The 4.0.1 MongoDB Java & JVM Drivers release is a patch to the 4.0.0 release and a recommended upgrade.
Reference documentation
The documentation hub includes extensive documentation of the 4.0 driver, including
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What’s New: what’s new in the 4.0 driver
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Upgrading: upgrading from the 3.12.x driver
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Installation MongoDB Driver: how to get the Java driver.
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Installation MongoDB Reactive Streams Driver: how to get the Reactive Streams driver.
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Installation MongoDB Scala Driver: how to get the Scala driver.
and much more.
Bug fixes
You can find a full list of bug fixes here.