Dash 4 RC, Loading indicator behavior + ag-grid upgrade question

Dash Python
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Hi Dash team,
We are currently doing a POC on Dash 4.0.0 RC and wanted to share some observations and get guidance before we move further

Loading icon behavior (main concern):

What we see right now:

  • dcc.Loading works fine when callbacks are triggered by user actions (Apply button, filter click, etc.)

  • On initial page load:
    Callbacks do execute (data loads correctly)
    But loading spinner is not shown
    User just sees blank graph / table for a few seconds

This was not the case in Dash 2.x. Earlier, users always saw a spinner during initial load.

What we did as a workaround: To avoid bad UX, we added a custom overlay spinner for initial page load and kept dcc.Loading for user-triggered actions.
This works functionally, but now:

  • We have two different loading icons
    One from dcc.Loading
    One custom overlay spinner
  • UI looks inconsistent
  • Extra state + extra code to maintain

**Our understanding of the issue: **
From what we observed:

  • In Dash 4, loading detection works differently

  • On initial load:
    Page renders
    Callback fires almost immediately
    dcc.Loading doesn’t reliably catch that execution

  • Result → no spinner, even though callback is running

Just want to confirm:
**Is this expected behavior in Dash 4 or a known issue?

**
Questions we need help with :

  1. Is the initial page load loading issue expected in Dash 4?

  2. Will this be fixed in Dash 4 GA?

  3. What is the recommended way to show loading indicators?

  4. Should teams rely on custom overlays or wait for a native fix?

  5. Apart from dash-ag-grid>=32.0.0, is there anything else we must upgrade?

  6. How long should we expect this behavior to remain?

Regards,
Munish Singla

2

Hi Munish, thanks for trying out the Dash 4 rc and for reporting this issue!

I’m having trouble reproducing the issue as described. On my end, I do see the Loading indicator during the initial page-load callback. I’m wondering if you can you provide some minimal code example that shows the problem?

Some specific answers to your questions:

  1. We intend for dcc.Loading (and all components) to be backwards-compatible, so a change in behaviour from Dash 3 is not expected.
  2. Yes, if we can get to the root cause
  3. The recommended ways to show loading indicators is described in our docs - these examples apply to Ag Grid too. As mentioned, I’d like to see a code example of what you were doing that previously worked but does not in v4.
  4. That will depend on your own priorities. We are doing release candidates to address precisely this kind of feedback ahead of the full release. So our intention is to fix bugs as they are found.
  5. No
  6. Not long once we confirm the bug.
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