Can I connect sonos arc ultra to play:1

No, the Play:1s are not compatible surrounds with Arc Ultra.

Which Sonos speakers work as surrounds with Arc Ultra?

A matching pair of the following speakers will work as surrounds: Era 300, Era 100, Sonos One (including SL), Sonos Five, and SYMFONISK (Gen 2) speakers. You can also use Amp to power in-wall, in-ceiling, or other passive speakers as surrounds.

ok, so my next follow up question is - I also have a Sonos sub: Gen 3. The Arc Ultra will be connected to this sub. So will the sub act as a passthrough and help in connecting the play:1 as surrounds to the whole setup?

No, you cannot use the Play:1s as surrounds with Arc Ultra.

The Play:1s will still work as a stereo pair in a separate room or in individual rooms in the app.

It is so darn confusing!! The app has now discovered the play:1s and is allowing me to add it as surround. It asked for an update and that seems to somehow unlock it.

Are they possibly Ones rather than Play:1s?

I am 100% sure they are play:1s. The control buttons are located at the edge and not in the center. See the screenshot from my sonos app below -

Im interested…

so the Play 1s are compatible with the Arc Ultra or not?

Well the OP seems to have managed to add them given their screenshot above, but I would expect a future update to stop them being added as surrounds.

If the Play 1 have actually been added as surrounds for the Arc Ultra as OP screen shot to us,  I most admit and openly protest the gross injustice of having a future upgrade (ie firmware reconfigure) eliminate the hardware’s capacity to communicate and link up.  Especially since I forked over nearly 2 grand in cash to buy a sub 4 and arc ultra and what I’m seeing is it is possible for the devices to communicate and engage and that they would do something to a loyal consumer base as odious as prevent those loyal customers from using the devices they paid for in a desired way that would be possible were it not for that company purposely recoding the device’s communication protocol to force audio components into retirement.  If they can undo the ability for two devices to link up then they can REDO that ability.  I’m not above returning this arc ultra and sub 4 for a refund on the principal of forcing customers into purchasing new components for their audio system when their old components are so gently used they’re nearly new.  Customers who spread their personal appreciation for a product only to have the company crap on that loyalty by extracting money from them in rather unscrupulous business practices.  What say you Sonos?