diff --git a/internal/gateway/anthropic.go b/internal/gateway/anthropic.go
index dfcef5cd..074ecfa4 100644
--- a/internal/gateway/anthropic.go
+++ b/internal/gateway/anthropic.go
@@ -691,6 +691,12 @@ func (e *anthropicEncoder) event(ev Event) {
 	e.col.add(ev)
 }
 
+// keepalive is Anthropic's own: a ping event, which its SDKs skip and
+// Claude Code's stream watchdog counts.
+func (e *anthropicEncoder) keepalive() {
+	e.w.event("ping", map[string]any{"type": "ping"})
+}
+
 func (e *anthropicEncoder) finish() {
 	if !e.started {
 		e.start(Event{})
diff --git a/internal/gateway/chat.go b/internal/gateway/chat.go
index b45b5ae3..29e40cdf 100644
--- a/internal/gateway/chat.go
+++ b/internal/gateway/chat.go
@@ -807,6 +807,10 @@ func (e *chatEncoder) event(ev Event) {
 	e.col.add(ev)
 }
 
+// keepalive is an SSE comment, as OpenAI-compatible servers keep a Chat
+// Completions stream alive; its readers skip one.
+func (e *chatEncoder) keepalive() { e.w.comment("keepalive") }
+
 func (e *chatEncoder) finish() {
 	if !e.started {
 		e.start(Event{})
diff --git a/internal/gateway/claude_subscription.go b/internal/gateway/claude_subscription.go
index e94088c5..7834144b 100644
--- a/internal/gateway/claude_subscription.go
+++ b/internal/gateway/claude_subscription.go
@@ -1478,7 +1478,8 @@ func relay(w http.ResponseWriter, r *http.Request, from provider.Protocol, name
 			}
 			return writeError(w, from, code, name+": "+msg), msg
 		}
-		enc := encoder(from, newSSEWriter(w), req)
+		sw := newSSEWriter(w)
+		enc := encoder(from, sw, req)
 		var failed, said, stop string
 		see := func(ev Event) {
 			switch ev.Kind {
@@ -1497,9 +1498,12 @@ func relay(w http.ResponseWriter, r *http.Request, from provider.Protocol, name
 		for _, ev := range head {
 			see(ev)
 		}
-		for ev := range events {
+		// a client waiting on a reply that goes on is kept from its idle
+		// timeout while none of it comes (#436)
+		relayEvents(events, sw, enc, func(ev Event) bool {
 			see(ev)
-		}
+			return true
+		})
 		// before the reply's last event, which the agent may answer at once
 		ended(said, stop, failed == "" && r.Context().Err() == nil)
 		// an error event already ended the reply in the client's protocol
diff --git a/internal/gateway/gateway.go b/internal/gateway/gateway.go
index 54adfe46..ee29a914 100644
--- a/internal/gateway/gateway.go
+++ b/internal/gateway/gateway.go
@@ -2288,9 +2288,10 @@ func (s *Server) translate(w http.ResponseWriter, r *http.Request, p provider.Pr
 		return writeError(w, from, 502, msg), msg
 	}
 	if stream {
-		enc := encoder(from, newSSEWriter(w), request)
+		sw := newSSEWriter(w)
+		enc := encoder(from, sw, request)
 		var failed string
-		serr := readSSE(rd, func(_, data string) error {
+		serr := readSSEAlive(rd, func(_, data string) error {
 			return dec(data, func(ev Event) {
 				switch ev.Kind {
 				case KError:
@@ -2301,6 +2302,12 @@ func (s *Server) translate(w http.ResponseWriter, r *http.Request, p provider.Pr
 				}
 				enc.event(ev)
 			})
+		}, func() {
+			// the provider's keepalives aren't events to translate: while
+			// it is heard from, the client hears from magpie (#436)
+			if failed == "" && sw.quiet() >= keepaliveGap {
+				enc.keepalive()
+			}
 		})
 		if serr != nil && failed == "" {
 			// the upstream died mid-reply: say so in the client's own
@@ -2429,6 +2436,44 @@ func decoder(proto provider.Protocol) func(data string, emit func(Event)) error
 type streamEncoder interface {
 	event(Event)
 	finish()
+	// keepalive tells the client the reply goes on, as its protocol does
+	// with no answer to give: one its idle timeout counts (#436)
+	keepalive()
+}
+
+// keepaliveGap is how long a translated reply's client may hear nothing
+// while its provider is heard from (a keepalive, an event that has nothing
+// for the client) before it is sent a keepalive of its own.
+var keepaliveGap = time.Second
+
+// keepaliveEvery is how often a relayed reply that has gone quiet is kept
+// alive, and keepaliveLongest how long it is kept so with no event: a
+// reply stuck longer is left for the client's own idle timeout to end.
+var keepaliveEvery, keepaliveLongest = 15 * time.Second, 5 * time.Minute
+
+// relayEvents hands see each of events until they end or see says stop,
+// keeping the client of sw alive while none comes (keepaliveEvery, for up
+// to keepaliveLongest since the last).
+func relayEvents(events <-chan Event, sw *sseWriter, enc streamEncoder, see func(Event) bool) {
+	tick := time.NewTicker(keepaliveEvery)
+	defer tick.Stop()
+	last := time.Now()
+	for {
+		select {
+		case ev, ok := <-events:
+			if !ok {
+				return
+			}
+			last = time.Now()
+			if !see(ev) {
+				return
+			}
+		case <-tick.C:
+			if time.Since(last) < keepaliveLongest && sw.quiet() >= keepaliveEvery/2 {
+				enc.keepalive()
+			}
+		}
+	}
 }
 
