diff --git a/tee_gateway/__main__.py b/tee_gateway/__main__.py
index 3b317db..8b882f3 100644
--- a/tee_gateway/__main__.py
+++ b/tee_gateway/__main__.py
@@ -51,6 +51,11 @@
     COMPLETIONS_OPG_SESSION_MAX_SPEND,
     FACILITATOR_URL,
     OHTTP_OPG_SESSION_MAX_SPEND,
+    SETTLEMENT_POLL_INTERVAL_SECONDS,
+    SETTLEMENT_POLL_TIMEOUT_SECONDS,
+    UPTO_SESSION_IDLE_TIMEOUT_SECONDS,
+    UPTO_SESSION_MAX_TIMEOUT_SECONDS,
+    UPTO_SETTLEMENT_SAFETY_MARGIN_SECONDS,
 )
 
 # ---------------------------------------------------------------------------
@@ -267,7 +272,17 @@ def _init_payment_middleware(facilitator_url: str) -> None:
     Called once from set_provider_keys() after the facilitator URL is known.
     Swaps application.wsgi_app so all subsequent requests flow through it.
     """
-    facilitator = HTTPFacilitatorClientSync(FacilitatorConfig(url=facilitator_url))
+    # wait_for_settlement: the facilitator settles asynchronously (202 + job id).
+    # The reaper must confirm the on-chain result before marking a session settled,
+    # otherwise an expired/reverted settlement is silently dropped.
+    facilitator = HTTPFacilitatorClientSync(
+        FacilitatorConfig(
+            url=facilitator_url,
+            wait_for_settlement=True,
+            settlement_poll_interval=SETTLEMENT_POLL_INTERVAL_SECONDS,
+            settlement_poll_timeout=SETTLEMENT_POLL_TIMEOUT_SECONDS,
+        )
+    )
     server = x402ResourceServerSync(facilitator)  # type: ignore[arg-type]
     store = SessionStore()
 
@@ -290,6 +305,7 @@ def _init_payment_middleware(facilitator_url: str) -> None:
                         },
                     ),
                     network=BASE_MAINNET_NETWORK,
+                    max_timeout_seconds=UPTO_SESSION_MAX_TIMEOUT_SECONDS,
                 ),
             ],
             extensions={
@@ -313,6 +329,7 @@ def _init_payment_middleware(facilitator_url: str) -> None:
                         },
                     ),
                     network=BASE_MAINNET_NETWORK,
+                    max_timeout_seconds=UPTO_SESSION_MAX_TIMEOUT_SECONDS,
                 ),
             ],
             extensions={
@@ -336,6 +353,7 @@ def _init_payment_middleware(facilitator_url: str) -> None:
                         },
                     ),
                     network=BASE_MAINNET_NETWORK,
+                    max_timeout_seconds=UPTO_SESSION_MAX_TIMEOUT_SECONDS,
                 ),
             ],
             extensions={
@@ -358,7 +376,8 @@ def _init_payment_middleware(facilitator_url: str) -> None:
         server=server,
         session_store=store,
         cost_per_request=100000000000000,  # static precheck/fallback estimate
-        session_idle_timeout=100,
+        session_idle_timeout=UPTO_SESSION_IDLE_TIMEOUT_SECONDS,
+        settlement_safety_margin=UPTO_SETTLEMENT_SAFETY_MARGIN_SECONDS,
         session_cost_calculator=_session_cost_calculator,
     )
     logger.info(
diff --git a/tee_gateway/definitions.py b/tee_gateway/definitions.py
index d91ae8a..4b0b8c4 100644
--- a/tee_gateway/definitions.py
+++ b/tee_gateway/definitions.py
@@ -66,21 +66,53 @@
 # by compute_session_cost() in pricing.py.
 # ---------------------------------------------------------------------------
 
-# /v1/chat/completions — maximum OPG spend per session (18 decimals: 100000000000000000 = 0.1 OPG).
+# /v1/chat/completions — maximum OPG spend per session (18 decimals: 5000000000000000000 = 5 OPG).
 # This is the upper-bound amount presented to the client during the x402 pre-check handshake.
 # The x402 "upto" scheme allows the actual charge to be any value up to this cap;
 # the real per-request cost is settled dynamically by compute_session_cost() in pricing.py
 # based on actual token usage, so clients are never overcharged beyond what they consumed.
-CHAT_COMPLETIONS_OPG_SESSION_MAX_SPEND: str = "100000000000000000"
+CHAT_COMPLETIONS_OPG_SESSION_MAX_SPEND: str = "5000000000000000000"
 
