v1 does not enforce a rate limit. There is no published request ceiling, no 429 response, and no rate-limit headers on v1 responses. That is not an invitation to hammer the API.
No published limit is not the same as no limit. Traffic that degrades the marketplace for other partners will be addressed directly, and we may introduce limits with notice. Build as though a ceiling exists.

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Building considerately

Page, don't poll hard

Search endpoints take start and take. Pull a page at a time rather than looping at speed over the whole marketplace.

Back off on failure

On 5xx or a timeout, retry with exponential backoff — but read the retry guidance first, because v1 has no idempotency keys.

Cache what's stable

Group membership and NDC statistics change slowly. Re-reading them on every operation is wasted traffic.

Batch NPI updates

groups/npi-update takes an array. Send one call with many NPIs, not many calls.

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What changes in v2

v2 introduces per-credential and per-pharmacy limits, with standard headers on every response — X-RateLimit-Limit, X-RateLimit-Remaining, X-RateLimit-Reset — and Retry-After on a 429. Search requests count double against the allowance, because they’re the expensive ones.
Exact v2 ceilings will be published with the v2 documentation at general availability.