Three models have been shipped. They have no feature differences, only a different connection for the on-board LED.
You can identify your model by the presence of “rev2”, “rev4”, or nothing on the top (the side with the gold connectors) of the USB end of the Digispark. Also, there is a “rev3” version in circulation; this is actually countefeit (i.e. a clone which falsely uses the Digispark trade name), although functionally it seems to match the (true) revisions 2 and 4.
Rev2 or Rev4 marking: The on-board LED is connected to P1 This board should cause no conflicts with any devices, but remember the LED is on pin 1 not pin 0!
No marking: The on-board LED is connected to P0 This board requires the trace to the LED to be cut (or the LED desoldered) if you'd like to use it with I2C devices.
We recommend using an exact-o knife or similar small sharp blade. The area that needs to be scored or cut is outlined with a white box on the board - highlighted in red below for clarity.
To reconnect the LED for non I2C use, one can solder across the white box from the led to the closest pin of the IC.