Note: This replaces three earlier changelogs that covered these changes separately. The breaking change date for all three is now July 17, 2026. Refer to this post going forward..
On July 17, 2026, CircleCI is shipping three changes to how configs are compiled. Pipelines affected by any of these changes will fail to compile after this date. Here are the 3 upcoming breaking changes:
- Undeclared parameters
Previously, referencing a parameter that is not declared in the current scope could silently resolve instead of raising an error, allowing invalid configs to compile.
After this date, configs that reference an undeclared parameter will fail to compile.
- Regex engine update for when: matches: conditions
The regex engine used to evaluate pattern: fields in pipeline configs is being updated to improve the security and reliability of config compilation. After this date, configs using any of the following regex features in pattern: fields will fail to compile:
- Negative lookaheads
- Negative lookbehinds
- Possessive quantifiers
- Backreferences
- version: 2.0 config support removed
Support for version: 2.0 configs is ending. All pipelines must use version: 2.1. Version 2.1 introduced orbs, pipeline parameters, reusable commands and executors, and a well-defined schema with strict validation.
For details on identifying impact and resolving any issues, see the Discuss post.