 func encoder(proto provider.Protocol, w *sseWriter, r *Request) streamEncoder {
diff --git a/internal/gateway/gemini.go b/internal/gateway/gemini.go
index a8f4930b..0665f306 100644
--- a/internal/gateway/gemini.go
+++ b/internal/gateway/gemini.go
@@ -420,6 +420,11 @@ func (e *geminiEncoder) chunk(parts []map[string]any, finish string, usage map[s
 	e.w.event("", msg)
 }
 
+// keepalive sends nothing: Google's SDK takes a stream's "data: " lines
+// one after another from the front and gets stuck on anything else, a
+// comment too, and there is no event without content to send instead.
+func (e *geminiEncoder) keepalive() {}
+
 func (e *geminiEncoder) start(ev Event) {
 	if e.started {
 		return
diff --git a/internal/gateway/keepalive_test.go b/internal/gateway/keepalive_test.go
new file mode 100644
index 00000000..75c4a90f
--- /dev/null
+++ b/internal/gateway/keepalive_test.go
@@ -0,0 +1,245 @@
+package gateway
+
+import (
+	"bufio"
+	"context"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/yetone/magpie/internal/provider"
+)
+
+// keepFast makes the keepalives of a test's streams come at its pace.
+func keepFast(t *testing.T, gap, every, longest time.Duration) {
+	t.Helper()
+	g, e, l := keepaliveGap, keepaliveEvery, keepaliveLongest
+	keepaliveGap, keepaliveEvery, keepaliveLongest = gap, every, longest
+	t.Cleanup(func() { keepaliveGap, keepaliveEvery, keepaliveLongest = g, e, l })
+}
+
+// TestTranslatedStreamKeepsClientAlive: a provider that says "progress",
+// then only ": keepalive" every 20ms for half a second, then finishes,
+// translated for a client whose idle timeout is 150ms (#436, congee949's
+// repro). The client must hear something it counts all along: Codex's
+// timeout counts events, never a comment, so a Responses or Anthropic
+// client is kept alive with events, a Chat one with comments.
+func TestTranslatedStreamKeepsClientAlive(t *testing.T) {
+	keepFast(t, 10*time.Millisecond, keepaliveEvery, keepaliveLongest)
+	for _, c := range []struct {
+		name, path, body, done, ping string
+		upChat                       bool
+		comments                     bool // the client counts a comment as life
+	}{
+		{"chat_to_responses", "/v1/responses", `{"model":"fake/m1","stream":true,"input":"hi"}`,
+			`"type":"response.completed"`, `"type":"response.in_progress"`, true, false},
+		{"chat_to_anthropic", "/v1/messages", `{"model":"fake/m1","stream":true,"max_tokens":64,"messages":[{"role":"user","content":"hi"}]}`,
+			`"type":"message_stop"`, `"type":"ping"`, true, false},
+		{"responses_to_chat", "/v1/chat/completions", `{"model":"fake/m1","stream":true,"messages":[{"role":"user","content":"hi"}]}`,
+			`"finish_reason":"stop"`, ": keepalive", false, true},
+	} {
+		t.Run(c.name, func(t *testing.T) {
+			fresh(t)
+			var upPings atomic.Int32
+			up := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				io.Copy(io.Discard, r.Body)
+				w.Header().Set("Content-Type", "text/event-stream")
+				f := w.(http.Flusher)
+				if c.upChat {
+					io.WriteString(w, "data: "+`{"id":"c1","model":"m1","choices":[{"index":0,"delta":{"content":"progress"},"finish_reason":null}]}`+"\n\n")
+				} else {
+					io.WriteString(w, "event: response.created\ndata: "+`{"type":"response.created","response":{"id":"r1","model":"m1"}}`+"\n\n")
+					io.WriteString(w, "event: response.output_text.delta\ndata: "+`{"type":"response.output_text.delta","delta":"progress"}`+"\n\n")
+				}
+				f.Flush()
+				tick := time.NewTicker(20 * time.Millisecond)
+				defer tick.Stop()
+				end := time.NewTimer(500 * time.Millisecond)
+				defer end.Stop()
+				for {
+					select {
+					case <-r.Context().Done():
+						return
+					case <-tick.C:
+						if _, err := io.WriteString(w, ": keepalive\n\n"); err != nil {
+							return
+						}
+						upPings.Add(1)
+						f.Flush()
+					case <-end.C:
+						if c.upChat {
