diff --git a/.circleci/config.yml b/.circleci/config.yml
index d4cfbc950..552fa884c 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -62,7 +62,7 @@ jobs:
     - run:
         # Temporary workaround until circleci updates go.
         command: |
-          choco upgrade -y golang
+          choco upgrade -y golang --version=1.15.8
     - run:
         command:
           refreshenv
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8a105a702..fb035a12c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,8 +1,13 @@
-## 2.25.0-rc.0 / 2021-02-12
+## 2.25.0 / 2021-02-17
 
 This release includes a new `--enable-feature=` flag that enables
 experimental features. Such features might be changed or removed in the future.
 
+In the next minor release (2.26), Prometheus will use the Alertmanager API v2.
+It will be done by defaulting `alertmanager_config.api_version` to `v2`.
+Alertmanager API v2 was released in Alertmanager v0.16.0 (released in January
+2019).
+
 * [FEATURE] **experimental** API: Accept remote_write requests. Behind the --enable-feature=remote-write-receiver flag. #8424
 * [FEATURE] **experimental** PromQL: Add '@ <timestamp>' modifier. Behind the --enable-feature=promql-at-modifier flag. #8121 #8436 #8425
 * [ENHANCEMENT] Add optional name property to testgroup for better test failure output. #8440
@@ -15,6 +20,7 @@ experimental features. Such features might be changed or removed in the future.
 * [ENHANCEMENT] TSDB: Reload blocks every minute, to detect new blocks and enforce retention more often. #8343
 * [BUGFIX] API: Fix global URL when external address has no port. #8359
 * [BUGFIX] Backfill: Fix error message handling. #8432
+* [BUGFIX] Backfill: Fix "add sample: out of bounds" error when series span an entire block. #8476
 * [BUGFIX] Deprecate unused flag --alertmanager.timeout. #8407
 * [BUGFIX] Mixins: Support remote-write metrics renamed in v2.23 in alerts. #8423
 * [BUGFIX] Remote: Fix garbage collection of dropped series in remote write. #8387
diff --git a/VERSION b/VERSION
index 0257f1b3f..5c18f9195 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-2.25.0-rc.0
+2.25.0
diff --git a/cmd/promtool/backfill.go b/cmd/promtool/backfill.go
index 6e7a98c55..b04fb8b55 100644
--- a/cmd/promtool/backfill.go
+++ b/cmd/promtool/backfill.go
@@ -93,7 +93,13 @@ func createBlocks(input []byte, mint, maxt int64, maxSamplesInAppender int, outp
 		nextSampleTs = math.MaxInt64
 
 		err := func() error {
-			w, err := tsdb.NewBlockWriter(log.NewNopLogger(), outputDir, blockDuration)
+			// To prevent races with compaction, a block writer only allows appending samples
+			// that are at most half a block size older than the most recent sample appended so far.
+			// However, in the way we use the block writer here, compaction doesn't happen, while we
+			// also need to append samples throughout the whole block range. To allow that, we
+			// pretend that the block is twice as large here, but only really add sample in the
+			// original interval later.
+			w, err := tsdb.NewBlockWriter(log.NewNopLogger(), outputDir, 2*blockDuration)
 			if err != nil {
 				return errors.Wrap(err, "block writer")
 			}
diff --git a/cmd/promtool/backfill_test.go b/cmd/promtool/backfill_test.go
index 56c3cf70c..05b701a0b 100644
--- a/cmd/promtool/backfill_test.go
+++ b/cmd/promtool/backfill_test.go
@@ -365,6 +365,51 @@ http_requests_total{code="400"} 1 1565166113.989
 				},
 			},
 		},
+		{ // For https://github.com/prometheus/prometheus/issues/8476.
+			ToParse: `# HELP http_requests_total The total number of HTTP requests.
+# TYPE http_requests_total counter
+http_requests_total{code="200"} 1021 0
+http_requests_total{code="200"} 1022 7199
+http_requests_total{code="400"} 1023 0
+http_requests_total{code="400"} 1024 7199
+# EOF
+`,
+			IsOk:                 true,
+			Description:          "One series spanning 2h in same block should not cause problems to other series.",
+			MaxSamplesInAppender: 1,
+			Expected: struct {
+				MinTime   int64
+				MaxTime   int64
+				NumBlocks int
+				Samples   []backfillSample
+			}{
+				MinTime:   0,
+				MaxTime:   7199000,
+				NumBlocks: 1,
+				Samples: []backfillSample{
+					{
+						Timestamp: 0,
+						Value:     1021,
+						Labels:    labels.FromStrings("__name__", "http_requests_total", "code", "200"),
+					},
+					{
+						Timestamp: 7199000,
+						Value:     1022,
+						Labels:    labels.FromStrings("__name__", "http_requests_total", "code", "200"),
+					},
+					{
+						Timestamp: 0,
+						Value:     1023,
+						Labels:    labels.FromStrings("__name__", "http_requests_total", "code", "400"),
+					},
+					{
+						Timestamp: 7199000,
+						Value:     1024,
+						Labels:    labels.FromStrings("__name__", "http_requests_total", "code", "400"),
+					},
+				},
+			},
+		},
 		{
 			ToParse: `no_help_no_type{foo="bar"} 42 6900
 # EOF
diff --git a/docs/disabled_features.md b/docs/disabled_features.md
index 7c1c6e09e..ec6363451 100644
--- a/docs/disabled_features.md
+++ b/docs/disabled_features.md
@@ -16,7 +16,7 @@ They may be enabled by default in future versions.
 `--enable-feature=promql-at-modifier`
 
 The `@` modifier lets you specify the evaluation time for instant vector selectors,
-range vector selectors, and subqueries. More details can be found [here](querying/basics.md#-modifier).
+range vector selectors, and subqueries. More details can be found [here](querying/basics.md#modifier).
 
 ## Remote Write Receiver