As previously 
announced on the AdWords blog, we're improving how 
exact and 
phrase keywords match to users' search terms. Starting in late September, all phrase and exact match keywords will begin matching 
close variants, including misspellings, singular/plural forms, stemmings, accents, acronyms and abbreviations.
Specifically to the API, this means the following:
- The next API version will no longer accept KeywordMatchSetting for campaigns.
- Existing API versions will ignore the value sent for the optInfield of KeywordMatchSetting.
- Regardless of the optInfield value, all exact and phrase match keywords will match close variants.
Close variant matching is already enabled by default for new campaigns, so if you haven't specifically set the 
optIn field, you won't see any changes in keyword matching behavior.
If you have any questions, please feel free to contact us on 
the forum or via the 
Google Plus page.
 - Danial Klimkin, AdWords API Team.
 - Danial Klimkin, AdWords API Team.