How do I import Typescript types from an NPM package?

I'm using an NPM package Constate (https://github.com/diegohaz/constate). In node_modules/constate, it includes several type definition files:

constate/
  dist/
    ts/
      src/
        types.d.ts
  src/
    types.ts

And in Constate's package.json, it has:

"types": "dist/ts/src",

I'm trying to import a type from either types.ts or types.d.ts. I tried:

import { SplitValueFunction } from 'constate/dist/ts/src/types';
import { SplitValueFunction } from 'constate/dist/ts/src/types.d';
import { SplitValueFunction } from 'constate/dist/ts/src/types.d.ts';
import { SplitValueFunction } from 'constate/src/types';
import { SplitValueFunction } from 'constate';

None of these work. What's the proper convention to import types from an NPM module? What's the purpose of the types field in package.json?