FR645 or FR935

Yea, WiFi has been on the spec sheet from the start.

Just to add my 2 cents’ worth, as an alternative to upgrading to the 645 just for the music, you can still pick up Apple iPod Shuffles for around £50. If you attach the EarPods which come with iPhones, it sounds great and you have a useful remote control on the cable. Trust me, it’s so much easier to skip tracks and change volume with this during a run instead of relying on the watch to control Bluetooth headphones.

Also, while both watches may claim to have a thermometer, you really want to buy the Garmin Tempe external thermometer. It’s the same size as the foot pod and it’s way more accurate.

Also, won’t the stainless steel bezel on the 645 degrade the GPS signal which the Fenix 5 suffers from? Has anyone tested the GPS accuracy of the Vivoactive 3 against the 935?

good point - had not thought of that. I can't see any such field as yet however and would be potentially useful for 230/235/630 users although I tend to think if you have a power meter you must already have a device than can read it.

I found one but it seems rather basic and doesn't write to the fit file (and for now doesn't support the 645 yet):

https://apps.garmin.com/en-US/apps/a841dc62-5b25-49ac-b886-e2126bf5a818

My two cents. As a 935 user, I think you should go for the 935. In muy opinion the 645 is too expensive for a watch without the multisports and the less battery.

About the music you can buy very nice headshets with builting MP3 for very few dollars. This option is probably far better that the bluetooth headsets, which usually have problems loosing the music every X seconds when you are running with your bluetooth mp3 player.
And the Garmin pay, honestly it is allways nice to see new features but I don't think that is the most important thing for a running watch.

A previous poster said the 645 is basically the 935 minus multi-sport and 24hr gps battery. I would have to disagree. In my opinion the 645 is a VA3 plus. The looks, design and I'm assuming the hardware are very similar. As a owner of both the 935 and VA3, I would definitely choose the 935 over the 645. Based on the VA3, there are going to be some serious growing pains with the 645. I'm willing to bet battery life will be the biggest issue and the advertised battery life won't come close. The 935 has already outgrown the "terrible two's" stage and has matured into a great device.

TKM17, that's a really interesting perspective. I have money in my pocket right now ready to spend (well, $600 in gift cards from points that i had to redeem). My 735XT has a "spec" battery life of 14hrs. If the 645 non-music lives up to the 16hrs DC Rainmaker says it will have, then i'll buy straight away. If it's more that it struggles to get 12hrs then i'll go with a 935.

My hesitation with the 935 is that there'll be an update mid-year and i'll end up with otherwise great but now a 1/2 cycle behind tech. A smaller, more modern looking watch would be nice. On the other hand, you could wait forever ...

I have the 935 and the wife and I have gone through 3 VA3's. The VA3's were purchased a few months apart in different locations and 1 had to be exchanged. I'm pointing this out so no one assumes our VA3's were from the same lot. All 3 VA3's drop Bluetooth about 50' from my phone. My 935 about 150'. Our VA3's are always dropping the connection on ext HR, tempe, speed and cadence sensors. My 935 will occasionally drop the tempe and I've never had a problem with the other sensors. Clearing the data on all the watches, I've tested how fast I get a GPS fix in front of the house. The 935 is always twice as fast. So, I'm assuming that either the 935 and VA3 are using different hardware, or if the hardware is the same then the design affects the performance. There has been speculation that Garmin devices with the alloy type bezels may cause interference. I'm speculating that the 645 will be using the same hardware just by the looks and design that is extremely similar to the VA3. I'm not trying to talk anyone out of the 645. I think it will end up a great device, just not right away. I'm just commenting on what the OP was asking and explaining why I'd choose the 935. According to Garmin's specs, the VA3 has a battery life up to 13hrs in GPS mode (more like 10) and the 645 non-music 12hrs. I wonder where the 16hrs is coming from?

Disregard that last question. DCR stated that Garmin increased battery life from 12 to 16hrs on the non-music 645 on 01/08/18. You'd think Garmin would update their own website.

One difference I have noticed between these two watches is that on the Connect IQ store the Strava Routes app is available for the 935, but not for 645. There may be other apps that only work with one of them and this could be a factor when choosing between them.
I wonder whether this indicates some hardware difference between these two watches, or is just that the app needs updating to support the 645.

Does anyone have views on whether this app is likely to be available for the 645 in the near future?

the app just needs updating IMO

My guess, is that some apps don't have 645 support for the simple reason that an update with support for the 645 hasn't been uploaded to the store yet. Sometime devs wait until the watch is available (and maybe try it themselves first or find a friend with one) before it's in the store.