pypi / pymongo

pymongo

What changed in pymongo 4, from its official release notes, upgrade guides and advisories. Sources checked 2026-10-22.

3 breaking4 security2 deprecations1 new APIs and options3 performance3 behavior and defaults3 fixes and other

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pymongo 419 changes

Client-side field level encryption now rejects KMS endpoints ending in .sock.
4.18.2release notes security advisory
Support for MongoDB 4.2 was dropped.
4.18.0release notes
Server selection deprioritization now applies only to overload errors on replica sets.
4.17.0release notes

The release notes reference CVE-2026-106435 but provide no details about the security change.
4.18.3release notes
PyMongo: PYTHON-5986 Host injection in PyMongo connection string parsing via percent-encoded delimiters
4.18.2security advisory release notes
PyMongo: PYTHON-5996 Heap out-of-bounds write via signed size overflow in BSON document encoding
4.18.2security advisory release notes
GridFS delete_many now matches the file ID exactly, fixing inexact matches.
4.18.1release notes security advisory

PyPy support is deprecated and will be removed in a future release.
4.18.0release notes
Python 2 methods in SON are deprecated.
4.17.0release notes

Added as a URI option and MongoClient keyword argument; for mongodb+srv:// connections, it allows SRV-returned hosts under a different domain suffix, provided the suffix is not a public suffix.
4.18.0release notes

Improved MongoDB 9.0’s IWM performance by retrying overload errors only when doing so is not expected to worsen server conditions.
4.18.0release notes
TLS sessions are reused across connections to the same server to improve connection performance.
4.18.0release notes
BSON encoding and decoding performance improvements may benefit applications that process BSON data.
4.17.0release notes

General availability support was added for prefix, suffix, and substring queries against MongoDB 9.0+; requires libmongocrypt 1.20.0 or later.
4.18.0release notes
Simple collation is now included in index information.
4.17.0release notes
The callback type now accepts the broader Awaitable type rather than only Coroutine objects.
4.15.4release notes

Added support for MongoDB 9.0.
4.18.0release notes
The sessions API was improved; the notes do not specify the details.
4.17.0release notes
Fixes a bug that could cause AutoReconnect("connection pool paused") errors when cursors fetched more documents after SDAM heartbeat failures.
4.15.5release notes