diff --git a/tests/perf/query_cases/promql_series_rate_fusion/README.md b/tests/perf/query_cases/promql_series_rate_fusion/README.md
new file mode 100644
index 00000000000..86d6d9fef93
--- /dev/null
+++ b/tests/perf/query_cases/promql_series_rate_fusion/README.md
@@ -0,0 +1,50 @@
+# PromQL series rate-fusion regression fixture
+
+This native Query Regression case isolates the candidate shape `SUM(Float64)` by
+`dc` over one direct `prom_rate` expression, projected as Float64 with a
+millisecond timestamp and zero offset. The immutable input uses the previously qualified dictionary-tag A direct-SST
+generator, schema, and layout. All parameters are specified in this case; no
+private or gitignored source file is required. It uses seed 25652, 4,096
+instances × 512 samples = 2,097,152 rows, 16 `dc` values, 4 devices, and two flat
+non-overlapping SSTs of 1,048,576 rows each, 8,192-row groups, 15-second
+millisecond timestamps, primary key `(instance, dc, device)`, and deterministic
+wave values from 0 through 100. It uses the same data generator, not the
+original 127-slope counter or an archived original input.
+
+The range window is 1704069900–1704071715 seconds at 15-second steps (122
+evaluations), fully covered by fixture timestamps from 1704067200 through
+1704074865. The first SST ends at 1704071025; the 5-minute lookback begins at
+1704069600, so this range crosses the actual two-SST boundary and requests data
+from both files. Actual scanned row counts must be audited from runtime plans;
+the full 2,097,152-row fixture size is not an expected scan count for this query.
+The primary range query expects 16 `dc` output groups per evaluation (1,952
+result rows) and evaluates 4,096 series per evaluation (499,712
+evaluation-points). The instant query at 1704071715 expects 16 output rows.
+Primary `TQL EVAL` entries preserve complete response data and use 3 warmups/20
+range iterations and 3 warmups/9 instant iterations; the range EVAL is also the
+runner's untimed first-query validation. Separate one-shot `TQL ANALYZE VERBOSE`
+entries capture runtime gate, actual plan, scan/index, and work-count diagnostics
+without adding analyze overhead to timed samples. An untimed one-iteration SQL
+audit returns one row per `dc`, verifying 131,072 rows and 256 instances per
+group and min/max timestamps 1704067200 and 1704074865.
+
+Controls are limited to grouped `sum_over_time` (wider non-rate path),
+grouped `min by (dc) (rate(...))` (a different aggregation operator and a
+negative fusion-gate control), and grouped `rate` with a 15-second offset
+(offset gate). MIN keeps the same range, rate-window work, and compact 1,952-row
+answer while not matching the SUM candidate. They reuse the same table and
+range. The offset query's parser acceptance must be confirmed on the pinned
+runtime. Each timed query retains the existing 10% candidate-latency-regression
+threshold: a pass only means that configured guard did not trip; it is not proof
+of candidate-gate activation or performance improvement. Do not loosen it to
+hide noise.
+
+After a native run, audit the normalized plans and complete raw responses,
+including group labels, timestamps, numeric values with appropriate floating
+point tolerance, and expected row counts. Also audit source SHAs, compiler,
+features, fixture layout, the actual runtime gate, scans/indexes, and work counts.
+Official performance acceptance still needs clean base/candidate medians,
+control behavior, drift and tolerance review, and complete cross-arm answers.
+This fixture alone cannot establish a gain. Finite-pool behavior, drops, and
+spill behavior belong to code tests, not this CI case. No official workflow was
+run as part of adding this fixture.
diff --git a/tests/perf/query_cases/promql_series_rate_fusion/case.toml b/tests/perf/query_cases/promql_series_rate_fusion/case.toml
new file mode 100644
index 00000000000..3eb5a1998a3
--- /dev/null
+++ b/tests/perf/query_cases/promql_series_rate_fusion/case.toml
@@ -0,0 +1,144 @@
+# Minimal native Query Regression fixture for the narrow direct-prom-rate sum fusion candidate.
+# This deterministic wave is not the original 127-slope counter/input archive.
+# Retain complete raw responses for parity auditing; passing thresholds only means
+# the configured latency guard did not trip, not that fusion or a speedup was proven.
