Here is a more detailed description which is a public statement direct from Tandem.
Basal-IQ Technology uses a simple linear regression algorithm that predicts glucose levels 30 minutes ahead based on 3 of the last 4 last consecutive CGM readings. If the glucose level is predicted to be less than 80 mg/dL, or if a CGM reading falls below 70 mg/dL, insulin delivery is suspended. Insulin delivery resumes as soon as sensor glucose values begin to rise. Insulin may be suspended for a minimum of 5 minutes and a maximum of 2 hours within a 2.5-hour rolling window.
Additionally:
… insulin delivery can resume with first upward CGM reading.
Although we would likely use this 24x7 unless we specifically see an issue, the biggest benefit is certainly expected to be nighttime. I plan to get the Tandem Basal-IQ update as soon as it is released (which I believe is Monday) and we get our email (which will be staggered across the X2 population of users to prevent an unmanageable surge on Monday for Customer Service and the download servers).
However I do not expect to switch over to the G6 (from the G5) until the Sept/Oct timeframe so it is unlikely we will be able to immediately make use of the update. Tandem Customer Support specifically told me we would NOT be able to use the update with the G5. No reason not to try it anyhow.
Well - one reason perhaps.
If somebody wanted to keep running their X2 in integrated mode with their G5 would be a reason NOT to apply the Basal-IQ update. According to Tandem Customer Support (as mentioned), the update will prevent the G5 from connecting to the X2. As well, the update is NOT able to be rolled back by the customer.