Understanding Edge Function CPU limits

Last edited: 2/6/2026

Learn how Edge Functions manage CPU resources and what happens when limits are reached.

How isolates work#

An isolate is like a worker that can handle multiple requests for a function. It works until a time limit of 400 seconds is reached. Edge Functions use isolates with soft and hard CPU limits.

Soft limit#

When the isolate hits the soft limit, it retires. This means:

It won't take on any new requests
It will finish processing requests it's already working on
It keeps going until it hits the hard limit for CPU time or reaches the 400-second time limit, whichever comes first

Hard limit#

If there are new requests after the soft limit is reached:

A new isolate is created to handle them
The original isolate continues until it hits the hard limit or the time limit
This ensures existing requests are completed while new ones are managed by a fresh isolate

Current limits#

Wall clock time limit: 400 seconds total duration
CPU execution time: 200 milliseconds of active computing

What happens when limits are exceeded#

When your function exceeds CPU limits, you may see:

546 error responses
Function termination with CPUTime shutdown reason
Degraded performance as new isolates spin up

Optimizing CPU usage#

Profile your code#

Identify CPU-intensive sections in your function:

Complex calculations
Data processing loops
Encryption operations

Optimize algorithms#

Use more efficient data structures
Cache computed results
Reduce algorithmic complexity

Offload heavy work#

Move intensive processing to background jobs
Use external services for heavy computations
Break large tasks into smaller functions