Pulsating dot that indicates activity does not show up

[ssrmm]

Describe the bug
I'm in the process of updating some old code to the latest version of Chainlit. In the current version, the pulsating dot that indicates that content is being generated does not show up until at least on token has been streamed. This is a regression introduced in in 1.1.400, version 1.1.306 works as expected.

To Reproduce
In 1.1.306, below code would generate an empty response message and show a pulsating dot immediately:

import chainlit as cl

@cl.on_message
async def main(message: cl.Message):
    await cl.sleep(3)  # Simulate LLM call taking some time
    await cl.Message(f"You said: {message.content}").send()

Starting with 1.1.400 it doesn't anymore. Now this seems somewhat reasonable because it is faking a response where there is none yet. So I have tried this instead:

import chainlit as cl

@cl.on_message
async def main(message: cl.Message):
    response = cl.Message("")
    await response.send()
    await cl.sleep(3) # Simulate LLM call taking some time
    await response.stream_token(f"You said: {message.content}")
    await response.update()

I would expect at least this code to generate the pulsating dot in the response immediately, but it does not in versions later than 1.1.400. In 1.1.306 it does as expected.

Streaming an "invisible" token triggers the pulsating dot, but is really only a workaround that imho should not be necessary.

import chainlit as cl

@cl.on_message
async def main(message: cl.Message):
    response = cl.Message("")
    await response.send()
    await response.stream_token("\u00A0") # Zero-width non-breaking space to force the pulsating dot
    await cl.sleep(3) # Simulate LLM call taking some time
    await response.stream_token(f"You said: {message.content}")
    await response.update()

Expected behavior
A pulsating dot is shown to indicate to the user that a response is being generated and to avoid users thinking the application is broken because there is no feedback.

Screenshots
Chainlit 2.6.7, first code snipped:

Chainlit 2.6.7, second code snipped:

Chainlit 2.6.7, third code snipped. Note the gray dot next to the avatar, it would be pulsating if this was a video instead of a screenshot)

Chainlit 1.1.306, first code snippet. Note that this works exactly like the third code snipped in the latest version, but with less amount of code.

Desktop (please complete the following information):
Any browser, N/A

Smartphone (please complete the following information):
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Additional context
N/A

[dosubot]

You're right—this is a regression that started in Chainlit 1.1.400. The pulsating dot (loader) now only appears if the message content is empty, and it doesn't show up immediately when you send an empty message and wait before streaming tokens, unlike in 1.1.306. This change is tied to updates in how message and step rendering works, which also caused other UI differences in newer versions see discussion.

The best-known workaround is to stream an "invisible" token (like a non-breaking space) right after sending the empty message, which triggers the loader, but this is admittedly a hack. There isn't an official fix or recommended alternative as of now. For reference, a maintainer confirmed that the loader only works while the message content is empty see here.

If you want to ensure users see activity feedback, you'll need to keep using the invisible token trick until the loader logic is updated in a future release.

To reply, just mention @dosu.

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[ssrmm]

Oh yeah, I forgot to mention relevant, related issues:

• Progress bar / spinning wheel #588
• Why is the loading icon not showing? #1254
• Missing blinking dot #1354

However, none of them resolve this case. The second issue mentioned by the bot does not apply either, in this scenario the content is empty as suggested in that issue.

[dosubot]

You're right—issues #588, #1254, and #1354 are unrelated and don't address the loader regression. The root cause is a change in message and step rendering introduced in 1.1.400, which affects how the loader (pulsating dot) is triggered and displayed. The most relevant discussion is in issue #2365, where users confirm this regression and its impact on UI feedback. As of now, there’s no official fix or better workaround than the invisible token trick.

To reply, just mention @dosu.

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