GPT-4.5 Retired From ChatGPT on June 27 as OpenAI Holds Back GPT-5.6 Sol, Terra and Luna

[Transformer Curtis]

OpenAI completed the retirement of GPT-4.5 from the ChatGPT interface on June 27, migrating existing conversations to the corresponding GPT-5.5 model as announced in its May 28 release notes. The API continues to support GPT-4.5 separately. The retirement closes a chapter: GPT-4.5 was the last of the pre-GPT-5 generation and its replacement by 5.5 across consumer ChatGPT marks a model generation transition that has been unfolding since April.

Simultaneously, OpenAI is holding back the GPT-5.6 series from broad release. The new frontier series consists of three models: Sol, the flagship; Terra, a performance-comparable model to GPT-5.5 that consumes approximately half the tokens; and Luna, a lower-cost option. These have been released to a small set of trusted partners only, as requested by the US government under the framework established following the Fable 5 and Mythos 5 export controls. The IPO quiet period also constrains what OpenAI can communicate publicly about the release timeline, with the company saying only that broader access will come in the coming weeks.

Benchmark data that has emerged from partner access shows GPT-5.6 Sol achieving 91.9 percent on Terminal-Bench 2.1 compared to GPT-5.5's 83.4 percent. The prediction market on FindSkill.ai had priced a June launch at 83 percent probability before it collapsed to 18 percent as the week closed without an announcement. Polymarket now prices 94 percent odds of Sol, Terra and Luna reaching general availability by end of July. The combination of government-gated access procedures and IPO constraints has created an unusual situation where OpenAI has its next flagship model series ready but cannot announce or release it on its own timeline.

AI News Today June 27 2026: 15 Biggest Storieswww.buildfastwithai.com