It is New Year in Ethiopia, a modern republic and former ancient monarchy in the Horn of Africa that still follows the Julian calendar.

To celebrate, Abiy Ahmed, Ethiopia’s 42-year-old prime minister and the most dynamic leader in Africa, opened the frontier with old-enemy Eritrea, allowing families separated for a generation to pour across the border in tearful reunion.

These days, it feels like New Year in Ethiopia every day. Mr Abiy has been prime minister for less than six months, after the abrupt departure of his predecessor.

Such has been the thirst for political change that his ascendance, and the startling use he has made of his new-found authority, have been greeted with near-euphoria. Polls suggest he has a 90 per cent support rate.

People in a country with a median age of 19 snap up books about their new hero, the first prime minister drawn from the politically marginalised Oromo ethnic group. The Oromo make up about 35 per cent of the country’s swelling population of 105m.

Mr Abiy, a former army intelligence officer, speaks all three of the country’s main languages. His father was Muslim and his mother Christian. Educated in computer engineering in Addis Ababa, business studies at London’s University of Greenwich and with a doctorate in conflict resolution, Mr Abiy is an insider with an outsider’s perspective on his country’s complexities and contradictions.

The new prime minister has become a sort of cross between Che Guevara and Emmanuel Macron. Almost inevitably, his rise has spawned the term Abiymania. So far, despite an assassination attempt , Abiymania has not bitten the dust.

Since April, Mr Abiy has wasted no time. As well as concluding an undreamt-of peace deal with Eritrea, he has released thousands of political prisoners, legalised opposition parties, and eased restrictions on tight internet controls.

He has proposed opening the telecoms and airline sectors to foreign capital, a change that would breathe new life into an economy reaching the limits of state planning.

Mr Abiy has also begun to dismantle much of the state apparatus that had brought Ethiopia to the brink of political implosion.

The sudden resignation of his predecessor in February ended a period of popular revolt that had threatened to sweep away the Ethiopian People’s Revolutionary Democratic Front, the four-party coalition that had run the country since overthrowing the Marxist Derg in 1991.

The locus of that rebellion was Mr Abiy’s home state of Oromia. Though nominally part of the four-party coalition, the Oromo felt — in common with other ethnic groups — that the EPRDF placed too much power in the hands of Tigrayans, who comprised just 6 per cent of the population.

Under Tigrayan stewardship — some would say dictatorship — Ethiopia had embarked on one of Africa’s boldest experiments in social and economic transformation.

Modelling itself on successful Asian economies, the tight-knit leadership began to plot Ethiopia’s escape from poverty. It ran a ruthlessly centralised economy, funnelling scarce resources into state priorities including education, health, road, rail, electricity, dams and industrial parks.

The results have been impressive, particularly to an international community hungry for an African success story. Growth — at least officially measured — has regularly topped 10 per cent. Child mortality rates have plummeted.

But the political foundations on which Ethiopia’s experiment was built were crumbling. The EPRDF maintained power as much through repression as through social progress. It facilitated land grabs, often in Oromia, and was widely accused of corruption.

Tens of thousands of people were locked up. Hundreds were shot in the street. Many prisoners — as Mr Abiy daringly conceded in parliament — were tortured in what he likened to state-sponsored terrorism against its own people.

Mr Abiy’s rise to power looks like an attempt by the EPRDF to save its own skin and keep the experiment in social transformation going. But Mr Abiy has spent as much time challenging power structures as preserving them.

The era of Tigrayan domination is over. Ethiopia’s new leader has removed prominent Tigrayan figures, including the head of the army and the security services.

Last month, he cancelled a contract to install turbines for the $4.8bn Grand Ethiopian Renaissance Dam awarded to a military-run company with close links to the ruling elite.

Day by day, Mr Abiy is whittling down the political and economic power of the old guard. One danger is that he will be stopped. Another is that he will be corrupted by power and adulation. He would not be the first. But the story so far has been almost universally positive. The wonder is how on earth he is getting away with it.