diff --git a/.github/workflows/deploy-telemetry.yml b/.github/workflows/deploy-telemetry.yml
index 3d71a50..bef536e 100644
--- a/.github/workflows/deploy-telemetry.yml
+++ b/.github/workflows/deploy-telemetry.yml
@@ -65,6 +65,28 @@ jobs:
               --env-file deploy/telemetry/.env \
               -f deploy/telemetry/docker-compose.yml \
               restart caddy
+            public_host="$(sed -n 's/^TELEMETRY_PUBLIC_HOST=//p' deploy/telemetry/.env | tail -n 1)"
+            test -n "$public_host"
+            printf '%s' "$public_host" | grep -Eq '^[A-Za-z0-9]([A-Za-z0-9.-]*[A-Za-z0-9])?$'
+            for attempt in $(seq 1 30); do
+              if curl -fsS --connect-timeout 5 --max-time 15 "https://$public_host/readyz" >/dev/null; then
+                break
+              fi
+              test "$attempt" -lt 30
+              sleep 2
+            done
+            for user_agent in ti/deploy-smoke tdc/deploy-smoke; do
+              response="$(curl -sS --connect-timeout 5 --max-time 15 \
+                -H 'Content-Type: application/json' \
+                -H "User-Agent: $user_agent" \
+                --data '{}' \
+                -w '\n%{http_code}' \
+                "https://$public_host/v1/telemetry/batch")"
+              status="${response##*$'\n'}"
+              body="${response%$'\n'*}"
+              test "$status" = "400"
+              printf '%s' "$body" | grep -F '"message":"schema validation failed"' >/dev/null
+            done
             docker compose \
               --env-file deploy/telemetry/.env \
               -f deploy/telemetry/docker-compose.yml \
diff --git a/README.md b/README.md
index f0474a7..07079fa 100644
--- a/README.md
+++ b/README.md
@@ -141,6 +141,8 @@ Use `TI_LOGGING=off` to disable logging for one process. Accepted values are `on
 
 Release builds collect minimal command usage and reliability telemetry through the ti-owned ingestion service. Events contain canonical command and explicitly supplied flag names, stable exit and error codes, duration, region, ti version, OS, architecture, install source, and a random installation ID. They never contain flag values, credentials, tokens, SQL text, paths, file contents, command output, API payloads, profile names, or cloud resource IDs.
 
+During the v0.2 migration window, the ingestion backend accepts both current `ti/<version>` and legacy `tdc/<version>` User-Agent values. All other User-Agent prefixes are rejected before payload validation.
+
 Telemetry is disabled by default for development builds and recognized CI environments. To disable it persistently for release builds, create or edit `~/.ti/.preferences`:
 
 ```toml
diff --git a/docs/telemetry-backend-design.md b/docs/telemetry-backend-design.md
index 2571528..0e122e3 100644
--- a/docs/telemetry-backend-design.md
+++ b/docs/telemetry-backend-design.md
@@ -94,6 +94,8 @@ Content-Type: application/json
 User-Agent: ti/<version>
 ```
 
+During the v0.2 migration window, the backend also accepts the legacy `User-Agent: tdc/<version>` value. No other User-Agent prefix is accepted. Deployment smoke tests must verify both accepted prefixes against the public endpoint; a schema-invalid probe must reach payload validation instead of failing header validation.
+
 Request limits:
 
 - Body size: default 64 KiB.
diff --git a/internal/telemetrybackend/server.go b/internal/telemetrybackend/server.go
index c88047b..895a617 100644
--- a/internal/telemetrybackend/server.go
+++ b/internal/telemetrybackend/server.go
@@ -263,10 +263,16 @@ func validContentType(raw string) bool {
 }
 
 func validUserAgent(value string) bool {
-	return strings.HasPrefix(value, "ti/") &&
-		len(value) > len("ti/") &&
-		len(value) <= 128 &&
-		!strings.ContainsAny(value, "\r\n\t ")
+	prefixLength := 0
+	switch {
+	case strings.HasPrefix(value, "ti/"):
+		prefixLength = len("ti/")
+	case strings.HasPrefix(value, "tdc/"):
+		prefixLength = len("tdc/")
+	default:
+		return false
+	}
+	return len(value) > prefixLength && len(value) <= 128 && !strings.ContainsAny(value, "\r\n\t ")
 }
 
 var errBodyTooLarge = errors.New("request body too large")
diff --git a/internal/telemetrybackend/server_test.go b/internal/telemetrybackend/server_test.go
index 900075b..d5ee231 100644
--- a/internal/telemetrybackend/server_test.go
+++ b/internal/telemetrybackend/server_test.go
@@ -37,6 +37,32 @@ func TestServerAcceptsValidBatchWith202BeforeFlush(t *testing.T) {
 	}
 }
 
+func TestServerAcceptsCurrentAndLegacyCLIUserAgents(t *testing.T) {
+	for _, userAgent := range []string{"ti/0.2.3", "tdc/0.1.7"} {
+		t.Run(userAgent, func(t *testing.T) {
+			cfg := testConfig()
+			batcher := NewBatcher(cfg, nil, discardLogger(), nil)
+			server := NewServer(cfg, batcher, readinessStub{}, readinessStub{}, discardLogger(), nil)
+			request := newBatchRequest(validRequestBody())
+			request.Header.Set("User-Agent", userAgent)
+			response := httptest.NewRecorder()
+			server.Handler().ServeHTTP(response, request)
+			if response.Code != http.StatusAccepted {
+				t.Fatalf("status = %d, want %d; body=%s", response.Code, http.StatusAccepted, response.Body.String())
+			}
+		})
+	}
+}
+
+func TestValidUserAgentRejectsMalformedOrUntrustedValues(t *testing.T) {
+	tooLong := "ti/" + strings.Repeat("v", 126)
+	for _, userAgent := range []string{"", "ti/", "tdc/", "curl/8", "ti/0.2.3 debug", "tdc/0.1.7\n", tooLong} {
+		if validUserAgent(userAgent) {
+			t.Errorf("validUserAgent(%q) = true", userAgent)
+		}
+	}
+}
+
 func TestServerRejectsInvalidRequestsWithGenericErrors(t *testing.T) {
 	cfg := testConfig()
 	cfg.MaxBodyBytes = int64(len(validRequestBody()))