Announce additional planned breaking changes for Protocol Buffers v38 (2027 Q1).

content/news/2026-10-15.md

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+
+
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+title = "Changes Announced on October 15, 2026"
+linkTitle = "October 15, 2026"
+toc_hide = "true"
+description = "Changes announced for Protobuf on October 15, 2026."
+type = "docs"
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+
+The following sections cover additional planned breaking changes in the v38
+release, expected in 2027 Q1. These describe changes as we anticipate them being
+implemented, but due to the flexible nature of software some of these changes
+may not land or may vary from how they are described in this topic.
+
+## Changes in C++ {#cpp}
+
+### Remove NULL Termination in Descriptor Names
+
+Descriptor APIs that return `absl::string_view` will no longer guarantee null
+termination. The null terminators are being removed to achieve memory savings in
+descriptors.
+
+This change applies to descriptor methods that return `absl::string_view`.
+Callers must not assume that the pointer returned by `.data()` is
+null-terminated. If a null-terminated C-style string is required, callers should
+explicitly construct a `std::string` (for example, `std::string(desc->name())`)
+or migrate to APIs that accept `absl::string_view` directly.
+
+## Changes in Protoc {#protoc}
+
+### Disallow Conflicting Descriptors in `--descriptor_set_in`
+
+Protoc will error when conflicting file descriptors are provided via
+`--descriptor_set_in`.
+
+Protoc introduced a warning when conflicting descriptors are detected across
+input sets. In the v38 release, this warning becomes an error. Build systems and
+callers must ensure that descriptor sets fed to `--descriptor_set_in` do not
+provide conflicting definitions for the same `.proto` file.
+
+## Changes in Python {#python}
+
+### Align `__eq__()` with `Any` Fields on Pure Python with Py-upb Behavior
+
+Align pure PythonProto `__eq__()` behavior to upb by only comparing the
+serialized bytes. There are some edge cases where two `Any` fields may contain
+different bytes which are equal only when parsed. These cases used to return
+`true`, but will now return `false`.
+
+## Changes in UPB {#upb}
+
+### Align Default Value Float and Double Formatting with C++ `FileDescriptor::CopyTo`
+
+In `upb_FileDef_ToProto`, `float` and `double` default values in
+`FieldDescriptorProto.default_value` were previously formatted using hardcoded
+`"%.9g"` and `"%.17g"`. This could produce more digits than C++
+`FieldDescriptor::DefaultValueAsString()` (`io::SimpleFtoa` / `io::SimpleDtoa`),
+causing `upb_FileDef_ToProto` output to differ from C++ `FileDescriptor::CopyTo`
+(for example, `"0.10000000000000001"` vs `"0.1"` for `double`, and
+`"7.77777779e+35"` vs `"7.777778e+35"` for `float`).
+
+In v38, `upb_FileDef_ToProto` will format `float` and `double` default values
+using round-trip formatting matching `io::SimpleFtoa` and `io::SimpleDtoa`.

content/news/_index.md

@@ -20,6 +20,8 @@ New news topics will also be published to the
 The following news topics provide information in the reverse order in which it
 was released.
 
+*   [October 15, 2026](/news/2026-10-15) - Additional
+    breaking changes in the upcoming 38.x release
 *   [September 22, 2026](/news/2026-09-22) - Breaking
     changes in the upcoming 38.x release
 *   [July 13, 2026](/news/2026-07-13) - Edition 2026