Announcement: sam deploy and sam sync now support CloudFormation Express mode

[roger-zhangg]

SAM CLI now supports CloudFormation Express mode

Starting with SAM CLI v1.163.0, sam deploy and sam sync support the new CloudFormation Express mode via the --express flag.

Default behavior

Currently, --express defaults to off for both sam deploy and sam sync to maintain backwards compatibility.

⚠️ Starting September 1, 2026, we will flip the default for sam sync to use express mode by default (--express on), since sync is designed for fast development iteration. You can opt out with --no-express. The sam deploy default will remain off.

What is Express mode?

Express mode completes stack operations up to 4x faster by returning once resource configuration is applied, without waiting for full stabilization (traffic readiness, edge propagation, resource cleanup). Resources continue becoming ready in the background.

How to use it

# Deploy with express mode
sam deploy --express --stack-name my-stack --resolve-s3 --capabilities CAPABILITY_IAM

# Sync with express mode
sam sync --express --stack-name my-dev-stack

# Persist in samconfig.toml
sam deploy --express --save-params

Behavior

• sam deploy --express: Passes DeploymentConfig={"Mode": "EXPRESS"} to CloudFormation's CreateChangeSet API
• sam sync --express: Passes DeploymentConfig={"Mode": "EXPRESS"} to CreateStack/UpdateStack APIs
• The --disable-rollback flag works with express mode (passed inside DeploymentConfig)
• After deployment, a message reminds users that resources may still be stabilizing in the background
• Persists to samconfig.toml via --save-params as express = true

Requirements

• SAM CLI >= 1.163.0
• No template changes required — works with all existing templates and nested stacks
• Available in all AWS regions where CloudFormation is supported

Links

• CloudFormation Express mode announcement
• PR #9106