Revision History

Update: GPT-6 Sol and Luna released Sept 22 as successors to GPT-5.6 Sol and Luna; no-GPT-6-variants sentences dated

Link Claude Fable 5.1 and Claude Mythos 5.1 to their new pages

Correction: GPT-5.6 Sol's API price has been a promotional $4/$20 per million tokens since August 21, 2026 (the article said its launch rates were unchanged); adds the September 3, 2026 GPT-6 Astra launch as successor, with OpenAI's Sol-versus-Astra benchmark and alignment comparison, pricing ratio, and Aidan Clark's training-run statements

Add the August 13 GPT-5.6 Sol Ultrafast limited preview, distinguish it from Standard and Fast API processing, and qualify vendor speed and latency claims.

Add Astra: OpenAI confirmed its next major model family on August 1, 2026; ship name (GPT-6 or otherwise) undecided.

Correction: the prompt cache TTL is a fixed 30 minutes rather than a minimum, and Simon Willison's cost comparison used his SVG-drawing prompt rather than an image-generation request

Add the July 30, 2026 API price cut: Luna 80 percent lower ($1.00/$6.00 to $0.20/$1.20 per 1M tokens) and Terra 20 percent lower ($2.50/$15.00 to $2.00/$12.00), Sol unchanged. New Price cut subsection with before/after table, unchanged long-context, cache-write, Batch/Flex and rate-limit rules, Fast mode replacing Priority Processing, OpenAI stated serving-cost rationale, and a verified DeepSeek V4-Flash price comparison. Dated the pre-cut Artificial Analysis, ARC Prize and Willison cost figures as launch-price measurements.

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