Is the API OpenAI-compatible?

Yes. POST /v1/chat/completions, /v1/audio/speech, /v1/audio/transcriptions and GET /v1/models use the OpenAI request and response shapes, including streaming (stream: true), tools, tool_choice, response_format and usage. The official OpenAI SDKs work by setting base_url to https://api.inferenceapis.com/v1. /openai/v1/… is accepted as well, so Groq-style base URLs need only the host changed. The Responses API (/v1/responses) and embeddings are not yet supported.