OpenAI gives its 2023-2024 models one shared exit: GPT-5.6 Sol takes over on 23 October

OpenAI's deprecation list has quietly become a migration map. The gpt-4-0613 snapshot and the gpt-4 alias, the gpt-4o-2024-05-13 snapshot and the o1 snapshot with its alias all now carry the same shutdown date, 23 October 2026, and the same replacement: gpt-5.6-sol. The o3 snapshots o3-2025-04-16 and o3-pro-2025-06-10 follow on 11 December 2026, alongside the original GPT-5 snapshot. That is a wider sweep than it first looks. GPT-4 is the model that opened the current era in March 2023; GPT-4o carried multimodal chat through 2024; o1 was the first product built around visible reasoning. Three separate ideas about what a model should be are being folded into one endpoint, in which reasoning effort is a parameter rather than a product. The successor is the flagship of the family OpenAI previewed on 26 June 2026 and released on 9 July: three tiers named, least to most capable, Luna, Terra and Sol. Sol answers text and image prompts with text, holds 1,050,000 tokens of context and bills 5 dollars per million input tokens against 30 dollars per million output. On the Artificial Analysis Coding Agent Index 1.1 it scored 80 at maximum reasoning, 2.8 points above Claude Fable 5, while spending under half the output tokens. One detail matters for anyone still on the old models: chatgpt-4o-latest was switched off back on 17 February 2026, so the ChatGPT-flavoured endpoint is already gone even though the dated gpt-4o snapshot survives until October. The distinction between an alias and a snapshot is where migration schedules usually break.