What does a Forward Deployment Engineer actually do day to day, and how is that different from a typical backend or DevOps engineer?

A backend engineer mostly builds generic, reusable features for many customers behind a stable internal environment. A DevOps/SRE engineer mostly operates and hardens infrastructure the team already controls. An FDE does neither in isolation: they sit with (or close to) one customer, learn their actual business process and data, and write integration code, pipelines, or UI configuration that makes the core product work inside that customer's environment — which is often locked down, inconsistent, and outside the company's control.

Day to day this looks like: reverse-engineering undocumented customer APIs or database schemas, writing ETL/integration code against messy real-world data, debugging inside customer-controlled networks (VPNs, firewalls, on-prem clusters, air-gapped environments), and iterating quickly with the customer in the room rather than through a ticket queue. The FDE is also expected to feed generalizable gaps back to the core product team instead of only patching around them locally.