31 October 2025, 00:29 UTC

We are issuing an urgent advisory regarding an incompatibility between Compute services and the newly released Rust version 1.91.

Action Required 

We strongly recommend that you DO NOT upgrade to Rust version 1.91 at this time.

What Happened

We first identified this incompatibility in our testing environment on the 30th of October 2025, and have since confirmed the same Compute crash behavior in our production environment.

• Incompatible Version: Rust 1.91

• Compatible Version: Rust 1.90 and below (Previous Stable Versions)

• Impact: Using Rust 1.91 with Compute may lead to crash behavior, which will impact your traffic on Fastly.

What’s next? What do I have to do?

If you have already upgraded your services to Rust version 1.91, you must immediately downgrade to the previous stable and compatible version, Rust version 1.90, to prevent or resolve any impact to your traffic.

We are actively working on a fix to ensure compatibility with Rust version 1.91 and will provide an update as soon as a fix is available. Thank you for your patience and understanding.

Customers with any questions or concerns may engage with our Support team through https://support.fastly.com or by contacting your designated account management team members.