"Death's End" by Cixin Liu

The third volume of the "Remembrance of Earth's Past" or "The Three-Body Trilogy" is even grander in scale than the previous two volumes.  What began as a 'First Contact" novel has turned into a Space Opera of the grandest scale going all the way to the End of the Universe, billions of years in the future.

The book starts with a tidbit about the Fall of Constantinople and implications of 4-dimensional space, but the real action starts around the same time as the second volume.  At teh same time as teh "Wallfacer" project the UN starts another, "The Staircase" project, which sends a brain in a capsule that can achieve 1% of the speed of light through being propelled with Nuclear Bombs and Radiation Sail.  Qang Xin, is the main protagonis, a young, "classically beautiful" PhD in Rocket Propulsion, who works for the UN Intelligence Agency, created by the World Powers to figure out ways to counter the Tri-Solarians.

When she's awaken in the future, just when Luo Ji is about 100 years old, and needs to transfer the "Sword" to another "Swordholder" - she is elected by the population of the Earth,  The Trisolarians, through the one-dimensional Sophon AIs and the "Sophon" android they've created in the image of a perfect human female, have been feeding Humans false knowledge for a while, even though they were in the Deterrence Era, knowing that Luo Ji would activate "The Sword" and expose both planets to a Dark Forest attack and thus destruction.  However, as soon as Qang Xin take the sword, the Trisolarians attack the Earth's gravity wave transmission stations, with the droplets that were lying hidden in the Solar system, although humans were told that the droplets have been withdrawn.  The lying and deception of the Trisolarians has reached or surpassed human levels, even though they started from zero.  Trisolarians built a psychological profile of Qang Xin and knew she would not have the courage (or have too much love and mercy) to use the Sword.

Human fleet is destroyed, Android Sophon becomes a monster and herds all humans onto Australia ( billions of people) and then sarcastically tells them now they have to eat each other for food until only about 50 million are left, which are to be kept alive as zoo specimens when Trisolarians arrive.
However, one space ship, the "Gravity" manages to send the location message from outer space and suddenly Trisolarians turn around and head away from the Solar System, as it is now exposed to Dark Forest attack.  However, before the Solar System is destroyed, the Trisolarian planet and Sun is vaporized by a 'mass dot' or photoid attack, killing everyone on the planet except a thousand or so who were in space ships at the time hidden behind the other two suns in the system.  This is probably the most satisfying moment of the book, as the Trisolarian garbage gets what they deserve for fucking with the human race.

Nevertheless, the Solar System is destroyed eventually, with another type of attack, a real Dark Forest attack, with all humans in it, except for Qang Xin and A.A. who are the only to escape (not with the blessing of other humans. goes to prove that most humans are animals).  There's a gift of a star involved, and a curvature propulsion which reaches light speed, and a max-rational American who builds the greatest business empire known to man - only to be brought down by Qang Xin, and the consewuences of creating a "Dark Domain" where light speed it lowered to 16.7km/sec, and the time-flow implications, and mini-universes, and M-Theory branes, and enemies becoming friends again, at the end of time and existence, and a hope for a new, better universe, a "Garden of Eden" possibly with the original 10 dimensions in macroscopic reality, but that's all to be read and enjoyed again, one day.

I've never been so excited to read a science fiction trilogy since the days I first read teh Great Asimov's original "Foundation Trilogy".  Cixin Liu is a master of the art.  This is Hard Science Fiction in a form and vision which is as good as it gets.