I'm founder of the OpenCage geocoder, we'll gladly work with anyone large or small, we have clients doing millions of requests per day. We use OpenStreetMap but also other open geo data sets. https://geocoder.opencagedata.com
One thing our app needs is a way to only get street address matches. Basically, I already know that an address is a street address or at least a very small side road. It's not an entire county or city, and never a very long road like a highway. Google lets me filter out such bogus results by returning a "bounds" field in the results. Using this bounding box I can calculate the area, and ignore anything less than 200x200m, regardless of the type of feature returned (which is sometimes a "route" even though it's very small). I see your API returns a "bounds" in the results, but it's not documented. Is that what it's for?
I'm also looking for a good autocompleter. Basically, if my app is about Montana, then the user should be able to type "M" and get "Missoula" as the top hit within 50ms. Not Mississippi or Montreal or anything outside Montana. It should also be possible to misspell names, type partial street addresses and so on. Google's geocoding API is useless for this since it doesn't do fuzzy matching. They have an API called Google Places, but it has restrictions and doesn't seem designed exactly for this stuff.
We don't offer an autocomplete.
Places API autocomplete can be limited to only return results of type 'geocode', which will give you the autocomplete of just geocodable locations, and was designed for this purpose.
[1] https://developers.google.com/maps/documentation/geocoding/i...
Generally, the geocoder's substring matching has limited range, which is why it is fairly useless for autocompletion. Its partial matching seems limited to misspellings or nearly-complete terms. For example, I just tried typing "mead", and asked the API for 10 results. I got 5 results, all things like "Mead Lane" or "Meade Ave", but no "Meadowood". So it stopped at 5 even though there are more sharing that prefix. If I type "mea", I get just _one_ match, about some random place with "Mea" in the name. In other words, it's doing something else (something more sophisticated, but less appropriate for this use case) than mere prefix/substring matching.
Again, it's been a while, but from the last time I looked, I recall the Places API being better for this type of incremental autocompletion, but it had some issues related to geofencing that made it almost as bad.