From Trans Athelete - Scroll down to International Olympic Committee

International Olympic Committee (IOC) Consensus Meeting in November 2015 agreed the following guidelines to be taken into account by sports organizations when determining eligibility to compete in male and female competition:

1. Those who transition from female to male are eligible to compete in the male category without restriction.
2. Those who transition from male to female are eligible to compete in the female category under the following conditions:
   1. The athlete has declared that her gender identity is female. The declaration cannot be changed, for sporting purposes, for a minimum of four years.
   2. The athlete must demonstrate that her total testosterone level in serum has been below 10 nmol/L for at least 12 months prior to her first competition (with the requirement for any longer period to be based on a confidential case-by-case evaluation, considering whether or not 12 months is a sufficient length of time to minimize any advantage in women’s competition).
   3. The athlete's total testosterone level in serum must remain below 10nmol/L throughout the period of desired eligibility to compete in the female category.
   4. Compliance with these conditions may be monitored by testing. In theevent of non-compliance, the athlete’s eligibility for female competition will be suspended for 12 months.

So MtT people will have to have a testosterone level below 10nmol/l

Update: From Guardian Report New IAAF testosterone rules could slow Caster Semenya by up to seven seconds

“The other really interesting thing is that, guided by the new IOC transgender policy that lowers the upper limit for testosterone to 5nmol/L, the IAAF are setting their limit at 5nmol/L. It used to be 10. That will slow the times of these athletes down even more than it did in the past.”

Testosterone levels can be expressed in different units. This handy tool https://www.nebido.com/tools/index.php/en/default/index/conversion-tool makes it easy to compare

10 nmol/L is the same as 288 ng/dl 5 nmol/L is the same as 144 ng/dl

from http://www.healthline.com/health/low-testosterone/testosterone-levels-by-age#Adolescence3

Men can compete as women if their T level is 144 ng/dl

Which is 2 times higher than the top of the normal level for women. It is also higher than the lower level for 16 year old boys.

Men can compete against women, by declaring that they are women and having a testosterone level 2 times higher than women. They might not even have to take any hormone changing drugs