Thanks for the details — this is a common gotcha on Windows/PowerShell. What’s happening - When you use PowerShell’s

>

redirection, it can write the file with an encoding (often UTF-16) that doesn’t parse cleanly when Prefect reads it as JSON, leading to

json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

. - It can also silently produce an empty file if something went wrong upstream, which triggers the same error. Two easy fixes 1) Generate the file using the built-in

--file

flag (recommended) This avoids shell redirection and writes the correct encoding.

prefect work-pool get-default-base-job-template --type kubernetes --file base-job-template.json
prefect work-pool update k8s-pool --base-job-template .\base-job-template.json

2) If you already have a file, re-save it as UTF-8 In PowerShell:

Get-Content .\base-job-template.json | Set-Content -Encoding utf8 .\base-job-template-utf8.json
prefect work-pool update k8s-pool --base-job-template .\base-job-template-utf8.json

Quick checks - Ensure the file isn’t empty:

Get-Content -Head 1 .\base-job-template.json

- You can validate it parses as JSON:

python -c "import json,sys; json.load(open('base-job-template.json', encoding='utf-8')); print('OK')"

If that still errors, please let me know: - Which shell/OS you’re using (PowerShell, CMD, Bash, etc.) - Whether

prefect work-pool get-default-base-job-template --type kubernetes

prints JSON directly in your terminal - The first few non-sensitive characters of the file (e.g., does it start with

{

) For reference, the CLI has a

--file

option specifically for this use case:

prefect work-pool get-default-base-job-template --help

Shows: -

--file  -f TEXT  If set, write the output to a file.

Once the file is UTF-8 JSON,

prefect work-pool update

should accept it without issue.

Short answer: No restart needed. In Prefect 3.x, workers fetch the base job template from the API at job submission time. After you update the work pool’s base-job-template, any new flow runs the worker picks up will use the updated template automatically. Already-running or already-submitted runs won’t be affected. You would only need to restart the worker if you changed something about how the worker process itself runs or authenticates (e.g., its environment variables, kubeconfig, or Python environment), since those are loaded when the worker starts. Quick sanity check:

prefect deployment run <FLOW_NAME>/<DEPLOYMENT_NAME> --watch

Then inspect the created Kubernetes Job to confirm it reflects your changes (image, env, resources, etc.). Background on the workers model in Prefect 3.x: Prefect 3 GA