What are the obligations of my current and new employers during my work permit transition in Thailand?

Pro advice here. This makes facebook groups good.

other than provide you the documents you need to cancel your current work permit and cancel your extension of stay your current company is under NO obligation to do anything at all.

AND conversely your new company isn't obligated to do more than give you the documentation to apply for a new work permit and new visa and or extension.

Now that they WILL help you is another issue entirely and needs to be addressed with both your current and new employer on how much or how little they will do for you.

just so we're clear it's YOUR work permit and the place you work for is just listed as an employer. YOU need to take ownership of what happens to it, NOT your soon to be former employer and your soon to be new employer because at the end of the day if things are done wrong it comes back on you not them.

In theory, it can go smooth, but for that your old company, new company, the Ministry of Labor and the Immigration Office have to work side by side and make all the transitions on time. This is Thailand, meaning in real life, you go to cancel with a letter of your old employer to the Ministry of Labor and cancel YOUR work permit, than with those documents you go, if you have the big stamp from Immigration in your passport, to Immigration Office to cancel this Extension of Stay and go abroad for a new visa. In the mean time your new employer can apply for a new Work Permit and sort out the documents for you to apply for a new Non Immigrant B visa.