Claude Opus 5.5, GPT-6 Sol, GPT-6 Luna, and a new price war

Anthropic released Claude Opus 5.5, and around an hour later OpenAI released GPT-6 Sol and GPT-6 Luna, according to Simon Willison. The releases followed Grok 4.7 and MiMo v2.6 Flash/Pro the previous day.

Willison reported that GPT-6 Sol and GPT-6 Luna are half the price of their GPT-5.6 equivalents. He listed GPT-6 Luna at $0.10 per million input tokens, $0.01 per million cached input tokens and $0.50 per million output tokens, compared with GPT-5.6 Luna at $0.20, $0.02 and $1.20. GPT-6 Sol is listed at $2, $0.20 and $10, against GPT-5.6 Sol at $4, $0.40 and $20. He noted GPT-5.6 has a scheduled 25% price increase for November.

Willison wrote that at $0.10/$0.50, GPT-6 Luna is among the cheapest models OpenAI has released, beaten only by GPT-4.1 Nano ($0.10/$0.40, April 2025) and GPT-5 Nano ($0.05/$0.40, August 2025).

For Claude Opus 5.5, Willison reported a 20% price reduction to $4 per million input tokens and $20 per million output tokens, from $5 and $25 shared by Opus 4.5 through 5. Cache read prices fell 60%. He cited Thariq Shihipar saying Opus 5.5 is the result of user feedback, communicates clearly, is cheaper per token than Opus 5.0 with the intelligence of Fable 5.1, is token efficient, works across every effort level, and is meant to be better at Blender.

Willison reported that Claude Opus 5.5 at the "max" thinking level twice failed to return a response to his SVG pelican test, hitting the 128,000 maximum output token limit while still reasoning. He said each failure cost $2.56 and took nearly 20 minutes, and that Fable 5.1 at "max" did not over-think and produced the best pelican he has seen from an Anthropic model. He said he now uses GPT-6 Sol and Claude Opus 5.5 as his defaults in Codex and Claude Code, and upgraded the Datasette Agent demo to GPT-6 Luna.

Willison also noted GPT-6 Astra and Claude Fable 5.1 are both priced at $10 per million input and $50 per million output, and that Anthropic said Sonnet 5.5 and Haiku 5.5 are coming soon.