I have Lutron Caseta at home and am getting close to my 50 device limit. Is it true that Hubitat can communicate with more than one hub and have say, picos on one hub control lights on the other hub?
If so, is there a maximum number of hubs that can be added to Hubitat?
Yes, Hubitat supports multiple Lutron Smart Bridge Pro devices (note that you do need the Pro bridge; Hubitat communicates via telnet over your LAN, and the non-Pro bridge does not support this). I'm not sure there's a hard limit on how many of those you can add, but I'd guess you'd start to question your life choices long before you add enough to Hubitat to notice any problems.
And yes, Hubitat can (for example) use a Pico from one Lutron bridge to control a light/switch on another Lutron bridge. Hubitat is the link here, since the automation (e.g., "when this Pico button is pressd, turn on this light") is set up in "Hubitat world", not "Lutron world," and Hubitat is able to communicate with both Lutron bridges. This should make sense if you think about it that way: the Hubitat integration will add the Lutron devices to Hubitat, so you can use Hubitat automations to control them (though in your specific example I'd say "must" rather than "can" since Lutron doesn't natively support what you want; otherwise there's no harm in leaving automations/etc. on Caséta as long as you don't mind keeping track of two different places where things could be happening).
Effectively no. You could add as many as you want. @bertabcd1234 gave a great description of what is possible and how it works.
Incidentally, if you create scenes for Caséta using the Luton mobile app, you can control those from Hubitat. To do so, you would add the bridge as a Lutron Keypad in the Lutron Integration, with id set to 1. Then, from the Integration Report you could see the "button numbers" assigned to each scene. "Pushing" one of those buttons from an app would cause that scene to activate.
I had no idea you could do that... I just modified my rule that shuts off all of my devices when I go to bed. Using the zigbee group messaging, and now this, this rule completes insanely fast compared to the 5-7 seconds when I first created it... Awesome!
You can probably find a used one on eBay or similar for less, but FYI, many people here (myself included) got their Pro bridge from Energy Avenue, which seems to have the cheapest prices--or did when I bought mine--for new.
Their Pico remotes are pretty reasonably priced, too (but you do have to pay shipping). I do have to confess that I don't actually have any hard-wired Caséta switches; I only got Caséta so I could use the Pico remotes as cheap, attractive, easily-mountable, familiar-to-guests button devices in Hubitat.
The one stumbling block I've run into with multiple Smart Bridge Pros is that the Lutron Caseta app only supports one Smart Bridge instance per account. I bought a second Smart Bridge Pro off of ebay for $40 and I don't currently have a pressing need to install it I haven't spent much time trying to get it setup. But I think you need to create a different user for the Caseta app, log in as that user, then setup the additional SB Pro in the Caseta app.
I'm sure someone will chime in if there's another way to do this.
I don't (yet) have two.. but I have been looking on Ebay occasionally...
I believe you're correct however... I remember reading that Hubitat does multiple, which isn't a feature from Lutron. But I could be remembering wrong.
Turns out I may not need multiple hubs after all. Lutron increased the Caseta device limit to 75. Might just be enough to cover those extra devices I've been postponing on connecting!