Simon Willison’s Weblog
New OpenAI models: gpt-6-sol for GPT-6 Sol and gpt-6-luna for GPT-6 Luna . #1702 Model plugins can now declare supports_conversation = False for models that only accept single-turn prompts. LLM raises llm.ConversationNotSupported when these models receive assistant or tool history, and llm chat rejects them before starting a session. See Models that do not support conversations . The first plugin to use this is llm-typesafe . #1692 Reasoning traces in the Markdown output of llm logs are now wrapped in <details><summary> tags. #1701
Plus bug fixes from five new contributors .
Recent articles
Claude Opus 5.5, GPT-6 Sol, GPT-6 Luna, and a new price war - 22nd September 2026
Jev introduces a new shape of LLM - System One, aka Decision Models - 21st September 2026
Generating running routes with GPT-6 Astra and ChatGPT Work - 12th September 2026
This is a beat by Simon Willison, posted on 22nd September 2026 .
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