Rate limits

Requests are limited per API key, and every answer tells you where you stand, so a client can slow down before it is refused.

RateLimit-Limit: 100
RateLimit-Remaining: 97
RateLimit-Reset: 12

Rules

RateLimit-Limit, RateLimit-Remaining and RateLimit-Reset (seconds) come with every answer.
Over the limit, the API answers 429 with type rate_limited, a Retry-After header and error.retry_after in seconds. Wait that long, then retry with the same idempotency key.
The TypeScript SDK retries 429 and 5xx answers for you (2 retries by default, maxRetries to change it), honouring Retry-After.
Each sender also has a sending rate (pacing). The send gate lets a sender send only so many messages a second; a send over it is also refused with 429 rate_limited, Retry-After and error.retry_after, and error.sender names the sender. Retry the same way, with the same idempotency key. The RateLimit-* headers describe only the per-key limit.
New-contact budgets are separate. How many new conversations a sender may start is decided by the send gate (new_contact_limit, sender_throttled), not by these headers.
Use webhooks or the live stream instead of polling GET /v1/events in a tight loop.