This is xnu-4903.221.2. See this file in:
Directory listing for xnu-4903.221.2//config
BSDKernel.arm.exports
BSDKernel.arm64.exports
BSDKernel.exports
BSDKernel.x86_64.exports
IOKit.arm.exports
IOKit.arm64.exports
IOKit.exports
IOKit.x86_64.exports
Libkern.arm.exports
Libkern.arm64.exports
Libkern.exports
Libkern.x86_64.exports
MACFramework.arm.exports
MACFramework.arm64.exports
MACFramework.exports
MACFramework.x86_64.exports
MASTER
MASTER.arm
MASTER.arm64
MASTER.arm64.bcm2837
MASTER.x86_64
Mach.arm.exports
Mach.arm64.exports
Mach.exports
Mach.x86_64.exports
Makefile
MasterVersion
Private.arm.exports
Private.arm64.exports
Private.exports
Private.x86_64.exports
README.DEBUG-kernel.txt
System.kext/
Unsupported.arm.exports
Unsupported.arm64.exports
Unsupported.exports
Unsupported.x86_64.exports
Unused.exports
generate_linker_aliases.sh
generate_linker_exports.sh
list_supported.sh
newvers.pl
version.c