (for the moment) better at writing Elixir, and Fable is much better than either at actually grokking a problem space. I had switched to GPT for about six weeks and eventually stopped using it altogether after it relentlessly gaslight me. Those six weeks using it were essentially completely wasted work.

Right now I’ve moved to a mix of Opus/Fable and Deepseek Pro. Deepseek is far and away the most cost effective, fast, and quite good for 90% of implementation work. Deepseek really only falls apart (in Elixir) when it tries to use runtime features at compile time; which, for the initial lift of a project I have was a bit painful. Fable was able to pretty quickly get things sorted and now things are progressing nicely.

With all that said, I think the various models have unique strengths that are sometime hard to uncover. I also don’t see a world, at least in the near future, where I’ll only use one model. I’m happy Anthropic continues to push the frontier forward. I’m more than happy to trade “efficiency” for quality when I need to.

Re: Fable 5 vs. GPT-5.6 Sol on an NP-Hard Problem: Does /goal help?

#109

Post by what-the-grump » Sat, Jul 18, 2026, 11:59 PM UTC

jswny wrote: post #19

Tenoke wrote: post #17

Claude seems to forget what you tell it in very long work sessions (things that take weeks to develop), no matter how many times you tell it which part is extra important. I dont use goal (I guess I should), but presumably it makes it actually remember the most important instruction. I believe this here is about shorter sessions where the issue doesn't crop up as much.

Unfortunately I’ve used Claude and GPT models for a long time in a variety of harnesses and I agree with you and I think it’s the compaction. For some reason, codex compaction is like black magic. I’ve never felt like I can just one one continuous thread with other models, Claude I carefully curate when I compact

Pretty much, I stopped using Claude for that reason, I shouldn't have to keep track of the context of the model all the time. And god forbid I don't, the amount of time I've lost to Claude just sending it and then lying is not worth it when 5.5 will just do stuff, compact 2-3 times in the task and still not go insane.

This whole 1 million context window is a lie after 300k Claude degrades to unusable, and compact doesnt help. I've had Codex tabs open for weeks, I have to regularly restart Claude.

Re: Fable 5 vs. GPT-5.6 Sol on an NP-Hard Problem: Does /goal help?

#110

Post by stevenhuang » Sun, Jul 19, 2026, 12:13 AM UTC

robwwilliams wrote: post #56

IceDane wrote: post #22

Earlier quoted context omitted.

Stop using compaction. Stop treating sessions as something you keep alive for weeks. Set up a proper workflow for handing off work and start handing off well before maximum context is hit. It's less efficient, slower and more costly to constantly be sitting at high context and compaction is just not good.

There is no one-size-fits-all, even for programming.

If you want to use LLMs effectively, everything OP said is true. It has been this way since the beginning. There will be a time when long context and compaction will be effective, but now isn't it.