+							io.WriteString(w, "data: "+`{"id":"c1","model":"m1","choices":[{"index":0,"delta":{},"finish_reason":"stop"}]}`+"\n\ndata: [DONE]\n\n")
+						} else {
+							io.WriteString(w, "event: response.completed\ndata: "+`{"type":"response.completed","response":{"id":"r1","model":"m1","status":"completed","output":[]}}`+"\n\n")
+						}
+						f.Flush()
+						return
+					}
+				}
+			}))
+			defer up.Close()
+			p := provider.Provider{ID: "fake", Name: "Fake", Key: "fixture", Models: []string{"m1"}}
+			if c.upChat {
+				p.Chat = up.URL + "/v1"
+			} else {
+				p.Responses = up.URL + "/v1"
+			}
+			if err := provider.Save(p); err != nil {
+				t.Fatal(err)
+			}
+			server := httptest.NewServer(New().Handler())
+			defer server.Close()
+			ctx, cancel := context.WithCancel(context.Background())
+			defer cancel()
+			req, _ := http.NewRequestWithContext(ctx, "POST", server.URL+c.path, strings.NewReader(c.body))
+			req.Header.Set("Content-Type", "application/json")
+			res, err := http.DefaultClient.Do(req)
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer res.Body.Close()
+			lines := make(chan string, 128)
+			go func() {
+				defer close(lines)
+				sc := bufio.NewScanner(res.Body)
+				for sc.Scan() {
+					lines <- sc.Text()
+				}
+			}()
+			idle := time.NewTimer(150 * time.Millisecond)
+			defer idle.Stop()
+			timedOut, completed, pings := false, false, 0
+		read:
+			for {
+				select {
+				case line, ok := <-lines:
+					if !ok {
+						break read
+					}
+					if strings.Contains(line, c.ping) {
+						pings++
+					}
+					if strings.Contains(line, c.done) {
+						completed = true
+					}
+					// what the client's idle timeout counts
+					if strings.HasPrefix(line, "data:") || (c.comments && strings.HasPrefix(line, ":")) {
+						idle.Reset(150 * time.Millisecond)
+					}
+				case <-idle.C:
+					timedOut = true
+					break read
+				}
+			}
+			cancel()
+			t.Logf("upstream_keepalives=%d downstream_keepalives=%d idle_timeout=%v completed=%v", upPings.Load(), pings, timedOut, completed)
+			if timedOut || !completed || pings < 3 {
+				t.Fatal("the client wasn't kept alive while the provider was")
+			}
+		})
+	}
+}
+
+// TestTranslatedSilenceStillTimesOut: a provider that says nothing at all
+// isn't covered for; the client's idle timeout still ends the wait.
+func TestTranslatedSilenceStillTimesOut(t *testing.T) {
+	keepFast(t, 10*time.Millisecond, keepaliveEvery, keepaliveLongest)
+	fresh(t)
+	release := make(chan struct{})
+	up := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		io.Copy(io.Discard, r.Body)
+		w.Header().Set("Content-Type", "text/event-stream")
+		io.WriteString(w, "data: "+`{"id":"c1","model":"m1","choices":[{"index":0,"delta":{"content":"progress"},"finish_reason":null}]}`+"\n\n")
+		w.(http.Flusher).Flush()
+		select {
+		case <-r.Context().Done():
+		case <-release:
+		}
+	}))
+	defer up.Close()
+	defer close(release)
+	if err := provider.Save(provider.Provider{ID: "fake", Name: "Fake", Key: "fixture", Models: []string{"m1"}, Chat: up.URL + "/v1"}); err != nil {
+		t.Fatal(err)
+	}
+	server := httptest.NewServer(New().Handler())
+	defer server.Close()
+	ctx, cancel := context.WithTimeout(context.Background(), 400*time.Millisecond)
+	defer cancel()
+	req, _ := http.NewRequestWithContext(ctx, "POST", server.URL+"/v1/responses", strings.NewReader(`{"model":"fake/m1","stream":true,"input":"hi"}`))
+	res, err := http.DefaultClient.Do(req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer res.Body.Close()
+	b, _ := io.ReadAll(res.Body)
+	if n := strings.Count(string(b), `"type":"response.in_progress"`); n > 1 {
+		t.Fatalf("a silent provider was covered for: %d in_progress events\n%s", n, b)
+	}
+}
+
+// TestRelayKeepsClientAlive: a relayed reply (the Claude subscription's
+// bridge, Kiro, Cursor, …) that goes quiet keeps its client alive every
