namespace std::chrono {
class tai_clock {
public:
using rep = *a signed arithmetic type*;
using period = ratio<*unspecified*, *unspecified*>;
using duration = chrono::duration<rep, period>;
using time_point = chrono::time_point<tai_clock>;
static constexpr bool is_steady = *unspecified*;
static time_point now();
template<class Duration>
static utc_time<common_type_t<Duration, seconds>>
to_utc(const tai_time<Duration>&) noexcept;
template<class Duration>
static tai_time<common_type_t<Duration, seconds>>
from_utc(const utc_time<Duration>&) noexcept;
};
}

The clock tai_clock measures seconds since 1958-01-01 00:00:00
and is offset 10s ahead of UTC at this date.

That is, 1958-01-01 00:00:00 TAI is equivalent to 1957-12-31 23:59:50 UTC.

Leap seconds are not inserted into TAI.

Therefore every time a leap second is inserted into UTC,
UTC shifts another second with respect to TAI.

For example by 2000-01-01 there had been
22 positive and 0 negative leap seconds inserted
so 2000-01-01 00:00:00 UTC is equivalent to 2000-01-01 00:00:32 TAI
(22s plus the initial 10s offset).