Yes 2+2 cores, but the OS and applications only ever see 2 cores. A guy in another thread said he spoke with an Apple engineer, and apparently the Apple implementation is different than other implementations which usually depend on software to allocate workload to the various cores. Apple tested this and found it inefficient, similar to other implementations which have also been criticized for being inefficient in this aspect. So, in the case of A10 Fusion, it was engineered such that all workload is directed to the appropriate cores in hardware. This is invisible to the kernel and software.
Phil said that the power utilization of the 2 lightweight cores is roughly 20% of the power utilization of the main cores, so obviously there can be a huge power savings. Phil didn't say this, but interestingly, in most implementations, stuff like 1080p h.264 video playback is considered "light" usage (since it's all GPU accelerated anyway), so there can be decent power savings there. Same with stuff like checking email, etc.
The 8-core solutions from other companies have almost as good multi-core performance according to Geekbench 4, but the cores are much less powerful individually, so for single-threaded or poorly multi-threaded applications the Apple A10 would stomp them into the ground because the single-threaded performance is so high. In fact, Apple A10 is almost twice as fast in single-threaded work as compared to the nearest Android competitor. That would be Samsung Exynos 8890 (octo-core) which gets around 1800 single-core, compared to about 3400ish or so average for A10.
https://browser.primatelabs.com/android-benchmarks
Furthermore, as mentioned, the Android-oriented chip solutions are software managed for core switching and claimed to be less efficient.
For multi-core, the Android solutions are almost as fast, but since they require four cores to do it, again the issue of poorly multi-threaded applications rears its ugly head again. Poorly multi-threaded applications may be more efficient on two fast cores than four slow ones, and we already know that Geekbench 4 which has good multi-threading support, rates the two cores of A10 cumulatively slightly faster than the fastest Android competitor in multi-core work.
In terms of numbers:
Apple A10 Fusion gets about 1.6X single-core speed with two cores. That means about 5400 multi-core vs. 3400 single.
Samsung Exynos 8890 gets about 2.9X single-core speed with four cores. That means about 5300 multi-core vs 1800 single.
I'm not sure about clock speeds, but It's interesting to see that some of the Geekbench scores cluster around 2.33 GHz and 1.05 GHz. I wonder if these could be the actual operating frequencies of the two groups of A10 cores, or if these are just by chance. (Geekbench apparently doesn't directly measure clock speed apparently, and just estimates it, but sometimes incorrectly.)
It should be noted that Apple dabbled with more than 2 cores in my iPad Air 2's A8X, which is triple core. However, A9, A9X, and A10 are all back at 2 cores again.
Now, all that being said, one of the things I like most about the iPhone 7 Plus is its supposed 3 GB RAM. The 6 was lame with its 1 GB RAM, and the 6s was adequate with its 2 GB RAM. 3 GB seems appropriate (on iOS) in 2016, so one criticism I have is that the iPhone 7 non-Plus apparently didn't also get 3 GB. It's 2 GB RAM. People are speculating though that the iPhone 7 Plus gets 3 GB more for the dual-lens camera though, rather than anything else. (Remember that even the 9.7" iPad Pro only has 2 GB RAM.)
Overall, the star of the 2016 iPhone release is the iPhone 7 Plus. The 7 is iterative, yes with a faster SoC, but only the Plus is a genuine leap forward IMO with 3 GB RAM and a dual-lens camera. So, I ordered the 7 Plus (128 GB). It's due to arrive this week.