diff --git a/internal/proxy/iolog_test.go b/internal/proxy/iolog_test.go
index d91cc99..d6553b8 100644
--- a/internal/proxy/iolog_test.go
+++ b/internal/proxy/iolog_test.go
@@ -1,6 +1,7 @@
 package proxy
 
 import (
+	"bytes"
 	"context"
 	"io"
 	"net/http"
@@ -308,3 +309,86 @@ func TestIOLog_SinkReceivesRecordViaOnDone(t *testing.T) {
 		t.Fatalf("opted-in request must hand exactly 1 record to the sink, got %d", got)
 	}
 }
+
+// newIOLogServerWithLog is newIOLogServer but with a caller-supplied logger, so a
+// test can capture WARN output (the request-body-truncation observability line).
+func newIOLogServerWithLog(t *testing.T, upstream *url.URL, policy iolog.Policy, sink iolog.Sink, maxBody int, log *logging.Logger) *Server {
+	t.Helper()
+	s := &config.Settings{ListenAddr: ":0"}
+	resolver := registry.NewStatic(upstream)
+	return NewWithIOLog(s, log, resolver, &recordingEmitter{}, policy, sink, maxBody)
+}
+
+// TestIOLog_RequestTruncationLogged verifies Hugo's D1 decision: hard truncation
+// of the captured request body is fine, but it must be OBSERVABLE — a single WARN
+// line fires (with request_id and original→cap sizes) ONLY when the body exceeds
+// the cap, and stays silent for an under-cap body.
+func TestIOLog_RequestTruncationLogged(t *testing.T) {
+	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// Drain so the upstream still sees the full forwarded body.
+		_, _ = io.Copy(io.Discard, r.Body)
+		_, _ = io.WriteString(w, `{"ok":true,"model":"m"}`)
+	}))
+	defer backend.Close()
+	upstream, _ := url.Parse(backend.URL)
+
+	const bodyCap = 100
+
+	t.Run("over cap logs", func(t *testing.T) {
+		var buf bytes.Buffer
+		log := logging.New(logging.WARN)
+		log.Warn.SetOutput(&buf)
+
+		policy := &spyPolicy{decision: true}
+		sink := &recordingSink{}
+		srv := newIOLogServerWithLog(t, upstream, policy, sink, bodyCap, log)
+
+		big := strings.Repeat("A", 500)
+		rr := httptest.NewRecorder()
+		srv.Handler().ServeHTTP(rr, iologRequest(http.MethodPost, big))
+
+		if rr.Code != http.StatusOK {
+			t.Fatalf("status = %d, want 200", rr.Code)
+		}
+		// The record must mark the request body truncated...
+		recs := sink.all()
+		if len(recs) != 1 || !recs[0].RequestTruncated {
+			t.Fatalf("expected 1 record with RequestTruncated=true, got %+v", recs)
+		}
+		// ...and the WARN line must fire with request_id and original→cap sizes.
+		out := buf.String()
+		if !strings.Contains(out, "request body truncated") {
+			t.Fatalf("no truncation WARN logged; got %q", out)
+		}
+		if !strings.Contains(out, "request_id=req-iolog-1") {
+			t.Errorf("WARN missing request_id; got %q", out)
+		}
+		if !strings.Contains(out, "500 → 100 bytes") {
+			t.Errorf("WARN missing original→cap sizes (want \"500 → 100 bytes\"); got %q", out)
+		}
+	})
+
+	t.Run("under cap silent", func(t *testing.T) {
+		var buf bytes.Buffer
+		log := logging.New(logging.WARN)
+		log.Warn.SetOutput(&buf)
+
+		policy := &spyPolicy{decision: true}
+		sink := &recordingSink{}
+		srv := newIOLogServerWithLog(t, upstream, policy, sink, bodyCap, log)
+
+		rr := httptest.NewRecorder()
+		srv.Handler().ServeHTTP(rr, iologRequest(http.MethodPost, `{"model":"m"}`))
+
+		if rr.Code != http.StatusOK {
+			t.Fatalf("status = %d, want 200", rr.Code)
+		}
+		recs := sink.all()
+		if len(recs) != 1 || recs[0].RequestTruncated {
+			t.Fatalf("under-cap body must not be truncated; got %+v", recs)
+		}
+		if out := buf.String(); strings.Contains(out, "request body truncated") {
+			t.Errorf("under-cap body must NOT log truncation; got %q", out)
+		}
+	})
+}
diff --git a/internal/proxy/proxy.go b/internal/proxy/proxy.go
index 42ec17e..7c71c01 100644
--- a/internal/proxy/proxy.go
+++ b/internal/proxy/proxy.go
@@ -251,12 +251,20 @@ func (s *Server) handleProxy(w http.ResponseWriter, r *http.Request) {
 		// Cap the LOGGED request-body copy at the same bound as the response copy
 		// (s.ioMaxBodyLen) — an uncapped body flows into to_tsvector and fails the
 		// INSERT past ~1 MiB. The forwarded request keeps the full body.
-		reqBody, reqTruncated, err = captureRequestBody(r, s.ioMaxBodyLen)
+		var reqOrigLen int
+		reqBody, reqTruncated, reqOrigLen, err = captureRequestBody(r, s.ioMaxBodyLen)
 		if err != nil {
 			s.log.Error.Printf("capture request body: %v", err)
 			http.Error(w, "bad request body", http.StatusBadRequest)
 			return
 		}
+		// Hard truncation is intentional (an uncapped body fails the to_tsvector
+		// INSERT), but make it OBSERVABLE: an operator should be able to see that
+		// a captured body was cut, and by how much.
+		if reqTruncated {
+			s.log.Warn.Printf("iolog: request body truncated for capture request_id=%s (%d → %d bytes)",
+				requestID, reqOrigLen, s.ioMaxBodyLen)
+		}
 	}
 
