Xcode Crashes During Code Completion with “EXC_BAD_ACCESS (SIGBUS)” on macOS 27.2 Beta

If Xcode quits as soon as you type in the source editor on macOS 27.2 beta, the crash may be caused by a known issue in enhanced code-completion ranking. The most useful signatures are EXC_BAD_ACCESS (SIGBUS) and MLSymbolPopularity.workQueue in the crash report. Apple has acknowledged the issue and recommends disabling enhanced code-completion ranking as a workaround.

Representative crash log
Cause
Affected conditions and versions
Recommended workaround
How to verify the workaround
Alternatives
How to restore the default setting
Important cautions
Summary
Official references

Representative crash log

Exception Type: EXC_BAD_ACCESS (SIGBUS)

Crashed Thread:
MLSymbolPopularity.workQueue

Espresso::inner_product_kernel_cpu::get_biases()
CodeCompletionModel.init
MLSymbolPopularity.loadModelIfNeeded

A typical case is that building, running, and debugging still work, but Xcode itself terminates immediately after you begin typing a new variable or identifier in the editor.

Cause

In the report discussed on Apple Developer Forums, the Core ML/Espresso path crashes while loading the predictive code-completion model. An Apple Product Manager confirmed that this is a known issue documented in the Xcode release notes.

This points to enhanced code-completion ranking on macOS 27.2 beta rather than an error in the app, code signing, DerivedData, or the Simulator. Cleaning the project therefore may not prevent the crash.

Affected conditions and versions

Apple’s documented scope: using Xcode code completion on macOS 27.2 beta
Forum reproduction: Xcode 27.0 (27A266a), macOS 27.2 beta 1 (26B5086k), and an Apple silicon Mac
The reported crash occurs on a keystroke in the source editor while builds, runs, and debugging remain functional

Fix status:As of September 30, 2026, Apple has not identified a fixed Xcode or macOS version. The Xcode 27.2 beta release notes list the behavior as a known issue and provide a workaround.

Recommended workaround

1. Quit Xcode

Save your work and quit Xcode completely so the preference change is picked up on the next launch.

2. Disable enhanced code-completion ranking

Run Apple’s documented workaround in Terminal:

defaults write com.apple.dt.Xcode CodeCompletionAssetsToLoad /dev/null

3. Relaunch Xcode and repeat the triggering edit

Open the same project and source location, then repeat the keystroke that previously caused the crash. This preference disables enhanced completion ranking; it does not necessarily remove every form of code completion from Xcode.

How to verify the workaround

Read the preference from Terminal:

defaults read com.apple.dt.Xcode CodeCompletionAssetsToLoad

The command should print /dev/null. Then confirm that Xcode remains open while typing and that no new crash report with MLSymbolPopularity is generated.

Alternatives

For production work, avoid macOS 27.2 beta and use a validated stable macOS/Xcode combination.
Apply the preference separately on each affected development or CI Mac until Apple publishes a fix.
If Xcode still crashes after applying the workaround, attach the crash report and a sysdiagnose to a Feedback Assistant report.

The original report states that deleting DerivedData and caches, reinstalling the completion model, changing “Display code predictions” to Never, and making inline completion manual did not resolve this particular crash. Those steps should not be presented as confirmed fixes for this issue.

How to restore the default setting

After Apple ships a confirmed fix, quit Xcode and remove the override:

defaults delete com.apple.dt.Xcode CodeCompletionAssetsToLoad

Relaunch Xcode and verify both completion behavior and editor stability.

Important cautions

EXC_BAD_ACCESS is a broad crash category. If the stack does not contain MLSymbolPopularity.workQueue or CodeCompletionModel.init, investigate other causes such as an app memory-access bug.
This workaround targets Xcode’s editor crash on macOS 27.2 beta. It does not fix an EXC_BAD_ACCESS raised by your running app.
No fixed version has been announced. Check current Xcode and macOS release notes before removing the preference.

Summary

When Xcode crashes on a keystroke with EXC_BAD_ACCESS (SIGBUS) and MLSymbolPopularity in the stack on macOS 27.2 beta, suspect the known enhanced code-completion ranking issue. Apply Apple’s CodeCompletionAssetsToLoad /dev/null workaround and verify that the same edit no longer terminates Xcode. Until a fixed version is officially documented, use the workaround or a stable OS/toolchain combination.