diff --git a/include/PgSQLErrorClassifier.h b/include/PgSQLErrorClassifier.h
new file mode 100644
index 000000000..471ddce40
--- /dev/null
+++ b/include/PgSQLErrorClassifier.h
@@ -0,0 +1,58 @@
+/**
+ * @file PgSQLErrorClassifier.h
+ * @brief Pure PgSQL error classification for retry decisions.
+ *
+ * Classifies PostgreSQL SQLSTATE error codes by class to determine
+ * if a query error is retryable or fatal.
+ *
+ * @see Phase 3.10 (GitHub issue #5498)
+ */
+
+#ifndef PGSQL_ERROR_CLASSIFIER_H
+#define PGSQL_ERROR_CLASSIFIER_H
+
+/**
+ * @brief Action to take after a PgSQL backend error.
+ */
+enum PgSQLErrorAction {
+	PGSQL_ERROR_REPORT_TO_CLIENT,  ///< Send error to client, no retry.
+	PGSQL_ERROR_RETRY,             ///< Retryable error (connection/server).
+	PGSQL_ERROR_FATAL              ///< Fatal server state (shutdown/crash).
+};
+
+/**
+ * @brief Classify a PgSQL SQLSTATE error code for retry eligibility.
+ *
+ * SQLSTATE classes (first 2 chars):
+ * - "08" (connection exception): retryable
+ * - "40" (transaction rollback, including serialization failure): retryable
+ * - "53" (insufficient resources, e.g. too_many_connections): retryable
+ * - "57" (operator intervention, e.g. admin_shutdown, crash_shutdown): fatal
+ *        Exception: "57014" (query_canceled) is non-fatal
+ * - "58" (system error, e.g. I/O error): fatal
+ * - All others (syntax, constraint, etc.): report to client
+ *
+ * @param sqlstate  5-character SQLSTATE string (e.g., "08006", "42P01").
+ * @return PgSQLErrorAction indicating what to do.
+ */
+PgSQLErrorAction classify_pgsql_error(const char *sqlstate);
+
+/**
+ * @brief Check if a PgSQL error is retryable given session conditions.
+ *
+ * Even if the error class is retryable, retry is blocked when:
+ * - In an active transaction (PgSQL transactions are atomic)
+ * - No retries remaining
+ *
+ * @param action              Result of classify_pgsql_error().
+ * @param retries_remaining   Number of retries left.
+ * @param in_transaction      Whether a transaction is in progress.
+ * @return true if the error can be retried.
+ */
+bool pgsql_can_retry_error(
+	PgSQLErrorAction action,
+	int retries_remaining,
+	bool in_transaction
+);
+
+#endif // PGSQL_ERROR_CLASSIFIER_H
diff --git a/lib/Makefile b/lib/Makefile
index 2d9ecc0d6..b00537d1c 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -109,6 +109,7 @@ _OBJ_CXX := ProxySQL_GloVars.oo network.oo debug.oo configfile.oo Query_Cache.oo
 	ServerSelection.oo \
 	TransactionState.oo \
 	HostgroupRouting.oo \
+	PgSQLErrorClassifier.oo \
 	PgSQLMonitorDecision.oo \
 	MySQLErrorClassifier.oo \
 	BackendSyncDecision.oo \
diff --git a/lib/PgSQLErrorClassifier.cpp b/lib/PgSQLErrorClassifier.cpp
new file mode 100644
index 000000000..cd48afcce
--- /dev/null
+++ b/lib/PgSQLErrorClassifier.cpp
@@ -0,0 +1,60 @@
+/**
+ * @file PgSQLErrorClassifier.cpp
+ * @brief Implementation of PgSQL error classification.
