I have just ordered one of the new Nov 2018 MacBook Airs that only come with Thunderbolt 3 (USB-C) ports. Just looking for a simple clean solution for a high performance adapter using the USB-C physical connector.

Notes:

1. I am aware of the many USB-C to gigabit ethernet adapters that exist -- but I am looking for an adapter that takes advantage of Thunderbolt 3, the lower latency, and lower overheads. For example, on my old MacBook Air (2014), I use a Thunderbolt to Ethernet adapter ---> NOT a USB to Ethernet adapter.

2. I am aware I can buy a Thunderbolt 3 to Thunderbolt adapter, and then plug in my Thunderbolt to Ethernet adapter ... but I don't want a double dongle. Who does?

Does there exist a Thunderbolt 3 to Gigabit ethernet adapter?

(n.b. the rest of this should be made into an answer and edited out including this editor's note...)

Note on the USB-C to Ethernet that Apple sells (Belkin)

If you read the reviews on the USB-C to Ethernet adapter that Apple officially sells (made by Belkin), there are a number of reviews that suggest that speed is throttled by using the USB-C adapter (compared to Thunderbolt).

A review by Elias A states:

"Compared the old macbook dongel that has thunderbolt with this one. Got close to 1000Mbits. With this Belkin USB-C dongel I get around 200-300 Mbits"

A review by William S states:

Not really gigabit This adapter is only recognized as a 100BaseTX, even if you try to set it manually. Returned it and bought a Thunderbolt 3 (USB-C) to Thunderbolt 2 adapter since I already had an old Thunderbolt to Ethernet adapter from Apple. This combo may not be elegant, but it gives me full gigabit speed

It is these reviews that prompted my question. There are other reviews that note that Thunderbolt also involves lower system resources than USB-C.

Update after buying Belkin USB-C to gigabit Ethernet adaptor

Based on one of the answers below, I unfortunately purchased the Belkin USB-C to gigabit ethernet adaptor ... and report below some comparison timings which reflect very poorly on the product.

In the following tests, I compare the speed to transfer, on the same Cat6 ethernet network, over the same cables, through the same routers:

• 2014 Macbook Air: using Apple Thunderbolt to Ethernet adaptor
• 2018 Macbook Air Retina: using Belkin USB-C (plugged into Thunderbolt 3 port) to Ethernet adaptor

Test 1: 3.8GB file

• 2014 Mac - Apple Thunderbolt adaptor: 35 seconds
• 2018 Mac - Belkin USB-C: 110 seconds. (Repeat tests returned 35 secs)

Test 2: 9.6 GB folder (with many files)

• 2014 Mac - Apple Thunderbolt adaptor: 5 min 50 seconds
• 2018 Mac - Belkin USB-C: 6 min 45 seconds

Test 3: 4 GB movie

• 2014 Mac - Apple Thunderbolt adaptor: 63 seconds
• 2018 Mac - Belkin USB-C: 87 seconds

The Belkin adaptor also got very very hot, and smelled burnt. I cannot explain the wildly variable results from the Belkin product either. An adaptor that returns worse results on a much faster 2018 Macbook Air (using USB-C) than Apple's own Thunderbolt adaptor on the 2014 Macbook Air frankly beggars belief. Whether the fault is the Belkin unit (of which there are many complaints on the Apple store site) or some inferior aspect of using USB-C compared to Thunderbolt ... I cannot say.

I will be returning the Belkin unit to the Apple store for a full refund: the product or technology is plainly inferior to what was available 4 years ago.

The ridiculous answer to your question is: buy the Apple Thunderbolt 2 to Ethernet adapter AND the Apple Thunderbolt 2 to Thunderbolt 3 adapter and daisy chain them.

As far as I can tell, that is currently the only way to get your ethernet to show up as Thunderbolt on the newer MacBook Pros.

We use the Belkin USB-C on all our thunderbolt 3 Macs and get speeds far in excess of the review people. I would expect they either got a bad adapter (it happens - even the best hardware companies can't ship every product perfect - that's what warranty support and service are for - to fix that).

We've never had a case where we needed to get a more expensive 10 GB adapter in our experience. We also get 500 to 700 MBps from the MacBook which only does USB with the Belkin adapter.

I would get those until you have a specific case you can't fix with networking checks and quality switches rather than spend more on an exotic combination of 10 GB adapters that run $200+ from the good vendors:

• https://www.sonnetstore.com/collections/thunderbolt-10gbe-adapters/products/solo-10g
• https://www.sonnetstore.com/collections/thunderbolt-10gbe-adapters/products/twin-10g-thunderbolt3-edition

Sonnet's Thunderbolt 2 adapters do very well in our high bandwidth use cases - MacPro serving files or accessing a SAN as do their thunderbolt to SFP adapters. They are pro supported and designed gear for always on use. We rarely if ever need to put them in a design studio or for ProSumer use, but if you have the funds, these are fun adapters that really work well.

For 95% of our use cases - the Belkin is the adapter to choose.

The only Thunderbolt 3 Ethernet adapters I'm aware of are either part of TB3 docks or really bulky 10GigE Ethernet adapters. A USB-C GigE adapter will do just fine. I got one by Aukey for about 10€ which works pretty much just like the TB2 Ethernet adapter from Apple (it even looks the same). Same speed (100+ MB/sek realworld speed to my NAS), no latency or overhead issues.