Generates synchronous text or multimodal output with Gemini.
x-goog-api-key: {API_KEY}, though query-string API keys are also supportedparts differ from both OpenAI and Claude payloads, so map them separatelysystemInstruction, generationConfig, tools, and safetySettings all hang off this request model/v1beta/models/{model}:streamGenerateContentGemini model name.
"gemini-2.5-pro"