Scaleway is part of the Iliad family of companies, which you probably haven't heard about if you're outside of Europe. This includes Online, a networking provider and Scaleway's parent, and Free, which is a huge French ISP with a fairly hackery internal culture.
Online makes their network map public:
Based on the names, it looks like it's 100% Cisco with a mix of Nexus 9000s, Catalyst 4500e edge, and 4900 ToR switches.
Scaleway is one of the only cloud providers I've seen that is using NBASE-T technology. The Intel Avoton SoCs used by their C2 instances support 2.5Gbps link speeds using an appropriate external PHY.
Their C1 instances are Marvell Armada 370 XP parts, datasheet here:
http://www.marvell.com/embedded-processors/armada-xp/assets/...
These are using 1 gig connections. The instances I've spun up connect to a gateway with a Cisco MAC address.
The C2 instances connect to gateways with MAC addresses registered to Freebox SAS. Figuring this out took some digging. It turns out that Scaleway/Online is manufacturing their own 2.5G capable switches. Because Free, the ISP, already has an OUI registered and was the only company in the conglomerate which made hardware, it looks like Online had Free make some custom switches to deploy in their datacenters.
They're also making their own BIOS for the C2 instances. dmidecode reports the following cutesy BIOS data:
Manufacturer: Online Labs Product Name: SR Version: (^_^) Serial Number: 42
The root devices for C1 and C2 instances are both NBD. Performance was better than I expected; I get wire rate I/O throughput on both (>90MB/sec on C1 and >250MB/sec on C2). Of course, the disk bandwidth is shared with the Internet connection on both instances, so there might be contention for some applications.