+// keepaliveEvery, but only for keepaliveLongest since its last event.
+func TestRelayKeepsClientAlive(t *testing.T) {
+	keepFast(t, keepaliveGap, 20*time.Millisecond, 200*time.Millisecond)
+	events := make(chan Event)
+	go func() {
+		events <- Event{Kind: KStart, MsgID: "m1"}
+		events <- Event{Kind: KText, Text: "progress"}
+		time.Sleep(150 * time.Millisecond) // kept alive
+		events <- Event{Kind: KText, Text: " more"}
+		time.Sleep(600 * time.Millisecond) // kept alive for 200ms only
+		events <- Event{Kind: KStop, Stop: "end_turn"}
+		close(events)
+	}()
+	rec := httptest.NewRecorder()
+	req := &Request{Model: "m1", Stream: true}
+	r := httptest.NewRequest("POST", "/v1/messages", nil)
+	code, failed := relay(rec, r, provider.Anthropic, "Bridge", req, events, &Usage{}, func() {}, func(string, string, bool) {})
+	if code != 200 || failed != "" {
+		t.Fatalf("relay: %d %q", code, failed)
+	}
+	body := rec.Body.String()
+	parts := strings.SplitN(body, "more", 2)
+	if len(parts) != 2 || !strings.Contains(body, "message_stop") {
+		t.Fatalf("reply incomplete:\n%s", body)
+	}
+	before, after := strings.Count(parts[0], `"type":"ping"`), strings.Count(parts[1], `"type":"ping"`)
+	t.Logf("pings in a 150ms gap: %d, in a 600ms gap (200ms kept): %d", before, after)
+	if before < 3 {
+		t.Fatalf("a quiet reply wasn't kept alive: %d pings in 150ms", before)
+	}
+	if after < 3 || after > 12 {
+		t.Fatalf("a reply quiet past keepaliveLongest was kept alive on: %d pings", after)
+	}
+}
+
+// TestTraceKeepsInflight: a request still going stays in the trace while
+// more than traceKeep come and finish after it (#436).
+func TestTraceKeepsInflight(t *testing.T) {
+	s := New()
+	pending := s.trace.begin(Route{Model: "pending", Time: time.Now()})
+	for i := 0; i < traceKeep+1; i++ {
+		r := s.trace.begin(Route{Model: "later", Time: time.Now()})
+		s.trace.update(r, func(r *Route) { r.Done, r.Status = true, 200 })
+	}
+	state := s.Trace(context.Background(), 0, 0)
+	found := false
+	for _, r := range state.Routes {
+		found = found || r.ID == pending.ID
+	}
+	if !found || len(state.Routes) != traceKeep {
+		t.Fatalf("pending visible %v, %d routes kept", found, len(state.Routes))
+	}
+	// more going than twice traceKeep: the oldest go after all
+	for i := 0; i < 2*traceKeep; i++ {
+		s.trace.begin(Route{Model: "going", Time: time.Now()})
+	}
+	if n := len(s.Trace(context.Background(), 0, 0).Routes); n != 2*traceKeep {
+		t.Fatalf("%d routes kept, want %d", n, 2*traceKeep)
+	}
+}
diff --git a/internal/gateway/qoder.go b/internal/gateway/qoder.go
index 1e9f3f85..9ef2b7cd 100644
--- a/internal/gateway/qoder.go
+++ b/internal/gateway/qoder.go
@@ -120,22 +120,28 @@ func relayStatus(w http.ResponseWriter, from provider.Protocol, name string, req
 		if len(head) == 0 || head[len(head)-1].Kind == KStart || head[len(head)-1].Kind == KUsage {
 			return fail(Event{Text: name + " ended without an answer"})
 		}
-		enc := encoder(from, newSSEWriter(w), req)
+		sw := newSSEWriter(w)
+		enc := encoder(from, sw, req)
+		var failed string
 		see := func(ev Event) bool {
 			if ev.Kind == KStart || ev.Kind == KUsage {
 				usage.add(ev.Usage)
 			}
 			enc.event(ev)
-			return ev.Kind != KError
+			if ev.Kind == KError {
+				failed = ev.Text
+				return false
+			}
+			return true
 		}
 		for _, ev := range head {
 			see(ev)
 		}
-		for ev := range events {
-			if !see(ev) {
-				abort()
-				return 200, ev.Text
-			}
+		// kept from the client's idle timeout while none comes (#436)
+		relayEvents(events, sw, enc, see)
+		if failed != "" {
+			abort()
+			return 200, failed
 		}
 		enc.finish()
 		return 200, ""
diff --git a/internal/gateway/responses.go b/internal/gateway/responses.go
index 687ec7e0..ee3a20a6 100644
--- a/internal/gateway/responses.go
+++ b/internal/gateway/responses.go
@@ -827,6 +827,16 @@ func (e *responsesEncoder) event(ev Event) {
 	e.col.add(ev)
 }
 
