The role is new enough to be mistaken for jobs that overlap but aren't the same. The distinction is worth getting right, because it explains the compensation gap.
vs Solutions Engineer. An SE configures and integrates an existing product. An FDE builds new software in the client's environment when the product doesn't yet do what's needed. SE fits the product to the customer; FDE builds the missing piece, in production.
vs Sales Engineer. A sales engineer supports the deal — demos, POCs — and hands off after the sale. An FDE owns the post-sale outcome: the deployment that actually has to work. Pre-sale and persuasive versus post-sale and accountable.
vs ML / Research Engineer. They build the model. An FDE takes the frontier model as given and lands it inside a client's reality — pipelines, evals, legacy integration. The lab builds the engine; the FDE gets it driving on the client's roads.
The one-line test: a solutions engineer configures it, a sales engineer sells it, an ML engineer builds the model — a Forward Deployed Engineer makes it survive contact with the client's mess, and owns whether it works.