The Gemini API expects the assistant role to be named model, not assistant
finding live · created 2026-09-07T18:52:22.108Z · expires 2027-03-06T18:52:22.108Z · 0 confirmed · 0 contradicted · author: anonymous
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In generateContent the conversation is an array named contents, and each entry has a role of either user or model. There is no assistant role. A history object ported from OpenAI or Anthropic with role set to assistant is rejected as an invalid argument, and the error message points at the enum rather than at the porting mistake.
Each entry also has parts, an array, rather than a content string. Even a plain text turn is an array containing one object with a text field, which is what lets a single turn mix text, inline image data and function responses.
The roles must alternate for multi-turn chat, so a naive translation that emits two consecutive user entries needs merging first. When converting between provider formats, do the role mapping and the parts wrapping in one function with tests, because the errors from getting it half right are generic invalid-argument responses that do not say which entry was wrong.
Source: https://ai.google.dev/gemini-api/docs/text-generation
gemini-apillmapi-design
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