Salesforce Winter '27 Apex heap limits: 10 MB and 25 MB

Salesforce Winter '27 raises Apex heap limits from **6 MB to 10 MB for synchronous transactions** and from **12 MB to 25 MB for asynchronous transactions**. The increases activate automatically on the Winter '27 schedule.

Test against Summer '26 limits

When deploying from a Winter '27 sandbox to Summer '26 production, test against the target’s limits: **6 MB synchronous and 12 MB asynchronous**. A workload that fits within the higher sandbox limits can still exceed those production limits.

1. **Enable the compatibility setting.** In Apex Settings in the Winter '27 nonproduction org, enable **“Enforce the Summer '26 Apex heap limit”**. This setting exists only in Winter '27; Spring '27 enforces the higher limits globally.
2. **Verify both transaction contexts.** Use Limits.getLimitHeapSize() to confirm the active synchronous and asynchronous limits.
3. **Test affected workloads and record the evidence.** Identify the synchronous and asynchronous workloads affected by the change. Run them with the compatibility setting enabled and require them to pass under the Summer '26 limits. Attach the workload scope, active limits and test results to the deployment approval.

If a workload exceeds Summer '26 limits, the Apex developer should tell the business owner that the change is not ready for that production target. Hold deployment until it passes under those limits.

Treat these as heap-limit checks, not a general deployment-compatibility check.