az vm create --no-wait fails with "Extra data: line 1 column 4 (char 3)"

[Pepo48]

Describe the bug

Since yesterday (April 7, 2026), az vm create --no-wait fails with:

ERROR: Extra data: line 1 column 4 (char 3)

This is a JSON parsing error, most likely in the LRO continuation token handling introduced by the pickle-to-JSON migration in azure-core 1.38.0.

I can confirm that:

• Azure CLI 2.83.0+ (azure-core >=1.38.0) - fails
• Azure CLI 2.82.0 (azure-core 1.37.0) - works
  (tested in GH CI environment, on default Ubuntu runner)

The continuation token format was changed from pickle to JSON in azure-core 1.38.0 (Azure/azure-sdk-for-python#44574). A follow-up PR added azure-asyncoperation header handling in azure-mgmt-core (Azure/azure-sdk-for-python#44658).

Related command

az vm create --resource-group $RG --name $VM --nics $NIC --image Ubuntu2404 \
    --size Standard_D2s_v5 --admin-username azureuser --ssh-key-values key.pub \
    --authentication-type ssh --no-wait

Errors

ERROR: Extra data: line 1 column 4 (char 3)

Issue script & Debug output

Expected behavior

Command works.

Environment Summary

Additional context

The same CLI version (2.84.0, pre-installed on GitHub Actions runner image) worked on April 2 and broke on April 7, pointing to a server-side change exposing the bug.

Pinning azure-cli to 2.82.0 (last version using azure-core 1.37.0) helped as a workaround.

[yonzhan]

Thank you for opening this issue, we will look into it.

[rob-winkler]

I think this is related to the vm_image_alias_doc setting. It's currently set to https://azcliprod.blob.core.windows.net/cli/vm/aliases.json which 404s for me. A colleague has an older azure cli version which uses https://raw.githubusercontent.com/Azure/azure-rest-api-specs/main/arm-compute/quickstart-templates/aliases.json and that still works.

I set it to the old URL manually and it is a good workaround for now
az cloud update -n AzureCloud --endpoint-vm-image-alias-doc https://raw.githubusercontent.com/Azure/azure-rest-api-specs/main/arm-compute/quickstart-templates/aliases.json

[Travisivart]

Can confirm that this is due to the blob storage aliases.json missing https://azcliprod.blob.core.windows.net/cli/vm/aliases.json The above workaround also worked for us.

[Fastidious]

AZ cli (or the backend) is certainly broken. Is there an estimate time to fix for it?