 	// Force streaming usage so we never under-bill a streamed response.
diff --git a/internal/proxy/rewrite.go b/internal/proxy/rewrite.go
index 5f59985..c7e22ab 100644
--- a/internal/proxy/rewrite.go
+++ b/internal/proxy/rewrite.go
@@ -24,15 +24,17 @@ import (
 // the model sees — only the stored log copy. Truncation is at a rune boundary so
 // the stored TEXT is valid UTF-8. maxBodyBytes <= 0 means uncapped.
 //
-// A nil body yields ("", false) with no error.
-func captureRequestBody(r *http.Request, maxBodyBytes int) (body string, truncated bool, err error) {
+// A nil body yields ("", false, 0) with no error. origLen is the size of the
+// FULL body read off the wire (before capping), so a caller can log the
+// original-vs-cap sizes when truncated is true.
+func captureRequestBody(r *http.Request, maxBodyBytes int) (body string, truncated bool, origLen int, err error) {
 	if r.Body == nil {
-		return "", false, nil
+		return "", false, 0, nil
 	}
 	raw, err := io.ReadAll(r.Body)
 	_ = r.Body.Close()
 	if err != nil {
-		return "", false, err
+		return "", false, 0, err
 	}
 	// Restore the FULL body so forceIncludeUsage (and the upstream) read every
 	// byte — the cap only bounds the LOG copy, never the forwarded request.
@@ -41,7 +43,7 @@ func captureRequestBody(r *http.Request, maxBodyBytes int) (body string, truncat
 	r.Header.Set("Content-Length", strconv.Itoa(len(raw)))
 
 	logCopy, truncated := truncateAtRuneBoundary(raw, maxBodyBytes)
-	return string(logCopy), truncated, nil
+	return string(logCopy), truncated, len(raw), nil
 }
 
 // forceIncludeUsage rewrites a request body so that streamed responses carry a
diff --git a/internal/rating/store.go b/internal/rating/store.go
index 4395d30..275cc4d 100644
--- a/internal/rating/store.go
+++ b/internal/rating/store.go
@@ -325,7 +325,7 @@ priced AS (
           + cached_tokens     * cached_price
           + completion_tokens * completion_price
         )                                                AS cost,
-        COUNT(*)::int                                    AS event_count
+        COUNT(*)::bigint                                 AS event_count
     FROM resolved
     WHERE prompt_price IS NOT NULL          -- priced only
       AND auth_id  IS NOT NULL              -- attributable only
diff --git a/internal/rating/store_integration_test.go b/internal/rating/store_integration_test.go
index c799be4..8970ef3 100644
--- a/internal/rating/store_integration_test.go
+++ b/internal/rating/store_integration_test.go
@@ -96,7 +96,7 @@ CREATE TABLE rated_usage (
     completion_tokens      BIGINT NOT NULL,
     billable_prompt_tokens BIGINT NOT NULL,
     cost                   NUMERIC(20,9) NOT NULL,
-    event_count            INTEGER NOT NULL,
+    event_count            BIGINT NOT NULL,
     rated_at               TIMESTAMPTZ NOT NULL DEFAULT now(),
     CONSTRAINT rated_usage_auth_model_window_uq UNIQUE (auth_id, model_id, window_start)
 );`
@@ -472,6 +472,59 @@ func TestIntegration_RatingInstantIndexServesScan(t *testing.T) {
 	}
 }
 
