Here's an updated table, with version numbers included and their status:
Gemini Models gemini.google.com
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Gemini 1.0 Nano
Gemini 1.0 Pro -> Gemini (free)
Gemini 1.0 Ultra -> Gemini Advanced ($20/month)
Gemini 1.5 Pro -> announced on 2024-02-15 [1]
Gemini 1.5 Ultra -> no public announcements (assuming it's coming)
For history of pre-Gemini models at Google, see: https://news.ycombinator.com/item?id=39304441