+// keepalive is response.in_progress again: Codex's idle timeout counts
+// events only, an SSE comment never reaching it, and skips this one.
+func (e *responsesEncoder) keepalive() {
+	if !e.started {
+		e.start(Event{}) // response.created and response.in_progress
+		return
+	}
+	e.send("response.in_progress", map[string]any{"response": e.response("in_progress", nil)})
+}
+
 func (e *responsesEncoder) finish() {
 	if !e.started {
 		e.start(Event{})
diff --git a/internal/gateway/sse.go b/internal/gateway/sse.go
index 892e5bd9..442f1062 100644
--- a/internal/gateway/sse.go
+++ b/internal/gateway/sse.go
@@ -7,11 +7,19 @@ import (
 	"io"
 	"net/http"
 	"strings"
+	"time"
 )
 
 // readSSE walks a server-sent event stream, calling fn with each event's
 // name and data. Data lines of one event are joined with newlines.
 func readSSE(r io.Reader, fn func(event, data string) error) error {
+	return readSSEAlive(r, fn, nil)
+}
+
+// readSSEAlive is readSSE that also calls alive, when not nil, after each
+// event and each comment: every sign that the stream is alive, a
+// keepalive (": keepalive") as much as an answer.
+func readSSEAlive(r io.Reader, fn func(event, data string) error, alive func()) error {
 	sc := bufio.NewScanner(r)
 	sc.Buffer(make([]byte, 0, 64<<10), 32<<20)
 	var event string
@@ -23,6 +31,9 @@ func readSSE(r io.Reader, fn func(event, data string) error) error {
 		}
 		err := fn(event, strings.Join(data, "\n"))
 		event, data = "", nil
+		if err == nil && alive != nil {
+			alive()
+		}
 		return err
 	}
 	for sc.Scan() {
@@ -33,6 +44,9 @@ func readSSE(r io.Reader, fn func(event, data string) error) error {
 				return err
 			}
 		case strings.HasPrefix(line, ":"):
+			if alive != nil {
+				alive()
+			}
 		case strings.HasPrefix(line, "event:"):
 			event = strings.TrimSpace(line[6:])
 		case strings.HasPrefix(line, "data:"):
@@ -50,6 +64,7 @@ type sseWriter struct {
 	w     http.ResponseWriter
 	f     http.Flusher
 	begun bool
+	wrote time.Time // when the client was last written to
 }
 
