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ChatGPT's core text conversation is **available on all plans including free** at chatgpt.com, with apps for iOS, Android, Windows, and macOS. The model lineup has moved on twice since GPT-5.4 (March 2026): GPT-5.5 became the default generation, and **GPT-5.5 itself is scheduled to retire from ChatGPT, ChatGPT Work, and Codex on all plans on October 14, 2026**. OpenAI is actively rolling out its replacement now—**GPT-6 Sol** for Plus/Pro/Business/Enterprise/Edu and **GPT-6 Luna** for Free/Go (from September 22, 2026)—on top of **GPT-6 Astra**, OpenAI's most capable model, which reached Pro/Enterprise/Business-Premium plans and the API on September 4, 2026.

Available on: Windows macOS iOS Android web API

Verified: 2026-09-28

Sources: https://chatgpt.com, https://chatgpt.com/pricing, https://openai.com/index/introducing-gpt-5-4/, https://openai.com/index/introducing-gpt-5-4-mini-and-nano/, https://community.openai.com/t/introducing-gpt-5-4-mini-and-nano-our-most-capable-small-models-yet/1377015, https://learn.chatgpt.com/docs/models, https://community.openai.com/t/introducing-gpt-6-astra-the-most-intelligent-and-aligned-model-in-the-world/1394703, https://community.openai.com/t/announcing-gpt-6-sol-and-gpt-6-luna-in-the-api-codex-and-chatgpt/1399925