+ *
+ * @see PgSQLErrorClassifier.h
+ * @see Phase 3.10 (GitHub issue #5498)
+ */
+
+#include "PgSQLErrorClassifier.h"
+#include <cstring>
+
+PgSQLErrorAction classify_pgsql_error(const char *sqlstate) {
+	if (sqlstate == nullptr || strlen(sqlstate) < 2) {
+		return PGSQL_ERROR_REPORT_TO_CLIENT;
+	}
+
+	// Classify by SQLSTATE class (first 2 characters)
+	char cls[3] = {sqlstate[0], sqlstate[1], '\0'};
+
+	// Connection exceptions — retryable
+	if (strcmp(cls, "08") == 0) return PGSQL_ERROR_RETRY;
+
+	// Transaction rollback (serialization failure, deadlock) — retryable
+	if (strcmp(cls, "40") == 0) return PGSQL_ERROR_RETRY;
+
+	// Insufficient resources (too many connections) — retryable
+	if (strcmp(cls, "53") == 0) return PGSQL_ERROR_RETRY;
+
+	// Operator intervention — mostly fatal, except query_canceled
+	if (strcmp(cls, "57") == 0) {
+		// 57014 = query_canceled — not fatal, report to client
+		if (strlen(sqlstate) >= 5 && strncmp(sqlstate, "57014", 5) == 0) {
+			return PGSQL_ERROR_REPORT_TO_CLIENT;
+		}
+		return PGSQL_ERROR_FATAL;  // admin_shutdown, crash_shutdown, etc.
+	}
+
+	// System error (I/O error) — fatal
+	if (strcmp(cls, "58") == 0) return PGSQL_ERROR_FATAL;
+
+	// Everything else (syntax, constraints, data, etc.) — report to client
+	return PGSQL_ERROR_REPORT_TO_CLIENT;
+}
+
+bool pgsql_can_retry_error(
+	PgSQLErrorAction action,
+	int retries_remaining,
+	bool in_transaction)
+{
+	if (action != PGSQL_ERROR_RETRY) {
+		return false;
+	}
+	if (retries_remaining <= 0) {
+		return false;
+	}
+	if (in_transaction) {
+		return false;  // PgSQL transactions are atomic, can't retry mid-txn
+	}
+	return true;
+}
diff --git a/test/tap/tests/unit/Makefile b/test/tap/tests/unit/Makefile
index 0d9e39853..17cf47e0c 100644
--- a/test/tap/tests/unit/Makefile
+++ b/test/tap/tests/unit/Makefile
@@ -237,6 +237,7 @@ UNIT_TESTS := smoke_test-t query_cache_unit-t query_processor_unit-t \
 	server_selection_unit-t
   hostgroup_routing_unit-t \
 	transaction_state_unit-t \
+	pgsql_error_classifier_unit-t \
 	pgsql_monitor_unit-t \
 	mysql_error_classifier_unit-t \
 	backend_sync_unit-t
diff --git a/test/tap/tests/unit/pgsql_error_classifier_unit-t.cpp b/test/tap/tests/unit/pgsql_error_classifier_unit-t.cpp
new file mode 100644
index 000000000..396492415
--- /dev/null
+++ b/test/tap/tests/unit/pgsql_error_classifier_unit-t.cpp
@@ -0,0 +1,102 @@
+/**
+ * @file pgsql_error_classifier_unit-t.cpp
+ * @brief Unit tests for PgSQL error classification.
