Here's the part of the code that governs the amount of the block reward:
CAmount GetBlockSubsidy(int nPrevBits, int nPrevHeight, const Consensus::Params& consensusParams, bool fSuperblockPartOnly)
{
double dDiff;
CAmount nSubsidyBase;
// if (nPrevHeight <= 4500 && Params().NetworkIDString() == CBaseChainParams::MAIN) {
/* a bug which caused diff to not be correctly calculated */
// dDiff = (double)0x0000ffff / (double)(nPrevBits & 0x00ffffff);
// } else {
dDiff = ConvertBitsToDouble(nPrevBits);
// }
if (nPrevHeight < 5465) {
// Early ages...
// 1111/((x+1)^2)
nSubsidyBase = (1111.0 / (pow((dDiff+1.0),2.0)));
if(nSubsidyBase > 50) nSubsidyBase = 50;
else if(nSubsidyBase < 1) nSubsidyBase = 1;
} else if (nPrevHeight < 17000 || (dDiff <= 75 && nPrevHeight < 24000)) {
// CPU mining era
// 11111/(((x+51)/6)^2)
nSubsidyBase = (11111.0 / (pow((dDiff+51.0)/6.0,2.0)));
if(nSubsidyBase > 50) nSubsidyBase = 50;
else if(nSubsidyBase < 25) nSubsidyBase = 25;
} else {
// GPU/ASIC mining era
// 2222222/(((x+2600)/9)^2)
nSubsidyBase = (2222222.0 / (pow((dDiff+2600.0)/9.0,2.0)));
if(nSubsidyBase > 25) nSubsidyBase = 25;
else if(nSubsidyBase < 5) nSubsidyBase = 5;
}
// LogPrintf("height %u diff %4.2f reward %d\n", nPrevHeight, dDiff, nSubsidyBase);
CAmount nSubsidy = nSubsidyBase * COIN;
// yearly decline of production by ~7.1% per year, projected ~18M coins max by year 2050+.
for (int i = consensusParams.nSubsidyHalvingInterval; i <= nPrevHeight; i += consensusParams.nSubsidyHalvingInterval) {
nSubsidy -= nSubsidy/14;
}
// Hard fork to reduce the block reward by 10 extra percent (allowing budget/superblocks)
CAmount nSuperblockPart = (nPrevHeight > consensusParams.nBudgetPaymentsStartBlock) ? nSubsidy/10 : 0;
return fSuperblockPartOnly ? nSuperblockPart : nSubsidy - nSuperblockPart;
}
We appear to be in what the developer labeled in comments as the "GPU/ASIC mining era".
The exact amount is governed by current difficulty level, but at the current block height it cannot be more than 25, and can go as low as 5.