First of all, thanks for DT3, great job! I bought the upgrade immediately.
In DT2 you can use the Things3 quick entry hotkey (assuming you’ve set up the Things helper app) to automatically create a task in Things with a link back to the item in DEVONthink. This ist not working in DT3 beta1. Please fix this, DT and Things are the main apps in my workflow. THANKS!
Welcome @Saltex
Thanks for the nice feedback.
Note: We have no control over the behavior of Things. Also, we don’t run all the apps people run so it’s unclear what Things helper app you’re referring to. Please advise.
PS: DEVONthink 3 is in beta testing, meant for testing, finding and reporting bugs. It should not be used in mission-critical or production environments. Also, we advocate running it on a separate macOS user account with test data or copies of data.
The “Things helper app” is integrated in the task manager “Things 3” from Cultured Code and enables the quick creation of tasks by shortcuts. Things doesn’t support attachments, so many people use DEVONthink as file system. This works wonderful with DT2, but in tasks created in DT3 the important automatically inserted link back to DT (x-devonthink-item://…) is missing. But maybe the problem is on the side of Cultured Code an Things 3.
And it’s clear to me, DT3 is in beta status. 
Wrks fine EXCEPT that Things doesn’t pick up the LINK file from DevonThink3.
In DevonThink2 did it auto picked up the Link file? If so it might be Things issue.
Yes, in tasks Things3 created in DT2 the new tasks automatically picked up the link (x-devonthink-item://…). Not so in DT3 at the moment.
Email or tweet at Things see what they say
I have send an email to Cultured Code / Things. Lets see what they answer.
Blockquote
Liebes Team von Cultered Code! In DEVONthink2 kann man mittels “Kurzbefehl für Schnelleingabe mit Auto-Ausfüllen” einen Things-Task erstellen, welcher automatisch einen Link auf das Dokument in DEVONthink (x-devonthink-item://…) einfügt. Das funktioniert leider im neu erschienenen DEVONthink3 nicht - denn der Link wird nicht eingefügt! Wird das gefixt, denn viele User nutzen DEVONthink als Filemanager für Things … DANKE im Voraus für die Antwort.
In the meantime, the script in the script menu works well.
Thanks for the hint. Unfortunately, you can not enter tags, start date and group or project with the script. You have to open each task again in Things3 to make these settings. If you use DT3/Things3 very, very often each day, it is not practical.
The answer from Cultered Code:
Hallo Stefan,
DEVONthink hat intern einige Dateinamen geändert. Wir werden darauf in unserem nächsten Update reagieren.
Mit freundlichen Grüßen
Julia
Support @ Things
This means that they know the problem (DEVONthink has changed a few file names) and will react to it in the next update. 
The only things which are really different now are the bundle identifier and the app name but definitely not “internal filenames” (which shouldn’t even be used as they can change anytime).
I trust that the teams of DEVONthink3 and Things3 know about the problem of the many, many users which work with the combination DEVONthink3/Things3 and solve this issue.
DEVONthink beta4 is released now and Cultured Code still has not been able to make Things3 compatible with DEVONthink3. Very sobering … 
I really doubt they will do anything until DT is out of beta and is therefore stable.
This still isn’t working for me, is it for anyone? Things 3 used to pick up the DEVONthink item link when using the clipping shortcut, this was very useful in DT2. I’d like this to work in DT3 as well.
What’s the “clipping shortcut”?
When I use the script in DT3, I get an entry in Things3 that looks like this:
What I don’t like is Things3 will only create a deadline and not a due date with a reminder time.
Things has it’s own shortcut for clipping items, they call it Quick Entry with Autofill. See Things Preferences>Quick Entry. It takes information contextually and autofills it into the task. In DT2 it would automatically grab the DT item link, in DT3 it does not. I like using this shortcut instead of the DT script because I use it for getting other info into Things as well, like from Safari, so it’s just one shortcut to remember for clipping into Things.
Ah, okay, I was looking at it the other way; trying to figure out what the DT3 clipping shortcut was.
In case anyone is wondering: right now quick entry seems to be working without any issue with both apps up-to-date.
This post was one of the first results on Google when I searched to see how I can make Things and DT3 work together and since there was no update here I wanted to help other people like me who might find this thread in the future.