# The builder’s guide to GPT‑5.6

GPT-5.6 Luna matches GPT-5.5's BrowseComp score for $1.33 versus $33.27, and new API settings triple ARC-AGI-3 scores.

- GPT-5.6 Sol at "low" reasoning outperforms GPT-5.5 at "high" reasoning on Agents' Last Exam.
- New Responses API primitives: persisted reasoning, native compaction, multi-agent orchestration, and programmatic tool calling.
- Prompt cache TTL extended to a minimum of 30 minutes with deterministic cache breakpoints.
- Hypha reports Luna keeps 98% of GPT-5.5's extraction accuracy at one-eighteenth the cost.

## Why it matters

Startups building agents can now get frontier-level performance at a fraction of the cost, changing the economics of agentic workflows.

## Sources

- [OpenAI: The builder’s guide to GPT‑5.6](https://openai.com/index/builders-guide-to-gpt-5-6)

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Summarized by dstilled on 2026-08-13. https://dstilled.ai/story/b5f932af-333f-4e18-8d82-e56374285e89