I have seen more 429, almost all from large cloud providers, a fair amount in the last 5 years. Never before then, I was used to making rate limiting an in-band

I have seen more 429, almost all from large cloud providers, a fair amount in the last 5 years. Never before then, I was used to making rate limiting an in-band part of the API explicitly. AWS S3 will give you 429s before giving you 503s when you hit it with a go program touching every object or every version in a giant bucket from a 56 core machine and a few hundred Go routine workers. It is a good signal: if you do exponential back off per worker on the 429s, you won’t see the 503s.