diff --git a/package-lock.json b/package-lock.json
index 684c3751ae..3cd84e87a5 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,6 +1,6 @@
 {
   "name": "rxjs",
-  "version": "7.0.0-beta.3",
+  "version": "7.0.0-beta.4",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {
@@ -8185,9 +8185,9 @@
       }
     },
     "typescript": {
-      "version": "3.9.2",
-      "resolved": "https://registry.npmjs.org/typescript/-/typescript-3.9.2.tgz",
-      "integrity": "sha512-q2ktq4n/uLuNNShyayit+DTobV2ApPEo/6so68JaD5ojvc/6GClBipedB9zNWYxRSAlZXAe405Rlijzl6qDiSw==",
+      "version": "4.0.1-rc",
+      "resolved": "https://registry.npmjs.org/typescript/-/typescript-4.0.1-rc.tgz",
+      "integrity": "sha512-TCkspT3dSKOykbzS3/WSK7pqU2h1d/lEO6i45Afm5Y3XNAEAo8YXTG3kHOQk/wFq/5uPyO1+X8rb/Q+g7UsxJw==",
       "dev": true
     },
     "uglify-js": {
diff --git a/package.json b/package.json
index 4127ab9281..ec43086b75 100644
--- a/package.json
+++ b/package.json
@@ -148,7 +148,7 @@
     "tslint-no-toplevel-property-access": "0.0.2",
     "tslint-no-unused-expression-chai": "0.0.3",
     "typedoc": "^0.17.8",
-    "typescript": "~3.9.2",
+    "typescript": "~4.0.1-rc",
     "validate-commit-msg": "2.14.0",
     "webpack": "^4.31.0"
   },
diff --git a/spec-dtslint/types-spec.ts b/spec-dtslint/types-spec.ts
index 254be7abbc..ef7aab679c 100644
--- a/spec-dtslint/types-spec.ts
+++ b/spec-dtslint/types-spec.ts
@@ -1,87 +1,87 @@
-import {
-  Observable,
-  ObservedValueOf,
-  ObservedValueUnionFromArray,
-  ObservedValueTupleFromArray,
-  Cons,
-  Head,
-  Tail
-} from 'rxjs';
-import { A, B, C } from './helpers';
-
-describe('ObservedValueOf', () => {
-  it('should infer from an observable', () => {
-    let explicit: ObservedValueOf<Observable<A>>;
-    let inferred = explicit!; // $ExpectType A
-  });
-
-  it('should infer from an array', () => {
-    let explicit: ObservedValueOf<A[]>;
-    let inferred = explicit!; // $ExpectType A
-  });
-
-  it('should infer from a promise', () => {
-    let explicit: ObservedValueOf<Promise<A>>;
-    let inferred = explicit!; // $ExpectType A
-  });
-});
-
-describe('ObservedUnionFromArray', () => {
-  it('should infer from an array of observables', () => {
-    let explicit: ObservedValueUnionFromArray<[Observable<A>, Observable<B>]>;
-    let inferred = explicit!; // $ExpectType A | B
-  });
-
-  it('should infer from an array of arrays', () => {
-    let explicit: ObservedValueUnionFromArray<[A[], B[]]>;
-    let inferred = explicit!; // $ExpectType A | B
-  });
-
-  it('should infer from an array of promises', () => {
-    let explicit: ObservedValueUnionFromArray<[Promise<A>, Promise<B>]>;
-    let inferred = explicit!; // $ExpectType A | B
-  });
-});
-
-describe('ObservedTupleFromArray', () => {
-  it('should infer from an array of observables', () => {
-    let explicit: ObservedValueTupleFromArray<[Observable<A>, Observable<B>]>;
-    let inferred = explicit!; // $ExpectType [A, B]
-  });
-
-  it('should infer from an array of arrays', () => {
-    let explicit: ObservedValueTupleFromArray<[A[], B[]]>;
-    let inferred = explicit!; // $ExpectType [A, B]
-  });
-
-  it('should infer from an array of promises', () => {
-    let explicit: ObservedValueTupleFromArray<[Promise<A>, Promise<B>]>;
-    let inferred = explicit!; // $ExpectType [A, B]
-  });
-});
-
