chore(main): release 1.6.1 (#2064)

🤖 I have created a release *beep* *boop*
---


##
[1.6.1](v1.6.0...v1.6.1)
(2026-04-27)


### Bug Fixes

* Preserve original metric names in OM2 output
([#2058](#2058))
([59a7a6d](59a7a6d))


### Documentation

* clarify 1.6.0 release notes
([#2062](#2062))
([9e5d591](9e5d591))
* Document semantic PR title guidance
([#2060](#2060))
([7277889](7277889))

---
> [!IMPORTANT]
> Close and reopen this PR to trigger CI checks.

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Gregor Zeitlinger <gregor.zeitlinger@grafana.com>

Author: github-actions[bot]

.github/config/.release-please-manifest.json

@@ -1,3 +1,3 @@
 {
-  ".": "1.6.0"
+  ".": "1.6.1"
 }

CHANGELOG.md

@@ -1,8 +1,37 @@
 # Changelog
 
+## [1.6.1](https://github.com/prometheus/client_java/compare/v1.6.0...v1.6.1) (2026-04-27)
+
+> Note: With the OM2 metric-name preservation fix in this release, OpenMetrics 2.0 can now be
+> tested. It is still in progress and not ready for general use yet.
+
+### Bug Fixes
+
+* Preserve original metric names in OM2 output ([#2058](https://github.com/prometheus/client_java/issues/2058)) ([59a7a6d](https://github.com/prometheus/client_java/commit/59a7a6d4d5a9eb31c33167764b11ba96d6625b74))
+
+
+### Documentation
+
+* clarify 1.6.0 release notes ([#2062](https://github.com/prometheus/client_java/issues/2062)) ([9e5d591](https://github.com/prometheus/client_java/commit/9e5d591f4c2e8e0d39ce5141ac14fff057b09c67))
+* Document semantic PR title guidance ([#2060](https://github.com/prometheus/client_java/issues/2060)) ([7277889](https://github.com/prometheus/client_java/commit/727788942cccbecfa57d75eee9fb3e942083a95e))
+
 ## [1.6.0](https://github.com/prometheus/client_java/compare/v1.5.1...v1.6.0) (2026-04-25)
 
 > Note: OpenMetrics 2.0 support is still in progress and not ready for general use yet.
+>
+> As part of the OM2 work, metric-name suffix handling moved from metric creation time to scrape
+> time. A positive side effect is that metric names are now more flexible across the board, for
+> example names ending in suffixes like `_total` are accepted where they were previously rejected.
+> To keep the Prometheus and OM1 output unambiguous, the registry tracks claimed exposition names
+> and still rejects registrations that would collide at scrape time.
+>
+> | Example | Before 1.6.0 | Since 1.6.0 | Reason |
+> | --- | --- | --- | --- |
+> | `Gauge("foo_total")` | Rejected | Allowed | Not breaking because this previously failed at registration, so no working setup changes behavior, and safe because `_total` suffix expansion applies to counters, not gauges. |
+> | `Counter("events_total")` | Rejected | Allowed | Not breaking because the OM1 output is still `events_total`; only the builder now accepts the name. |
+> | `Gauge("foo_total")` + `Histogram("foo")` | Rejected | Allowed | Not breaking because this combination used to be blocked even though the exposed names do not overlap. |
+> | `Gauge("events_total")` + `Counter("events")` | Rejected | Rejected | Not breaking because the ambiguous OM1 output would still expose two `events_total` series. |
+> | `Gauge("foo_count")` + `Histogram("foo")` | Allowed | Rejected | Intentionally breaking because the old behavior could expose a conflicting `foo_count` name at scrape time. |
 
 ### Features
 

benchmarks/pom.xml

@@ -5,7 +5,7 @@
   <parent>
     <groupId>io.prometheus</groupId>
     <artifactId>client_java</artifactId>
-    <version>1.6.1-SNAPSHOT</version>
+    <version>1.6.1</version>
   </parent>
 
