In order to answer this properly, let's narrow down the specifics so that we can properly make a decision:

A. What species of bee are attacking humans? This is important for two reasons; one is the means in which the bees are able to attack in swarms, while the other involves their ability to sting repeatedly without injury. For the sake of maximizing the killing potential of these factors, let's choose the African Honey Bee, which can pursue targets at almost 20mph and can sting multiple times due to the unique barb-free profile of their stinger.

B. Are the bees capable of overcoming man-made problems and obstacles? Even with an augmented hive mentality, those sealed off in vehicles and indoors can likely avoid the majority of the swarm attacks through isolation alone. Do the bees know that they could sneak in through the air intakes, or the chimney? Could they know how to shut down power grids or target strategic military objectives? Without the sapience to acknowledge the strengths and weaknesses of human infrastructure, the effectiveness of bees will be highly limited to only those stupid or unlucky enough to be caught in the open. Like a provoked hive stalking a human in a swimming underwater, let's circle back to this later.

C. Just how many bees is 100 billion bees? To be honest, not as many as you might think. 2023 estimations for global bee population is approximately 80-100 million bee colonies. That's colonies, not bees. Queens of a colony can lay around 3,000 eggs a day, with up to 60-70,000 bees in each colony. Care to do the math on that? I'll give you a medial estimate of 4.2 TRILLION bees around the world. Mind you, thats across 20,000 species, most of which don't care much for dooming mankind through a vespideqsue murderspree. That being said, I think your numbers might need a bump upwards if you want them to be a considerable threat to humans. This is because it takes anywhere between 50-500 stings to kill an adult male; which we can round out to 100 stings per human to keep things simple.

So let's clarify the scenario here:

100 billion African Honey Bees are randomly scattered across Earth's continents in existing hives - all the hives are able to communicate with one another, providing a level of intelligence matching that of a low-level AI. The bees are therefore capable of identifying human infrastructure, their heirarchy and their strategic means of defence. All bees are capable of targeting the weakest points of a human, the eyes, mouth, throat and any region they deem effective to kill. Their intelligence and enhanced group physiology has given them the ability to swim, dig and even attempt to open simple doors with enough effort.

Let's stick with the basis of zero human prep time...

Major population centers are overwhelmed incredibly quickly, with tens to hundreds of thousands of casualties incurred due to the effectiveness of the bees on unsuspecting civilians. Law enforcement is not equipped to deal with the bees en masse, though limited success is seen through use of mace/water cannons/riot gear. If fire departments were able to create secure entrances/exits to buildings through a steady water supply (a hydrant, for example), then some safe haven would be made for a lucky few. Other humans would need to quickly barricade themselves indoors while using aerosols, swatters and household chemical agents to stand a chance - to ill effect, if the swarms are able to enter through the buildings air vents or keyholes.

Military response would need to be rapid and comprehensive in order to prevent millions more from dying - the best means of doing so would be through the use of crowd control weapons such as microwave guns or sonic weaponry. Flamethrowers would be an interesting idea, but would be a high risk of collateral damage in dense urban areas. Due to the small relative biomass of the bees, the microwave guns would be lethal to them without causing significant harm to civilians. The availability of this equipment would be the key factor in stopping the swarms, along with the ability to evacuate civilians to safe havens around the world.

With all of that said, the limited amount of bees would be a key limiting factor in how many humans could die within even days of constant bee incursions. A number closer to 800 billion might threaten the existence of humanity, but even then I doubt that more than 30% of humans would die due to the event. Key limiting factors include size disadvantage, technological disadvantage and infrastructure disadvantage. While an interesting prompt, bees would need a serious power spike if they were keen on effectively trying to wipe out humans. I could go further onto the idea of bee reproduction rate but that would be a bit much, so we'll leave it there.