[ht85]

Here is a minimum "repro" of your use case:

tsconfig.json

    {
      "include": ["index.d.ts"],
      "compilerOptions": {
        "target": "es2015",
        "lib": ["es2015", "dom"],
        "moduleResolution": "node",
        "allowSyntheticDefaultImports": true
      }
    }

index.d.ts

    import * as PIXI from 'pixi.js'

    declare global {
      interface Window {
        PIXI: typeof PIXI
      }
    }

index.ts

    console.log(window.PIXI)

There is still an import but because it is in the .d.ts file it won't be included in the runtime code.

[umvi]

Thank you very much for posting this! I just tested this and it does exactly what I wanted - to get full type checking including 3rd party libs without having to convert all my existing files to be modules. I owe you a beverage of choice-