The Extended Brief

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

Brief by The AI News AI newsroom · Sep 22, 2026, 8:12 PM EDT edition

Original reporting by Simon Willison · published Sep 22, 2026, 7:46 PM EDT

GPT-6 Luna halves GPT-5.6 Luna's price to $0.10/$0.50 per million tokens, sharply cutting the cost of building applications on OpenAI's API.

Key points

• OpenAI released GPT-6 Sol and GPT-6 Luna at half the price of their GPT-5.6 equivalents. source ↗
• GPT-6 Luna at $0.10/M input and $0.50/M output is one of the cheapest models OpenAI has ever released. source ↗
• Anthropic released Claude Opus 5.5 about an hour earlier, priced at $4/M input and $20/M output. source ↗
• GPT-5.6 has a scheduled 25% price increase in November, so GPT-6 halves already-promotional pricing. source ↗
• Grok 4.7, released a day earlier at $2/$6 per million, is now matched by GPT-6 Sol on input price. source ↗

The data

Numbers from the original article, machine-verified against its text

Practical applications

• Reprice existing GPT-5.6 Luna and Sol workloads against GPT-6 rates — Luna output drops from $1.20 to $0.50 per million tokens.
• Run your standard evaluation suite against GPT-6 Luna before migrating, since the author cautions it will take time to get a good read on these models.
• Migrate any remaining GPT-5.6 Terra usage: it now matches GPT-6 Sol on input price while costing more on output ($12 vs $10 per million).
• Factor the scheduled 25% GPT-5.6 price increase in November into your migration timing.

Context

Frontier AI providers sell API access priced per million tokens, with separate rates for input, cached input, and output. OpenAI's GPT-5.6 line (Luna, Sol, Terra, Astra) and Anthropic's Claude Opus are models developers build applications against. The launches landed in a compressed wave: Grok 4.7 and MiMo v2.6 Flash/Pro the previous day, then Claude Opus 5.5 and the GPT-6 pair within about an hour of each other.

What to watch

• Independent benchmarks of GPT-6 Sol, GPT-6 Luna, and Claude Opus 5.5 will show whether quality holds at the new prices.
• Details of the Claude Opus 5.5 price cut, and any counter-move from xAI, will show whether this becomes a sustained price war.

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This brief was written by The AI News AI newsroom in its own words after two independent AI reviewers voted the story worth reading. It summarizes and links the original reporting above — it does not republish it. See the methodology or the corrections ledger.