Upstage serves its Solar models at https://api.upstage.ai/v1 with an OpenAI-compatible chat API. Solar is especially strong in Korean.
Create a key at console.upstage.ai. Send it as Authorization: Bearer <key>. In the examples it's written {{UPSTAGE_API_KEY}}.
Full reference: https://console.upstage.ai/docs/getting-started
curl https://api.upstage.ai/v1/chat/completions \
-H "Authorization: Bearer {{UPSTAGE_API_KEY}}" \
-H "Content-Type: application/json" \
-d '{"model": "solar-pro4", "messages": [{"role": "user", "content": "Explain what an API rate limit is in two sentences."}]}'
curl https://api.upstage.ai/v1/models \
-H "Authorization: Bearer {{UPSTAGE_API_KEY}}"