--- title: Fable 5 vs. GPT-5.6 Sol on an NP-Hard Problem: Does... description: A hands-on benchmark comparing Claude Fable 5 and GPT-5.6 Sol on an unpublished NP-hard fiber-network optimization problem (KIRO), with and without each tool's... canonical: https://daily.dev/posts/fable-5-vs-gpt-5-6-sol-on-an-np-hard-problem-does-goal-help--fdnctyoir twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Fable 5 vs. GPT-5.6 Sol on an NP-Hard Problem: Does /goal Help? | daily.dev og:description: A hands-on benchmark comparing Claude Fable 5 and GPT-5.6 Sol on an unpublished NP-hard fiber-network optimization problem (KIRO), with and without each tool's... og:url: https://daily.dev/posts/fable-5-vs-gpt-5-6-sol-on-an-np-hard-problem-does-goal-help--fdnctyoir og:image: https://api.daily.dev/og/posts/FdNCtyoIr.png og:image:alt: Fable 5 vs. GPT-5.6 Sol on an NP-Hard Problem: Does /goal Help? og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Fable 5 vs. GPT-5.6 Sol on an NP-Hard Problem: Does /goal Help? **[Hacker News](https://daily.dev/sources/hn)** · 7 min read · 1 upvotes · 0 comments ## Summary A hands-on benchmark comparing Claude Fable 5 and GPT-5.6 Sol on an unpublished NP-hard fiber-network optimization problem (KIRO), with and without each tool's native /goal mode. Fable 5 outperformed Sol significantly — lower scores, tighter variance, and a best overall result of 31,934. The /goal feature won 4 of 6 individual trials but made average performance worse for both models due to occasional large regressions when a bad solver strategy was amplified by extra time. The post also digs into the fundamentally different /goal implementations: Claude Code uses a separate Haiku evaluator that reads only the transcript, while Codex CLI persists goal state in SQLite and lets the working model self-assess with tool access. The key takeaway is that a persistence loop can win most trials while degrading mean performance — what matters is the quality of what the loop keeps doing, not the loop itself. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [GPT-5.6 Sol vs Claude Fable 5: Which Model Writes Better Plans?](https://daily.dev/posts/gpt-5-6-sol-vs-claude-fable-5-which-model-writes-better-plans--m7odzpdq7) · Kilo Blog · 1 upvotes · 0 comments - [Grok 4.5 vs Claude Fable 5 vs GPT-5.6 Sol: How I’m Testing Them Across 100 Real Tasks](https://daily.dev/posts/grok-4-5-vs-claude-fable-5-vs-gpt-5-6-sol-how-i-m-testing-them-across-100-real-tasks-hb5pgi2wo) · Medium · 0 upvotes · 0 comments --- Tags: [#ai-coding](https://daily.dev/tags/ai-coding), [#claude](https://daily.dev/tags/claude), [#gpt](https://daily.dev/tags/gpt) [View this post on daily.dev](https://daily.dev/posts/fable-5-vs-gpt-5-6-sol-on-an-np-hard-problem-does-goal-help--fdnctyoir) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Fable 5 vs. GPT-5.6 Sol on an NP-Hard Problem: Does /goal Help?","url":"https://daily.dev/posts/fable-5-vs-gpt-5-6-sol-on-an-np-hard-problem-does-goal-help--fdnctyoir","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/fable-5-vs-gpt-5-6-sol-on-an-np-hard-problem-does-goal-help--fdnctyoir"},"datePublished":"2026-07-18T12:54:35.099Z","dateModified":"2026-07-19T04:25:51.495Z","description":"A hands-on benchmark comparing Claude Fable 5 and GPT-5.6 Sol on an unpublished NP-hard fiber-network optimization problem (KIRO), with and without each tool's...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/28c7143b6c8a23cf632f9847d8945fb7?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/28c7143b6c8a23cf632f9847d8945fb7?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Hacker News","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Hacker News","logo":"https://media.daily.dev/image/upload/t_logo,f_auto/v1/logos/hn","url":"https://daily.dev/sources/hn"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/fable-5-vs-gpt-5-6-sol-on-an-np-hard-problem-does-goal-help--fdnctyoir","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":1},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"ai-coding,claude,gpt","timeRequired":"PT7M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Hacker News","item":"https://daily.dev/sources/hn"},{"@type":"ListItem","position":3,"name":"Fable 5 vs. GPT-5.6 Sol on an NP-Hard Problem: Does /goal Help?"}]} ```