+
+[case]
+name = "promql_series_rate_fusion"
+description = "PromQL rate-only grouped sum fusion regression fixture"
+
+[scenario]
+kind = "direct_readable_sst"
+seed = 25652
+
+[[scenario.tables]]
+database = "public"
+name = "promql_series_rate_fusion"
+engine = "mito"
+append_mode = true
+sst_format = "flat"
+primary_key = ["instance", "dc", "device"]
+time_index = "ts"
+
+[[scenario.tables.columns]]
+name = "instance"
+type = "STRING"
+semantic = "tag"
+distribution = { kind = "cardinality", values = 4096, prefix = "instance" }
+
+[[scenario.tables.columns]]
+name = "dc"
+type = "STRING"
+semantic = "tag"
+distribution = { kind = "cardinality", values = 16, prefix = "dc" }
+
+[[scenario.tables.columns]]
+name = "device"
+type = "STRING"
+semantic = "tag"
+distribution = { kind = "cardinality", values = 4, prefix = "device" }
+
+[[scenario.tables.columns]]
+name = "val"
+type = "DOUBLE"
+semantic = "field"
+distribution = { kind = "deterministic_wave", min = 0.0, max = 100.0 }
+
+[[scenario.tables.columns]]
+name = "ts"
+type = "TIMESTAMP(3)"
+semantic = "timestamp"
+
+[scenario.layout]
+regions = 1
+sst_count = 2
+rows_per_sst = 1048576
+row_group_size = 8192
+series_count = 4096
+start_unix_nanos = 1704067200000000000
+step_nanos = 15000000000
+time_range_layout = "non_overlapping_per_sst"
+series_layout = "timestamp_major"
+
+# 122 evaluations * 16 dc groups = 1,952 output rows. Each range evaluates
+# 4,096 series at 122 timestamps (499,712 evaluated series points). This range
+# crosses the first-SST boundary (1704071025); its initial 5m lookback starts
+# at 1704069600, ensuring both SSTs are in the requested time span.
+[[scenario.queries]]
+name = "grouped_rate_sum_range"
+kind = "tql"
+query = "TQL EVAL (1704069900, 1704071715, '15s') sum by (dc) (rate(promql_series_rate_fusion[5m]))"
+warmup = 3
+iterations = 20
+
+[scenario.queries.thresholds]
+max_candidate_latency_regression_pct = 10
+
+# Same complete response shape at the latest timestamp: 16 groups.
+[[scenario.queries]]
+name = "grouped_rate_sum_instant"
+kind = "tql"
+query = "TQL EVAL (1704071715, 1704071715, '15s') sum by (dc) (rate(promql_series_rate_fusion[5m]))"
+warmup = 3
+iterations = 9
+
+[scenario.queries.thresholds]
+max_candidate_latency_regression_pct = 10
+
+# Separate diagnostics are intentionally not included in timed samples.
+[[scenario.queries]]
+name = "analyze_grouped_rate_sum_range"
+kind = "tql"
+query = "TQL ANALYZE VERBOSE (1704069900, 1704071715, '15s') sum by (dc) (rate(promql_series_rate_fusion[5m]))"
+warmup = 0
+iterations = 1
+
+[[scenario.queries]]
+name = "analyze_grouped_rate_sum_instant"
+kind = "tql"
+query = "TQL ANALYZE VERBOSE (1704071715, 1704071715, '15s') sum by (dc) (rate(promql_series_rate_fusion[5m]))"
+warmup = 0
+iterations = 1
+
+# Wider/non-rate path: does not match the direct rate-only fusion candidate.
+[[scenario.queries]]
+name = "grouped_sum_over_time_control"
+kind = "tql"
+query = "TQL EVAL (1704069900, 1704071715, '15s') sum by (dc) (sum_over_time(promql_series_rate_fusion[5m]))"
+warmup = 3
+iterations = 9
+
+[scenario.queries.thresholds]
+max_candidate_latency_regression_pct = 10
+
+# MIN is a distinct aggregation operator, so it must not match the SUM fusion
+# candidate. It retains the same rate-window work and compact grouped response.
+[[scenario.queries]]
+name = "grouped_rate_min_control"
+kind = "tql"
+query = "TQL EVAL (1704069900, 1704071715, '15s') min by (dc) (rate(promql_series_rate_fusion[5m]))"
+warmup = 3
+iterations = 9
+
+[scenario.queries.thresholds]
+max_candidate_latency_regression_pct = 10
+
+# Complete-table materialization audit: 16 rows, each dc has 131072 rows and
+# 256 instances, with timestamps spanning the entire two-SST fixture.
+[[scenario.queries]]
+name = "validate_materialized_data"
+kind = "sql"
+query = "SELECT dc, COUNT(*) AS row_count, COUNT(DISTINCT instance) AS series_count, MIN(ts) AS min_ts, MAX(ts) AS max_ts FROM promql_series_rate_fusion GROUP BY dc ORDER BY dc"
+warmup = 0
+iterations = 1
+
+# Offset gate control, if accepted by this pinned parser; an offset is not fused.
+[[scenario.queries]]
+name = "grouped_rate_sum_offset_control"
+kind = "tql"
+query = "TQL EVAL (1704069900, 1704071715, '15s') sum by (dc) (rate(promql_series_rate_fusion[5m] offset 15s))"
+warmup = 3
+iterations = 9
+
+[scenario.queries.thresholds]
+max_candidate_latency_regression_pct = 10