Introduction

Historically, Xcode exposed both Architectures and Valid Architectures, and the names sounded similar enough to confuse almost everyone. The short version is that Architectures described what the target should build for, while Valid Architectures acted as a filter of what Xcode considered allowable on that toolchain and SDK; in modern Xcode, VALID_ARCHS is legacy and the effective result is usually driven by Architectures, platform settings, and excluded architectures instead.

What Architectures Meant

Architectures, often shown as ARCHS, tells Xcode which CPU architectures the target is supposed to compile for.

Examples from Apple platform development have included values such as:

• 'arm64 for device builds,'
• 'x86_64 for simulator builds on Intel Macs,'
• and older values such as armv7 in older iOS eras.

Conceptually, this setting answers the question:

"Which architectures do I want this target to build?"

If the target builds for more than one architecture, Xcode can produce a binary containing multiple slices when that is appropriate for the platform and build context.

What Valid Architectures Historically Meant

Valid Architectures, often shown as VALID_ARCHS, historically answered a different question:

"Which architectures are even considered valid choices in this environment?"

So the effective build architectures were historically constrained by the interaction between:

• the requested architectures,
• the valid architectures known to the SDK and toolchain,
• and the destination platform such as device or simulator.

That is why the two settings were related but not identical. One expressed intent, while the other imposed an allowed set.

Why This Became Confusing

In real projects, developers often edited both settings without a clear mental model. That led to a lot of problems such as:

• requesting an architecture that was filtered out elsewhere,
• carrying old architecture values forward long after the platform moved on,
• and trying to fix build issues by tweaking VALID_ARCHS when the real issue was a simulator-versus-device mismatch.

The confusion got worse as Apple platforms evolved and some older architecture values became irrelevant.

Modern Xcode Context

In modern Xcode versions, VALID_ARCHS is effectively a legacy setting and is no longer the normal knob to rely on. The practical decisions now are usually driven by:

• 'Architectures,'
• target platform and SDK,
• 'Excluded Architectures,'
• and the build destination such as simulator versus physical device.

That means if you are reading older advice that tells you to edit Valid Architectures, treat it cautiously. In current Xcode workflows, the more relevant question is usually which architectures are requested and which ones are excluded for a specific build context.

A Practical Example

Suppose you are building for an iPhone device. The important architecture today is typically arm64. If you are building for a simulator, the effective architecture may differ depending on whether the development machine is Intel-based or Apple silicon.

The modern debugging question is usually not "what is in VALID_ARCHS?" It is more often:

• what platform am I targeting,
• what architecture is being requested,
• and is something excluded that prevents the expected slice from building?

That shift is why old explanations based heavily on Valid Architectures are less useful in current Xcode projects.

Common Pitfalls

• Treating Architectures and Valid Architectures as interchangeable settings.
• Following old Xcode advice that assumes VALID_ARCHS is still a primary control in modern projects.
• Debugging simulator and device architecture mismatches without checking the actual build destination.
• Carrying obsolete architecture values forward from old project templates.
• Trying to fix build issues in the wrong setting when the real issue is platform, SDK, or exclusion logic.

Summary

• Historically, Architectures meant the architectures a target wanted to build for.
• 'Valid Architectures historically acted as a filter of which architectures were allowable in that environment.'
• The two settings interacted, but they were never the same concept.
• In modern Xcode, VALID_ARCHS is legacy, and current architecture behavior is usually understood through ARCHS, destination platform, and excluded architectures.
• When debugging build issues today, focus more on current platform and exclusion settings than on old Valid Architectures guidance.