Slack Block Kit Select Menus: Static, Multi, Users and External, Tested

A Block Kit select menu is an element you put in a section's accessory or an actions block. static_select takes up to 100 options you send with the message, multi_static_select lets people pick several, users_select lists the workspace's members, and external_select asks your app for options as the user types. On 3 October 2026 we posted all four from a Bolt for Python Socket Mode app in our own test workspace, picked a value in each, and timed the external options handler. The external menu has a hard 3 second limit, and missing it does not show an error.

The message we posted

def opt(t, v): return {"text": {"type": "plain_text", "text": t}, "value": v}
FRUIT = [opt("Apple", "apple"), opt("Banana", "banana"), opt("Cherry", "cherry")]

blocks = [
  {"type": "section", "block_id": "s_static", "text": {"type": "mrkdwn", "text": "*static_select*"},
   "accessory": {"type": "static_select", "action_id": "pick_static",
                 "placeholder": {"type": "plain_text", "text": "Pick a fruit"}, "options": FRUIT}},
  {"type": "section", "block_id": "s_multi", "text": {"type": "mrkdwn", "text": "*multi_static_select*"},
   "accessory": {"type": "multi_static_select", "action_id": "pick_multi",
                 "placeholder": {"type": "plain_text", "text": "Pick fruits"}, "options": FRUIT, "max_selected_items": 2}},
  {"type": "section", "block_id": "s_users", "text": {"type": "mrkdwn", "text": "*users_select*"},
   "accessory": {"type": "users_select", "action_id": "pick_user",
                 "placeholder": {"type": "plain_text", "text": "Pick a person"}}},
  {"type": "section", "block_id": "s_ext", "text": {"type": "mrkdwn", "text": "*external_select*"},
   "accessory": {"type": "external_select", "action_id": "pick_ext",
                 "placeholder": {"type": "plain_text", "text": "Search tickets"}, "min_query_length": 0}},
]
client.chat_postMessage(channel=channel_id, text="612 select menus", blocks=blocks)

One listener caught every pick:

@app.action(re.compile("pick_.*"))
def picked(ack, body):
    ack()
    print(json.dumps(body["actions"][0]))

The block_actions value for each menu

These are the actions[0] objects Slack sent when we picked a value:

{"type": "static_select", "action_id": "pick_static", "block_id": "s_static", "selected_option": {"text": {"type": "plain_text", "text": "Banana", "emoji": true}, "value": "banana"}, "placeholder": {"type": "plain_text", "text": "Pick a fruit", "emoji": true}, "action_ts": "1790989996.318666"}
{"type": "multi_static_select", "action_id": "pick_multi", "block_id": "s_multi", "selected_options": [{"text": {"type": "plain_text", "text": "Apple", "emoji": true}, "value": "apple"}, {"text": {"type": "plain_text", "text": "Banana", "emoji": true}, "value": "banana"}], "placeholder": {"type": "plain_text", "text": "Pick fruits", "emoji": true}, "action_ts": "1790990058.398004"}
{"type": "users_select", "action_id": "pick_user", "block_id": "s_users", "selected_user": "U0B7L4YK420", "action_ts": "1790990079.293592"}
{"type": "external_select", "action_id": "pick_ext", "block_id": "s_ext", "selected_option": {"text": {"type": "plain_text", "text": "all result 1", "emoji": true}, "value": "all-1"}, "placeholder": {"type": "plain_text", "text": "Search tickets", "emoji": true}, "action_ts": "1790990342.110390"}

Read selected_option.value for single selects, selected_options[].value for multi selects, and selected_user for users_select. The full envelope around these objects is on our interactivity payload page.

Things we saw that the reference does not mention:

• • users_select listed bots and deactivated apps too: our test app, Slackbot, Slack Security, and four deleted test apps marked "(deactivated) APP". Check selected_user with users.info if you only want people.
• • In a message, multi_static_select does not open a dropdown. It opens a "Pick fruits" dialog with the line "You can select up to 2 items." and Cancel and Confirm buttons. The pick is sent only on Confirm.
• • Picking a third item turned the hint into a warning and disabled Confirm:

When we closed that dialog with Escape, no event reached the app, yet the button in the message read "3 selected" until we reopened it. Do not trust what the button says; trust the last block_actions you received.

How long the external options handler can take

The handler slept for a set time, then answered with options named after the query, so we could tell old results from new ones:

@app.options("pick_ext")
def ext_options(ack, body):
    time.sleep(DELAY)
    q = body.get("value") or "all"
    ack(options=[opt(f"{q} result {i}", f"{q}-{i}") for i in range(1, 6)])

We typed a new query each time and recorded the menu's text every 50 ms in the browser. Slack showed "Loading results…" under the old list at once. Times are from the last keystroke:

Even a 0-second handler took about a second to show, because Slack waits for typing to pause before it asks your app. Past 3 seconds there was no error, no "No results", nothing. The menu dropped the spinner and kept the previous query's results under the new query:

That is worse than an error, because a user can pick a result that does not match what they typed. Bolt for Python also gives up at 3 seconds and logs Unhandled request ({'type': 'block_suggestion', ...}). To rule out Bolt, we answered the same requests from a bare slack_sdk SocketModeClient with no timeout of its own. Answers at 2.9 s showed up; answers at 3.5 s and 5 s were ignored the same way. The 3 second limit is Slack's.

So keep the options handler under about 2.5 seconds: query an index or a cache, never a slow API, and return fewer, better matches.

Limits Slack enforced

So option text tops out at 75 characters and values at 150. The silent failure for 101 external options matches the timeout case: if your search can return more, cut the list to 100 before you ack.

To build these blocks by hand first, our Block Kit Builder guide shows the preview workflow, and the invalid_blocks guide explains how to read the json-pointer in each error.