According to sources cited by the Nikkei Asian Review, Google may be working on a 5G-capable Pixel 4. The handset may be announced at Google's Pixel event on October 15th but likely wouldn't be available for months. However, considering how new and small 5G networks are, a 5G-compatible Pixel 4 seems unlikely.
https://www.notebookcheck.net/Google-may-be-working-on-a-Pixel-4-with-5G.437699.0.html