A friend of mine whom I rely upon took it upon himself to put my question to a reliable contact of his. In the hope of adding some value to this thread, I'm reproducing this exchange with their names removed, in descending chronological order (latest first, earliest last).
Academic in the US:It’s almost all packet over OTN. SONET has been on its way out (at least in what I’ve seen) since the mid 2000’s. The last SONET I touched was like 2008, and that was to tear it out and replace it with Ethernet over OTN.
My contact: What you’re seeing pretty much matches what I’m seeing (from the outside). What I think Etienne is wondering is “how is that magic sauce delivered inside the SP network” - are they still using SONET/SDH, did they move to OTN, or is it pure packet-switched technology. The few networks I saw from the inside recently were all using packet-based technology (mostly MPLS) over lambdas. Would you have more data points?
Academic in the US: Almost everything I have seen in the US and parts of western Europe are either spectrum sharing (rare, but definitely a thing), wavelength as a managed service, or - more commonly - "managed ethernet" where the product is basically a L2 managed path with a hard bandwidth cap. This is far more common, especially in metro areas as it's basically part of pretty much all of the MetroE platforms. In the US, MPLS is still pretty heavy but MPLS-SR is likely going to take over that space. Carriers are selling waves at a premium, they'd much rather oversell a frame service.