Likely to cause new Flow errors:

• Improved generic type inference with conditional types. Some places might infer a different type and cause new errors.
• Number, String, RegExp, Date, native errors, maps, and sets now use TypeScript-style instance and constructor interfaces, while Math, JSON, and Atomics use named interfaces. Existing code relying on their previous class or object typing may produce new errors.

New Features:

• Allow object type spreads over interfaces and inexact object types.

Notable bug fixes:

• Allow classes to extend generic construct-signature interfaces.
• Generic values re-exported through annotated CommonJS getters retain their polymorphic types.
• Preserve record lowering source locations.
• Preserve match lowering source locations.

Parser:

• Support semicolonless abstract method declarations.