+ *
+ * @see Phase 3.10 (GitHub issue #5498)
+ */
+
+#include "tap.h"
+#include "test_globals.h"
+#include "test_init.h"
+#include "proxysql.h"
+#include "PgSQLErrorClassifier.h"
+
+static void test_connection_errors() {
+	ok(classify_pgsql_error("08000") == PGSQL_ERROR_RETRY,
+		"08000 (connection exception): retryable");
+	ok(classify_pgsql_error("08003") == PGSQL_ERROR_RETRY,
+		"08003 (connection does not exist): retryable");
+	ok(classify_pgsql_error("08006") == PGSQL_ERROR_RETRY,
+		"08006 (connection failure): retryable");
+}
+
+static void test_transaction_errors() {
+	ok(classify_pgsql_error("40001") == PGSQL_ERROR_RETRY,
+		"40001 (serialization failure): retryable");
+	ok(classify_pgsql_error("40P01") == PGSQL_ERROR_RETRY,
+		"40P01 (deadlock detected): retryable");
+}
+
+static void test_resource_errors() {
+	ok(classify_pgsql_error("53000") == PGSQL_ERROR_RETRY,
+		"53000 (insufficient resources): retryable");
+	ok(classify_pgsql_error("53300") == PGSQL_ERROR_RETRY,
+		"53300 (too many connections): retryable");
+}
+
+static void test_fatal_errors() {
+	ok(classify_pgsql_error("57000") == PGSQL_ERROR_FATAL,
+		"57000 (operator intervention): fatal");
+	ok(classify_pgsql_error("57P01") == PGSQL_ERROR_FATAL,
+		"57P01 (admin shutdown): fatal");
+	ok(classify_pgsql_error("57P02") == PGSQL_ERROR_FATAL,
+		"57P02 (crash shutdown): fatal");
+	ok(classify_pgsql_error("58000") == PGSQL_ERROR_FATAL,
+		"58000 (system error): fatal");
+	// 57014 is an exception — query_canceled is NOT fatal
+	ok(classify_pgsql_error("57014") == PGSQL_ERROR_REPORT_TO_CLIENT,
+		"57014 (query canceled): not fatal, report to client");
+}
+
+static void test_non_retryable_errors() {
+	ok(classify_pgsql_error("42601") == PGSQL_ERROR_REPORT_TO_CLIENT,
+		"42601 (syntax error): report");
+	ok(classify_pgsql_error("42P01") == PGSQL_ERROR_REPORT_TO_CLIENT,
+		"42P01 (undefined table): report");
+	ok(classify_pgsql_error("23505") == PGSQL_ERROR_REPORT_TO_CLIENT,
+		"23505 (unique violation): report");
+	ok(classify_pgsql_error("23503") == PGSQL_ERROR_REPORT_TO_CLIENT,
+		"23503 (foreign key violation): report");
+	ok(classify_pgsql_error("22001") == PGSQL_ERROR_REPORT_TO_CLIENT,
+		"22001 (string data right truncation): report");
+}
+
+static void test_edge_cases() {
+	ok(classify_pgsql_error(nullptr) == PGSQL_ERROR_REPORT_TO_CLIENT,
+		"null sqlstate: report");
+	ok(classify_pgsql_error("") == PGSQL_ERROR_REPORT_TO_CLIENT,
+		"empty sqlstate: report");
+	ok(classify_pgsql_error("0") == PGSQL_ERROR_REPORT_TO_CLIENT,
+		"single char sqlstate: report");
+}
+
+static void test_retry_conditions() {
+	ok(pgsql_can_retry_error(PGSQL_ERROR_RETRY, 3, false) == true,
+		"can retry: retryable + retries left + no txn");
+	ok(pgsql_can_retry_error(PGSQL_ERROR_RETRY, 0, false) == false,
+		"no retry: no retries left");
+	ok(pgsql_can_retry_error(PGSQL_ERROR_RETRY, 3, true) == false,
+		"no retry: in transaction");
+	ok(pgsql_can_retry_error(PGSQL_ERROR_REPORT_TO_CLIENT, 3, false) == false,
+		"no retry: non-retryable error");
+	ok(pgsql_can_retry_error(PGSQL_ERROR_FATAL, 3, false) == false,
+		"no retry: fatal error");
+}
+
+int main() {
+	plan(26);
+	int rc = test_init_minimal();
+	ok(rc == 0, "test_init_minimal() succeeds");
+
+	test_connection_errors();    // 3
+	test_transaction_errors();   // 2
+	test_resource_errors();      // 2
+	test_fatal_errors();         // 4
+	test_non_retryable_errors(); // 5
+	test_edge_cases();           // 3
+	test_retry_conditions();     // 5
+	// Total: 1+3+2+2+5+5+3+5 = 26
+
+	test_cleanup_minimal();
+	return exit_status();
+}