(Pocket-lint) - Microsoft has subtly upgraded the Core i5 processor inside the 13.5-inch Surface Book 2.

The addition of the $1,499 quad-core model uses Intel's latest-generation 8th generation Core i5-8350U clocked at 3.6Ghz. 

Other specs are unchanged, with 256GB of storage and 8GB of memory. While you can get away with less, we tend to recommend 256GB/8GB. 

It's not yet possible to specify the new model in the UK Microsoft Store, but it must be imminent as the option is displayed, but greyed out. 

We're not sure why Microsoft chose to do this quietly, especially as the new addition pushes the old version using Intel's dual-core 7th generation chip down to a much more palatable price point.The 128GB model using the older generation processor is $1,149 or £1,149 in the UK, while the 256GB model is $1,299

The move was first rumoured at the start of last month. 

We're expecting Microsoft's top-line convertible laptop to get a full refresh in October - that's when Microsoft has held a Surface launch event for the last couple of years.

However, with Intel's Ice Lake 10th generation processors set to debut at the end of the year, we could see the street date delayed a little. 

Writing by Dan Grabham.