The latest beta is mIRC v7.45.438 and it can be downloaded from here
Beta 7.45.438 changes:
1.Item 1, updated.
2.Item 2, -h should be several times faster.
3.Item 3, also used internally.
4.Item 4, now uses CopyFileEx().
5.Item 5, now uses MoveFileEx().
6.Item 6, needs further testing to ensure no side-effects.
7.Item 7, also makes sure temp file does not already exist.
8.Item 8, settings retained if connected.
9.Item 9, fails if any folder in path cannot be created.
10.Item 10, now uses MoveFileEx().
11.Item 11, required changes to hotlinks and URL catcher.
12.Item 12, adds support for  brackets, eg http://[...].
1.Updated to OpenSSL 1.0.2h library.
2.Fixed /timer -h high resolution timer which was being limited to the
same rate as the -m millisecond timer.
3.Added $samepath(path1,path2) identifier that returns $true/$false
if paths refer to the same file/dir. It resolves relative paths and
converts long/short filenames.
4.Added /copy -f switch to flush copy to disk immediately.
5.Added /rename -f switch to flush rename to disk immediately and -o
switch to allow overwrite of an existing file.
6.Extended $calc() and other identifiers to return up to 14 decimal
digits in floating point calculations.
7.Added $tempfn identifier that returns temporary filename located in
mIRC folder using same method that mIRC uses internally.
8.Fixed Clear History bug that incorrectly cleared channels list
settings while status window was connected to a server.
9.Extended /mkdir to create the full path to the target folder.
10.Changed the way files are replaced during updates to decrease the
potential for file loss eg. lost mirc.ini files in situations such
as crashes, BSODs, and power failures.
11.Changed URL catcher to extract URLs using the same method used by
hotlink feature for consistency.
12.Extended URL hotlink/extract feature to handle IPv6 addresses.