`PYTHON_3_14` runtime accepted by CLI but rejected by CloudFormation

[azngeek]

Description

Description

The agentcore CLI (v0.9.1) allows PYTHON_3_14 as a valid runtimeVersion in agentcore.json and passes local validation (agentcore validate), but CloudFormation rejects the value during deployment with an AWS::EarlyValidation::PropertyValidation error. The resulting Change Set is created with status FAILED / ExecutionStatus: UNAVAILABLE, leaving the stack permanently stuck in REVIEW_IN_PROGRESS. No further deployments are possible without manually deleting the stack.

Expected Behavior

• Either PYTHON_3_14 should be accepted by CloudFormation (if the runtime is supported), or
• The CLI should not offer / validate PYTHON_3_14 until it is supported server-side, or
• At minimum, agentcore deploy should surface the CloudFormation validation error clearly and clean up the broken stack automatically.

Actual Behavior

1. agentcore validate succeeds with runtimeVersion: "PYTHON_3_14".
2. agentcore deploy creates a CloudFormation Change Set that immediately fails.
3. The stack is left in REVIEW_IN_PROGRESS — all subsequent deploys fail with:

   Stack "AgentCore-MyAgent-default" is currently in REVIEW_IN_PROGRESS state. Please wait for the operation to complete before deploying.

4. Manual intervention (stack deletion) is required to recover.

Steps to Reproduce

Steps to Reproduce

1. Create a new AgentCore project:

   agentcore init MyAgent

2. Add an agent with PYTHON_3_14 runtime:

   agentcore add agent
   # Select: Strands framework, PYTHON_3_14 runtime, CodeZip build

3. Verify agentcore.json contains:

   {
     "runtimes": [
       {
         "name": "MyAgent",
         "runtimeVersion": "PYTHON_3_14",
         "build": "CodeZip",
         ...
       }
     ]
   }

4. Run local validation (passes without error):

   agentcore validate

5. Deploy:

   agentcore deploy

6. Result: Change Set fails with:

   The following hook(s)/validation failed: [AWS::EarlyValidation::PropertyValidation]
   

7. All subsequent agentcore deploy calls fail because the stack is stuck in REVIEW_IN_PROGRESS.

Expected Behavior

Python 3.14 should be accepted.

Actual Behavior

Python 3.14 should be supported or at least more expressive error messages

CLI Version

0.9.1

Operating System

macOS

Additional Context

Component	Version
agentcore CLI	0.9.1
Node.js	v25.6.1
Python	3.14.3
OS	macOS (ARM64)
AWS Region	eu-central-1
CDK Bootstrap	v31

[jesseturner21]

Thank you for submitting this issue. For the time being you can change the version to PYTHON_3_13 or change the region to us-west-2 or us-east-1 as those have been tested.