Chromecast is a digital media player used to stream audio-visual content on a HDTV developed by Google.

Google released 1st generation in 2013 and second generation 2015 which is the current model.

Google Is Working On A Chromecast To Provide Bluetooth and Strong Wi-Fi Connectivity.

It was already known that Google was working on a refreshed model, but now list from FCC provides additional detail about the product.

According to the listing, the new Chromecast will support Bluetooth connectivity, the first one to support Bluetooth. The current 2nd Generation doesn’t have Bluetooth chip.
The FCC documentation also revealed that :

Google was thinking to update current software to enable the Bluetooth legacy operations and current product is approved under A4RNC2-6A5.
The enable Bluetooth legacy a software change has been implemented but it requires a new equipment code (DSS) which is not covered by the original certification and new product requires a new FCC ID.
The Device bearing FCC ID A4RNC2-6A5 will not receive any software update to enable legacy Bluetooth operations.

According to the new documentation, there will be one hardware change:

The device now includes a 0.5nm trim 5GHz PGB antenna trace that increases the 5GHz maximum antenna gain from 2.1dBi to 4dBi. it means that along with the Bluetooth Chromecast will also offer improved Wi-Fi reception with 5GHz networks. Since the design is identical it is possible the new Chromecast will make its debut in a hardware event on Oct 4 to replace the 2015 Chromecast.