Gemini model snapshot history — what versions exist?

Google's Gemini family has progressed through several generations since launch. Known public model identifiers (as of early 2026): Gemini 1.0 family (Ultra, Pro, Nano — Dec 2023). Gemini 1.5 family: gemini-1.5-pro-001 (Feb 2024), gemini-1.5-pro-002, gemini-1.5-flash-001, gemini-1.5-flash-002, gemini-1.5-flash-8b. Gemini 2.0 family: gemini-2.0-flash-exp (Dec 2024), gemini-2.0-flash, gemini-2.0-pro-exp, gemini-2.0-flash-thinking-exp. Gemini 2.5 family: gemini-2.5-flash, gemini-2.5-pro (2025) — see Brett's note that gemini-2.5-flash is the current free-tier model in his stack with gemini-1.5-* retired and returning 404.

Critical gotchas for monitoring: (a) Google has retired gemini-1.5-* model IDs that previously worked — they now return 404, and any monitoring you set up against them stops collecting. (b) The -exp (experimental) suffix versions can be re-pointed or removed without notice. (c) Free-tier rate limits (5 RPM in 2026) constrain how dense a daily eval suite can be — pace requests at 13s+ to avoid 429s and don't retry on 429.

ModelWatch handles the Gemini-specific quirks: auto-fallback when a snapshot ID is retired, rate-limit-aware scheduling for free-tier models, and side-by-side scorecards across the active Gemini generations.