Bot API 429s during JMeter load test for AI conversations

Does anyone understand why the Bot API endpoints are throwing 429 Too Many Requests errors during a moderate concurrency load test?
I am running a JMeter 5.6.2 script from Singapore to simulate inbound AI conversations, but the /api/v2/bots endpoint starts rejecting requests at 100 concurrent threads even though the rate limit header suggests higher capacity. Any known thresholds for v2.0 bot interactions?