Although Google's most recent post indicates that they're "working with other partners to offer connected experiences that deliver more custom integrations," developers still haven't received any details. The Nest developer forum is still locked down and there's no way to contact Nest's developer support.
I will continue to operate ThermoTweak as long as I can, and will convert to Works with Google Assistant if/when the functionality required by ThermoTweak is supported. In the meantime, though, users may want to consider canceling annual subscriptions (to prevent them from autorenewing) if they are concerned about ThermoTweak no longer functioning in the future.
It appears that Google is adjusting their approach.
For now, as long as you do not convert your Nest account to a Google account, ThermoTweak will continue to work.
As more information is released regarding custom integrations like ThermoTweak, I'll have a better sense of whether or not ThermoTweak will be able to continue to operate long-term. In the meantime, all subscription plans will remain in effect.
On May 7, 2019, Google announced that Nest is becoming Google Nest, and Google is canceling the Works with Nest program.
According to Google, "Third parties will no longer be able to ask for permission to directly access or control your Nest devices, thus keeping your data more private."
Since ThermoTweak works entirely by reading and sending commands to Nest Thermostats, it seems ThermoTweak will be going offline on August 31, 2019.
It's rather unfortunate (and shocking) that Google has taken the decision to allow third-party access to Nest Thermostats away from the consumer. It seems that Works with Google Assistant (the replacement for Works with Nest) will only allow apps to response to Google Assistant/Google Home prompts, which seems very limiting and a major step back in smart home technology.
I've heard from so many of you that ThermoTweak has been a huge improvement to your lives, which was extremely rewarding. I was very happy to have helped people work around some of the Nest's limitations. Thank you all for using and supporting ThermoTweak!
I'll keep ThermoTweak up and running as long as Google keeps the Nest API operating. (Again, it's scheduled to go offline on August 31.) In the meantime, I've disabled the Quarterly and Yearly subscriptions entirely. For new/renewing users who would like to continue using ThermoTweak, I've left the Monthly subscription enabled.