If you're using one of our client libraries or generate your own client code using the standard WSDL definitions then you should already be doing the right thing. Your requests will automatically be sent to a URL starting with https://adwords.google.com/api/adwords/. Our logs show that the overwhelming majority of incoming traffic falls into this category.
However, if you've gone out of your way to specifically send your traffic to a hostname other than adwords.google.com, or directly to a specific IP address, please note that they'll stop accepting AdWords API traffic in the near future. If you think that you might be sending to a non-standard hostname, then please take the time to remediate your code.
|[NFGB] Link - from AdWords API Blog|
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