As per the folks at TTAC (researching CARB paperwork), there could be a 2019 model year for the Sonic after all.

The CARB document does not mention the 1.8L engine however, maybe Chevy is going to turbo all the trim levels?

https://www.arb.ca.gov/msprog/onroad/cert/pcldtmdv/2019/gm_pc_a0062154_1d4_u3-70.pdf