xAI: Grok 4 Fast

curl https://api.x.ai/v1/chat/completions \
  -H "Authorization: Bearer $XAI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "grok-4-fast",
    "messages": [
      { "role": "user", "content": "Summarize the latest product changes in three bullets." }
    ]
  }'

Verify the exact model identifier in the provider docs before production use. ai-tracker stores canonical ids and pricing snapshots, not account entitlements.