It is not a surprise to me that a week before Nikon announces their new full-frame mirrorless camera, Sony decided to publish a press release that they are now #1 in full-frame cameras with interchangeable lens sales (in both dollars and units) and that's only for the US market for the past 6 months:
Sony Electronics, Inc. – a worldwide leader in digital imaging and the world’s largest image sensor manufacturer – today announced that it has overtaken and held the No. 1 overall position in the United States full-frame interchangeable lens camera market in the first half of 2018, in both dollars and units. In fact, four out of every 10 full-frame cameras sold during this time period have come from the Sony brand.
The second paragraph is rather confusing to me - Sony claims the No. 1 position in the overall mirrorless market in both dollars and units for more than six years. Every other chart and ranking I have seen shows a different picture but this could be because some of the sources of the quoted data is "Sony internal historical data sources":
Additionally, Sony has announced that within the overall mirrorless market, it has held the No. 1 position in both dollars and units for more than six years.
Note that the graph above shows growth in %, and not market share or a comparison with other brands (obviously Sony had a big growth because they started from zero).
A reminder that in the past 12 months Sony announced two full frame cameras, Nikon had one and Canon had none. In the past 6 months, Nikon and Canon did not have any new full frame cameras while Sony had one.