-describe('Cons', () => {
-  it('should construct a tuple with the specified type at the head', () => {
-    let explicit: Cons<A, [B, C]>;
-    let inferred = explicit!; // $ExpectType [A, B, C]
-  });
-
-  it('should support rest tuples', () => {
-    let explicit: Cons<A, B[]>;
-    let inferred = explicit!; // $ExpectType [A, ...B[]]
-  });
-});
-
-describe('Head', () => {
-  it('should return the head of a tuple', () => {
-    let explicit: Head<[A, B, C]>;
-    let inferred = explicit!; // $ExpectType A
-  });
-});
-
-describe('Tail', () => {
-  it('should return the tail of a tuple', () => {
-    let explicit: Tail<[A, B, C]>;
-    let inferred = explicit!; // $ExpectType [B, C]
-  });
+import {
+  Observable,
+  ObservedValueOf,
+  ObservedValueUnionFromArray,
+  ObservedValueTupleFromArray,
+  Cons,
+  Head,
+  Tail
+} from 'rxjs';
+import { A, B, C } from './helpers';
+
+describe('ObservedValueOf', () => {
+  it('should infer from an observable', () => {
+    let explicit: ObservedValueOf<Observable<A>>;
+    let inferred = explicit!; // $ExpectType A
+  });
+
+  it('should infer from an array', () => {
+    let explicit: ObservedValueOf<A[]>;
+    let inferred = explicit!; // $ExpectType A
+  });
+
+  it('should infer from a promise', () => {
+    let explicit: ObservedValueOf<Promise<A>>;
+    let inferred = explicit!; // $ExpectType A
+  });
+});
+
+describe('ObservedUnionFromArray', () => {
+  it('should infer from an array of observables', () => {
+    let explicit: ObservedValueUnionFromArray<[Observable<A>, Observable<B>]>;
+    let inferred = explicit!; // $ExpectType A | B
+  });
+
+  it('should infer from an array of arrays', () => {
+    let explicit: ObservedValueUnionFromArray<[A[], B[]]>;
+    let inferred = explicit!; // $ExpectType A | B
+  });
+
+  it('should infer from an array of promises', () => {
+    let explicit: ObservedValueUnionFromArray<[Promise<A>, Promise<B>]>;
+    let inferred = explicit!; // $ExpectType A | B
+  });
+});
+
+describe('ObservedTupleFromArray', () => {
+  it('should infer from an array of observables', () => {
+    let explicit: ObservedValueTupleFromArray<[Observable<A>, Observable<B>]>;
+    let inferred = explicit!; // $ExpectType [A, B]
+  });
+
+  it('should infer from an array of arrays', () => {
+    let explicit: ObservedValueTupleFromArray<[A[], B[]]>;
+    let inferred = explicit!; // $ExpectType [A, B]
+  });
+
+  it('should infer from an array of promises', () => {
+    let explicit: ObservedValueTupleFromArray<[Promise<A>, Promise<B>]>;
+    let inferred = explicit!; // $ExpectType [A, B]
+  });
+});
+
+describe('Cons', () => {
+  it('should construct a tuple with the specified type at the head', () => {
+    let explicit: Cons<A, [B, C]>;
+    let inferred = explicit!; // $ExpectType [A, B, C]
+  });
+
+  it('should support rest tuples', () => {
+    let explicit: Cons<A, B[]>;
+    let inferred = explicit!; // $ExpectType [arg: A, ...rest: B[]]
+  });
+});
+
+describe('Head', () => {
+  it('should return the head of a tuple', () => {
+    let explicit: Head<[A, B, C]>;
+    let inferred = explicit!; // $ExpectType A
+  });
+});
+
+describe('Tail', () => {
+  it('should return the tail of a tuple', () => {
+    let explicit: Tail<[A, B, C]>;
+    let inferred = explicit!; // $ExpectType [B, C]
+  });
 });
\ No newline at end of file