Stand behind a line of photographers pointed at something offshore and you can price the whole row without asking a single question. Two or three big white primes, a handful of black consumer superzooms, at least one lens discontinued before mirrorless existed. One person has a monopod planted in the sand and the rest are holding everything up with their arms. They are all framing the same subject at roughly the same size.

Sony already sells a 100-400mm. The GM version has been around since 2017, weighs about 1,395g, and still asks roughly $2,500. The new SEL100400 covers the identical focal range at 654g and $849.99, shipping in September. Canada gets it at $1,079.99. The money came out of the aperture. The GM opens at f/4.5-5.6. This one starts at f/5.6 and closes to f/8 by the long end. That is the whole trade, and whether it matters depends entirely on where you shoot.