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Gemini Pro → GPT-5

Switching from Google Gemini Pro to OpenAI GPT-5.

Gemini's 1M-token context window is the biggest thing you'll lose moving to GPT-5. If long-document work is core to your product, plan for chunked retrieval and a vector store. Tool-use shape is the OpenAI standard and is what most agent frameworks expect.

Prompt translation tips

  • · Start with your existing system prompt unchanged and run a 20-prompt evaluation set side-by-side; only change what fails.
  • · Watch for instruction-following drift — different labs follow instructions at different temperatures (Anthropic models are stricter).
  • · Tool-call shapes vary — review parallel tool calls, JSON-only output requirements, and any structured-output hints you depend on.
  • · If you use vision, retest your prompt set with the same images — different models excel at different layouts.

Pricing math

Moving from Google: Gemini 2.5 Pro Preview 06-05 to OpenAI: GPT-5:

  • Input tokens: same price.
  • Output tokens: same price.

Capability gaps to plan for

  • · Context window shrinks from 1049K to 400K — plan for chunked retrieval if you load whole documents.
  • · Modalities removed: audio. Affected workflows need an alternative path.
  • · Run your full eval suite against the new model in a Switchy Space before flipping production.

Side-by-side

See the full comparison: Google: Gemini 2.5 Pro Preview 06-05 vs OpenAI: GPT-5.

Other migration paths