Swift 6.4: What Actually Matters for iOS Developers

Swift 6.4 is here.

Released on September 15, 2026, Swift 6.4 brings improvements across the Swift language, standard library, tooling, Swift Package Manager, Foundation, and performance-focused APIs.

But if you’re an iOS developer, you probably don’t need a list of every feature in the release.

The more useful question is:

What does Swift 6.4 actually change for the way we build iOS and iPadOS apps?

The answer is mostly about less boilerplate, better concurrency diagnostics, easier migrations, better compiler behaviour, and improved tooling.

In this article, we’ll focus specifically on the Swift 6.4 changes that matter most to iOS developers.

1. async Is Now Allowed Inside defer

This is one of the most practical Swift 6.4 changes for concurrency-heavy applications.

Before Swift 6.4, this wasn’t allowed:

func performOperation() async throws {
    let resource = try await acquireResource()

    defer {
        await releaseResource(resource) // ❌
    }

    try await performWork()
}

This was inconvenient because defer is the natural place for cleanup, but cleanup…