Is Monero ASIC resistant? If not, are there already people out there running on ASICs?
Cryptonight (the PoW hash used by Monero and most Cryptonote coins) does not lend itself well to ASIC development, for the following reasons:
Cryptonight requires 2 MB of fast memory to work. This means that parallelizing hashes is limited by how much memory can be crammed in a chip while keeping cheap enough to be worth it. 2 MB of memory takes a lot more silicon than the SHA256 circuitry, for instance.
Cryptonight was designed to take advantage of the AES-NI instruction set, which uses existing hardware circuitry on modern x86_64 CPUs to speed up AES operations (Cryptonight is based on AES, a modern symmetric cipher). This means that at least some of the work done by Cryptonight is already being done in hardware when run on modern consumer machines.
There has been some talk of replacing the PoW algorithm with Cuckoo Cycle (an alternative PoW hash designed to be ASIC resistant too, see details about it at https://github.com/tromp/cuckoo). If such a switch happened, the R&D cost of developing a Cryptonight ASIC would be lost in large part, since they could not be used for Monero anymore.
So, no, there are no ASICs for mining Monero as of now, and probably will not in the near future either.
Monero is not immune to ASICs in the future, but the costs of manufacturing ASICs is offset by the block rewards such that it would not be profitable. ASIC manufacturing would need to get cheaper, or the value of XMR would need to skyrocket for people to even consider ASIC mining. As I understand it, Monero's POW requires 2mb to perform hashing, and ASIC manufacture with high memory requirements can get very expensive, very fast. This means that off the shelf hardware like GPUs and CPUs still carry an advantage and probably will do for years to come.
No such thing as ASIC resistant, CryptoNight (the POW algorithm) requires 2 Mb per instance, this makes ASIC manufacturing expensive and thus discouraged for the time being ($2 USD per XMR)
Baikal has delivered an ASIC miner which is for sale on their web site here: http://www.baikalminer.com/product12.php
Bitmain Introduce Cryptonight ASIC
Monero's ideology is ASIC-resistance. This was previously done by adapting Cryptonight with each release making ASICs harder and harder - but Monero has now switched to pseudorandom program execution for hashing called RandomX.