Compared to the Tamron:
Sony FE 100-400mm GM OSS F4.5-F5.6 (2700 euros) : Similar Sharpness performances but better AF for erratic movements and compatible with TC1.4 TC2.0 and 30fps of the A1, more buttons for direct controls , but more heavy and pricy. Less versatile as 100mm is often too long for some portraits or street photography