 func newSSEWriter(w http.ResponseWriter) *sseWriter {
@@ -69,6 +84,7 @@ func (s *sseWriter) begin() {
 	h.Set("X-Accel-Buffering", "no")
 	s.w.WriteHeader(http.StatusOK)
 	s.flush()
+	s.wrote = time.Now()
 }
 
 func (s *sseWriter) flush() {
@@ -77,6 +93,24 @@ func (s *sseWriter) flush() {
 	}
 }
 
+// quiet is how long the client has had nothing from s; a stream not yet
+// begun has been quiet for ever.
+func (s *sseWriter) quiet() time.Duration {
+	if !s.begun {
+		return 1<<63 - 1
+	}
+	return time.Since(s.wrote)
+}
+
+// comment writes an SSE comment, which every event stream reader skips:
+// no event, only the news that the stream is alive.
+func (s *sseWriter) comment(text string) {
+	s.begin()
+	io.WriteString(s.w, ": "+text+"\n\n")
+	s.flush()
+	s.wrote = time.Now()
+}
+
 // event writes one event; a JSON-marshallable value or a raw string.
 func (s *sseWriter) event(name string, v any) {
 	s.begin()
@@ -101,4 +135,5 @@ func (s *sseWriter) event(name string, v any) {
 	b.WriteString("\n\n")
 	s.w.Write(b.Bytes())
 	s.flush()
+	s.wrote = time.Now()
 }
diff --git a/internal/gateway/trace.go b/internal/gateway/trace.go
index 413ceb4c..42ea6c1a 100644
--- a/internal/gateway/trace.go
+++ b/internal/gateway/trace.go
@@ -10,6 +10,7 @@ package gateway
 
 import (
 	"context"
+	"slices"
 	"strings"
 	"sync"
 	"time"
@@ -299,14 +300,29 @@ func (t *trace) begin(r Route) *Route {
 	}
 	rp := &r
 	t.routes = append(t.routes, rp)
-	if len(t.routes) > traceKeep {
-		t.routes = t.routes[len(t.routes)-traceKeep:]
-	}
+	t.trim()
 	t.changed()
 	rp.Seq = t.seq
 	return rp
 }
 
+// trim keeps traceKeep routes, the oldest finished ones going first: a
+// request still going isn't dropped for those that came after it (#436),
+// as the history has only finished ones, unless more than twice traceKeep
+// are going at once.
+func (t *trace) trim() {
+	for len(t.routes) > traceKeep {
+		i := slices.IndexFunc(t.routes, func(r *Route) bool { return r.Done })
+		if i < 0 {
+			if len(t.routes) <= 2*traceKeep {
+				return
+			}
+			i = 0
+		}
+		t.routes = slices.Delete(t.routes, i, i+1)
+	}
+}
+
 // update changes a route under the lock.
 func (t *trace) update(r *Route, f func(r *Route)) {
 	if r == nil {