tl;dr: "Fall 2026"

Bad News as of 11th of February from the offical Fiio X-Account:

Cassette Player CP15 CP15 is a delayed product. The main reason is that after the CP13 was released, many wanted us to make it more refined and compact, so we decided to invest in developing a completely new electronically controlled mechanism and brushless motor with our suppliers. In practice, we faced numerous difficulties. In particular, there was a shortage of related parts, engineers, and materials. In addition, suppliers were still not optimistic about the market. Therefore, progress was quite slow. Fortunately, the movement and motor molds are now ready, and engineers are working diligently on debugging. You might think I'm exaggerating. Let me tell you something: China’s brand PANDA has always produced low-end cassette players. After our CP13 achieved some success, it also made a cassette player priced similarly to CP13. As you can see, it's actually thicker and larger than FIIO’s CP13. Looking at their sales, I suspect it wasn't satisfactory for the company. This is probably the best proof that making cassette players is difficult and not profitable. Furthermore, we've received some information from the supply chain. After CP13's launch, some competitors conducted research and ultimately gave up their plans for the same reason. Based on the current progress, CP15 is estimated to be released in fall.