The best I have been able to do on my Blackboard is 1.63 uA at 3.3V. That is based on:
See this post viewtopic.php?p=208415#p208415 to see a table of power consumption data.
It’s all moot though because none of the A1 processors can reliably reach these current levels. As mentioned in this post viewtopic.php?p=208325#p208325, the A1 processors have a bug that comes into play when they are in deep sleep. According the Ambiq, the SIMOBUCK voltage regulator on an A1 can lock up and fail, eventually causing the ASIC to suffer a supply voltage brownout reset. The published workaround from Ambiq is to never let the A1 chip go into deep sleep. That is accomplished by leaving the PDM unit turned on because it takes the least current of any peripheral on the chip. You can see that inside the HAL routine am_hal_pwrctrl_low_power_init() where the code explicitly tests if the processor is an A1 with the SIMOBUCK turned on and if so, turns on the PDM to avoid triggering the bug.
On my Blackboard with its A1 silicon, it means that the deep sleep current I have measured is more like 38.0 uA, as per my current consumption chart mentioned earlier in this post. The only way to get a reliable 1.63 uA deep sleep is via B0 silicon. I have asked if there is a plan to release boards with B0 silicon on them in this post viewtopic.php?p=208325#p208325, but have not heard back from Sparkfun yet. Maybe you can ask around for us!!