Agent Scripting API 429s during high-concurrency load test

Context:
Running JMeter script to validate agent scripting API throughput. Thread group set to 300 concurrent users hitting PUT /api/v2/agent-scripting/scripts. Environment is Genesys Cloud Production. Seeing 429 Too Many Requests errors after 15 seconds. Rate limit headers indicate 1000 requests per minute window.

Question:
Why does this setting block valid concurrent updates from distinct agent IDs? Is there a global org limit or a per-user token cap I am missing?