The current required minimum for info::device::max_mem_alloc_size is:

Returns the maximum size of memory object allocation in bytes. The minimum value is max (1/4th of info::device::global_mem_size,12810241024) if this SYCL device is not of device type info::device_type::custom.

I suspect this definition came from OpenCL 1.2, which had the same definition for CL_DEVICE_MAX_MEM_ALLOC_SIZE.

The definition in OpenCL 2.0 and newer though is:

Max size of memory object allocation in bytes. The minimum value is max(min(1024 × 1024 × 1024, 1/4th of CL_DEVICE_GLOBAL_MEM_SIZE), 32 × 1024 × 1024) for devices that are not of type CL_DEVICE_TYPE_CUSTOM.

Note that this caps the minimum at 1GB.

Should the SYCL minimum have the same 1GB cap? Or is the difference intentional, and the SYCL minimum should be 1/4 of the total global memory size, even when the total global memory size exceeds 4GB?