Listed spreads are native on CME, there are separate order books that have the same mechanics (order types, queue priority etc) as outright instruments. Same goes for the "relative products" such as BTIC, for example.Thanks, Some Lazy Element. One question that I've not been able to find an answer is how the "complex order book" of listed (i.e. native) futures roll calendar spreads works.
Some instruments have an implied spread order system that will match outright futures into a spread if the resulting market is tighter than current spread-book and display it there (I believe WTI is like that, but I might be wrong). It's not a custom combination of securities and, because listed spreads usually have smaller tick size, the added value of the implied spread orders is limited. CME also has a combo system and an RFQ system that allows you to combine multiple securities into a custom order, that's much more like COB on the option exchanges. You can see all that on platforms like CME direct.
It's worth learning more about these things for sure. Stuff like equity futures calendar spreads get a lot of liquidity when people are rolling and order books are quite thick. At other times, they could be pretty inefficient.