   <artifactId>benchmarks</artifactId>

docs/content/getting-started/registry.md

@@ -78,6 +78,26 @@ Counter eventsTotal2 = Counter.builder()
     .register(); // IllegalArgumentException, because a metric with that name is already registered
 ```
 
+## Suffix-Based Name Validation
+
+Suffix handling happens at scrape time. This makes metric names more flexible while keeping the
+exposed output unambiguous.
+
+The registry now tracks not only the metric names you register, but also the exposition names they
+would claim in OpenMetrics 1.x and Prometheus text format, such as `_total`, `_count`, `_sum`,
+`_bucket`, `_created`, and `_info`.
+
+This means names are accepted when they are safe, and combinations are rejected when they would
+collide at scrape time. The table below also shows the pre-1.6.0 behavior for comparison.
+
+| Example                                       | Before 1.6.0 | Current behavior | Why                                                                                               |
+| --------------------------------------------- | ------------ | ---------------- | ------------------------------------------------------------------------------------------------- |
+| `Gauge("foo_total")`                          | Rejected     | Allowed          | Safe because `_total` suffix expansion applies to counters, not gauges.                           |
+| `Counter("events_total")`                     | Rejected     | Allowed          | Safe because the OM1 output is `events_total`; the writer avoids double-appending `_total`.       |
+| `Gauge("foo_total")` + `Histogram("foo")`     | Rejected     | Allowed          | Safe because the exposed names do not overlap: `foo_total` vs `foo_bucket`/`foo_count`/`foo_sum`. |
+| `Gauge("events_total")` + `Counter("events")` | Rejected     | Rejected         | Rejected because both would expose `events_total` in OM1.                                         |
+| `Gauge("foo_count")` + `Histogram("foo")`     | Allowed      | Rejected         | Rejected because both would claim `foo_count` at scrape time.                                     |
+
 ## Validation at registration only
 
 Validation of duplicate metric names and label schemas happens at registration time only.

examples/example-custom-buckets/pom.xml

@@ -4,7 +4,7 @@
 
   <groupId>io.prometheus</groupId>
   <artifactId>example-custom-buckets</artifactId>
-  <version>1.6.1-SNAPSHOT</version>
+  <version>1.6.1</version>
 
   <properties>
     <maven.compiler.release>8</maven.compiler.release>

examples/example-exemplars-tail-sampling/example-greeting-service/pom.xml

@@ -4,7 +4,7 @@
 
   <groupId>io.prometheus</groupId>
   <artifactId>example-greeting-service</artifactId>
-  <version>1.6.1-SNAPSHOT</version>
+  <version>1.6.1</version>
 
   <properties>
     <maven.compiler.release>17</maven.compiler.release>

examples/example-exemplars-tail-sampling/example-hello-world-app/pom.xml

@@ -4,7 +4,7 @@
 
   <groupId>io.prometheus</groupId>
   <artifactId>example-hello-world-app</artifactId>
-  <version>1.6.1-SNAPSHOT</version>
+  <version>1.6.1</version>
 
   <properties>
     <maven.compiler.release>17</maven.compiler.release>

examples/example-exemplars-tail-sampling/pom.xml

@@ -4,7 +4,7 @@
 
   <groupId>io.prometheus</groupId>
   <artifactId>example-exemplars-tail-sampling</artifactId>
-  <version>1.6.1-SNAPSHOT</version>
+  <version>1.6.1</version>
   <packaging>pom</packaging>
 
   <name>Example - Exemplars with OpenTelemetry's Tail Sampling</name>

examples/example-exporter-httpserver/pom.xml

@@ -4,7 +4,7 @@
 
   <groupId>io.prometheus</groupId>
   <artifactId>example-exporter-httpserver</artifactId>
-  <version>1.6.1-SNAPSHOT</version>
+  <version>1.6.1</version>
 
   <properties>
     <maven.compiler.release>8</maven.compiler.release>

examples/example-exporter-multi-target/pom.xml

@@ -4,7 +4,7 @@
 
   <groupId>io.prometheus</groupId>
   <artifactId>example-exporter-multi-target</artifactId>
-  <version>1.6.1-SNAPSHOT</version>
+  <version>1.6.1</version>
 
   <properties>
     <maven.compiler.release>8</maven.compiler.release>