--- title: "The new GPT-5.6 family: Luna, Terra, Sol" url: https://daily.dev/posts/the-new-gpt-5-6-family-luna-terra-sol-nvvgbeebk source_url: https://simonwillison.net/2026/Jul/9/gpt-5-6 type: article source: "Simon Willison" published: 2026-07-09T19:47:37.374Z updated: 2026-07-10T14:22:02.693Z tags: ["ai-agents", "openai", "gpt"] reading_time: 4 upvotes: 1 comments: 0 language: 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. # The new GPT-5.6 family: Luna, Terra, Sol **[Simon Willison](https://daily.dev/sources/simonwillison)** · 4 min read · 1 upvotes · 0 comments ## Summary OpenAI released GPT-5.6 in three sizes — Luna, Terra, and Sol — with pricing ranging from $1/$6 to $5/$30 per million input/output tokens. The models claim strong agentic performance, with Sol scoring 53.6 on the Agents' Last Exam benchmark, outperforming Claude Fable 5 by 13.1 points. Notably, OpenAI published a critique of SWE-Bench Pro the day before the release, estimating ~30% of its tasks are broken — a benchmark where Fable 5 significantly outperformed GPT-5.6 Sol (80% vs 64.6%). New API features include Programmatic Tool Calling (composing JavaScript to orchestrate tool calls), native multi-agent support, explicit prompt cache breakpoints, and an option to skip image resizing. The author notes GPT-5.6 Sol is competent but hasn't yet surpassed Fable 5 for complex coding tasks in personal use. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: --- Tags: [#ai-agents](https://daily.dev/tags/ai-agents), [#openai](https://daily.dev/tags/openai), [#gpt](https://daily.dev/tags/gpt) [View this post on daily.dev](https://daily.dev/posts/the-new-gpt-5-6-family-luna-terra-sol-nvvgbeebk)