Are we going to see GLONASS Support in the future?

There are hardware differences between GLONASS and GPS receivers. There are also differences between GPS and Galileo, but my understanding is that Galileo compatibility in the receiver chip sets is more widspread than GLONASS compatibility. I don't know if the 66i is GLONASS-capable or not. I have looked more than once, and have not been able to identify the chipset used in the 66i.

Per customer support it is not supported. That said the 66st is advertised on several sites as supporting GLONASS.

I'm unclear on the response from support. Not supported on the 66st, or not supported on the 66i, or not supported on either? 

Although I would think it would be unusual, it's not out of the question that the two different 66 models use different chipsets. It's also possible that they are telling you what the current f/w release can do, not what the hardware is capable of. Which was your original question (and the more interesting question).

Not supported on the 66i.

I was out with my 66i this morning and it showed reception from 12 satellites, GPS I assume, what was I missing from not having a GLONASS as the 13th?  1/32" of accuracy?

I talked with support about this issue just after purchasing, after it was released.  I thought I'd gotten a very honest answer when they indicated that the 66i does support the Glonass Constellation, but, enabling this interferes with the Iridium Satellite capabilities in this device.  In other words, it can be turned on in firmware but the emergency capabilities may be compromised, and not be releable!  I have been carrying a 66ST and an InReach Explorer Plus, and only wanted to carry one GPS for all my needs.  Unfortunately, the 66i fails to let me do this since Glonass doesn't work.  I returned the 66i and will wait to see if they ever get this right!.  My tests indicated that the accuracy of the 66i wasn't any better than the GPS in the InReach (which has no Glonass) and it was just as bad, and not worth it, for me.  I'm still using the 66ST and an InReach Explorer Plus.

Old thread but the GLONASS frequency is very close to the iridium frequency. There isn't a steep enough filter to go in front of the GPS chip that will block the iridium transmissions but still allow GLONASS to come in.

The iridium transmit power could overload the RF front end of the GPS transceiver and burn out things like the LNA so I would think that to be safe they have a saw filter in front that blocks GLONASS and Iridium from the GPS chip. I would not expect to see GLONASS support on an iridium device for some time unless the antennas can have sufficient isolation or a new very steep saw filter comes out.

That seems to be a reasonable explanation, and would certainly account for the issue and no resolution.  I have long since repurchased the InReach explorer and moved on.  My main gripe is that Garmin touts this as the high end of the 66 series lineup,  and then basically cripples the GPS accuracy in communicator mode, with no mention anywhere.   Only comparing my track to a 66st and other devices indicated a real tracking issue.   I had to first purchase the product to find out it had this serious limitation, just before leaving on the PCT!  I had also sold my previous InReach explorer to purchase the 66i, so lost time and money there.  I, personally, am willing to pay a premium to eliminate carrying two devices, and this appeared to be their solution.  The technical issue of similar frequencies is solvable, but something obviously didn't work out or it would have been a simple firmware upgrade?  I'm hoping Garmin will have a solution in a future product generation, but won't hold my breath.  They have no competition and no incentive, which is a loss for everyone.

There are work arounds that could have be done, we did come up with a solution that allows both iridium and GLONASS on one of our devices with an iridium core module but a simple saw filter blocking it is easiest and it seems they went that route. No firmware update will ever fix it with a hardware filter blocking the frequency. If the filter wasn't there it would work right now as just about every GPS chipset works with GLONASS.

I still carry an old SPOT and a 62s. I want to replace both with an inreach but the lack of replaceable batteries holds me back. I don't want to deal with a bad internal LI-On in a couple years and on long trips I prefer to swap lithium AA/A's then carry power banks to recharge it. That was something that I expected Garmin to do right away when they took over the brand.