+// TestIntegration_EventCountIsBigint pins D2: rated_usage.event_count must be a
+// BIGINT, so a rollup counting more than 2^31 events INSERTs and round-trips
+// instead of overflowing INTEGER. Asserts both the declared column type and an
+// actual > 2^31 value surviving INSERT + SELECT.
+func TestIntegration_EventCountIsBigint(t *testing.T) {
+	dsn := os.Getenv("PHOEBE_TEST_DATABASE_URL")
+	if dsn == "" {
+		t.Skip("PHOEBE_TEST_DATABASE_URL not set; skipping live-Postgres conformance")
+	}
+	db, err := sql.Open("pgx", dsn)
+	if err != nil {
+		t.Fatalf("open: %v", err)
+	}
+	defer db.Close()
+	db.SetMaxOpenConns(1) // SET/search_path must stick
+
+	const sch = "phoebe_rating_bigint_it"
+	exec(t, db, "DROP SCHEMA IF EXISTS "+sch+" CASCADE")
+	exec(t, db, "CREATE SCHEMA "+sch)
+	exec(t, db, "SET search_path TO "+sch)
+	defer func() { exec(t, db, "DROP SCHEMA IF EXISTS "+sch+" CASCADE") }()
+	exec(t, db, schemaDDL)
+
+	// The declared column type must be bigint, not integer.
+	var dataType string
+	if err := db.QueryRow(
+		`SELECT data_type FROM information_schema.columns
+		   WHERE table_schema = $1 AND table_name = 'rated_usage' AND column_name = 'event_count'`,
+		sch).Scan(&dataType); err != nil {
+		t.Fatalf("read event_count column type: %v", err)
+	}
+	if dataType != "bigint" {
+		t.Fatalf("rated_usage.event_count data_type = %q, want \"bigint\"", dataType)
+	}
+
+	// A value past INT32_MAX must INSERT and round-trip unharmed.
+	const bigCount int64 = 5_000_000_000 // > 2^31-1 (2_147_483_647)
+	exec(t, db, fmt.Sprintf(`INSERT INTO rated_usage
+		(id, auth_id, model_id, window_start, window_end,
+		 prompt_tokens, cached_tokens, completion_tokens, billable_prompt_tokens, cost, event_count)
+		VALUES ('bc1','a','b','2026-06-08T10:00:00Z','2026-06-08T11:00:00Z',
+		        0,0,0,0,0, %d)`, bigCount))
+
+	var got int64
+	if err := db.QueryRow(
+		`SELECT event_count FROM rated_usage WHERE id = 'bc1'`).Scan(&got); err != nil {
+		t.Fatalf("read back event_count: %v", err)
+	}
+	if got != bigCount {
+		t.Fatalf("event_count round-trip = %d, want %d", got, bigCount)
+	}
+}
+
 func exec(t *testing.T, db *sql.DB, q string) {
 	t.Helper()
 	if _, err := db.Exec(q); err != nil {
diff --git a/migrations/0002_rating.sql b/migrations/0002_rating.sql
index 26556a9..3fb9878 100644
--- a/migrations/0002_rating.sql
+++ b/migrations/0002_rating.sql
@@ -217,7 +217,9 @@ CREATE TABLE rated_usage (
 
     -- The money, as exact NUMERIC. Computed and summed in SQL (never in Go).
     cost                    NUMERIC(20, 9) NOT NULL,
-    event_count             INTEGER NOT NULL,
+    -- BIGINT, not INTEGER: a wide rollup window can count more than 2^31 events,
+    -- which the COUNT(*)::bigint cast in the rater already produces.
+    event_count             BIGINT NOT NULL,
 
     rated_at                TIMESTAMPTZ NOT NULL DEFAULT now(),
 
diff --git a/migrations/atlas/c2f1a3b4d5e6_add_rating.py b/migrations/atlas/c2f1a3b4d5e6_add_rating.py
index 00ca054..aa8b771 100644
--- a/migrations/atlas/c2f1a3b4d5e6_add_rating.py
+++ b/migrations/atlas/c2f1a3b4d5e6_add_rating.py
@@ -179,7 +179,10 @@ def upgrade():
         sa.Column("billable_prompt_tokens", sa.BigInteger(), nullable=False),
         # The money, exact NUMERIC, computed and summed in SQL.
         sa.Column("cost", MONEY, nullable=False),
-        sa.Column("event_count", sa.Integer(), nullable=False),
+        # BigInteger, not Integer: a wide rollup window can count more than
+        # 2^31 events (matches the COUNT(*)::bigint cast in the rater). No data
+        # migration is needed — rated_usage is empty pre-prod.
+        sa.Column("event_count", sa.BigInteger(), nullable=False),
         sa.Column(
             "rated_at",
             sa.DateTime(timezone=True),