 # /v1/ohttp — maximum OPG spend per session (18 decimals: 5000000000000000000 = 5 OPG).
 # OHTTP image-generation requests can be much more expensive than text chat,
 # so the relay-paid encrypted endpoint needs a higher per-session cap.
 OHTTP_OPG_SESSION_MAX_SPEND: str = "5000000000000000000"
 
-# /v1/completions — maximum OPG spend per session (18 decimals: 100000000000000000 = 0.1 OPG).
+# /v1/completions — maximum OPG spend per session (18 decimals: 5000000000000000000 = 5 OPG).
 # This is the upper-bound amount presented to the client during the x402 pre-check handshake.
 # The x402 "upto" scheme allows the actual charge to be any value up to this cap;
 # the real per-request cost is settled dynamically by compute_session_cost() in pricing.py
 # based on actual token usage, so clients are never overcharged beyond what they consumed.
-COMPLETIONS_OPG_SESSION_MAX_SPEND: str = "100000000000000000"
+COMPLETIONS_OPG_SESSION_MAX_SPEND: str = "5000000000000000000"
+
+# ---------------------------------------------------------------------------
+# x402 "upto" session settlement timing
+# ---------------------------------------------------------------------------
+# A draw-down ("upto") session reuses ONE signed Permit2 authorization whose
+# on-chain deadline is fixed at signing time (session creation) and never
+# refreshed. If the accumulated tab is settled after that deadline the on-chain
+# ``settle`` reverts and the whole session's payment is silently lost. These
+# knobs keep the settlement schedule safely inside the signed window.
+#
+# INVARIANT (must hold or long sessions drop payments):
+#     UPTO_SESSION_IDLE_TIMEOUT_SECONDS
+#         < UPTO_SETTLEMENT_SAFETY_MARGIN_SECONDS
+#         < UPTO_SESSION_MAX_TIMEOUT_SECONDS
+# and the safety margin must exceed SETTLEMENT_POLL_TIMEOUT_SECONDS so a
+# force-settled tab has time to confirm on-chain before the deadline.
+
+# Validity window signed into the Permit2 authorization (deadline = creation + this).
+# Advertised to clients as ``maxTimeoutSeconds`` in the 402 requirements.
+UPTO_SESSION_MAX_TIMEOUT_SECONDS: int = 600
+
+# Force-settle a session (and stop accepting new draw-downs against it) this many
+# seconds before its authorization deadline, leaving room for on-chain confirmation.
+UPTO_SETTLEMENT_SAFETY_MARGIN_SECONDS: int = 120
+
+# Settle a session once it has been idle (no new requests) this long.
+UPTO_SESSION_IDLE_TIMEOUT_SECONDS: int = 60
+
+# Deferred settlement is asynchronous on the facilitator (202 + job id). Poll the
+# job-status endpoint until the on-chain result is known instead of assuming success.
+SETTLEMENT_POLL_INTERVAL_SECONDS: float = 2.0
+SETTLEMENT_POLL_TIMEOUT_SECONDS: float = 100.0
diff --git a/tee_gateway/test/test_settlement_timing.py b/tee_gateway/test/test_settlement_timing.py
new file mode 100644
index 0000000..e72162c
--- /dev/null
+++ b/tee_gateway/test/test_settlement_timing.py
@@ -0,0 +1,60 @@
+"""Guard tests for the x402 "upto" session settlement timing constants.
+
+A draw-down ("upto") session reuses ONE signed Permit2 authorization whose
+on-chain deadline is fixed at session creation (created_at + max_timeout) and
+never refreshed. If the accumulated tab is settled after that deadline the
+on-chain ``settle`` reverts and the whole session's payment is silently lost.
+
+These tests lock in the ordering invariant between the settlement timing knobs
+so a future edit to definitions.py can't silently reintroduce the drop.
+"""
+
+from tee_gateway.definitions import (
+    SETTLEMENT_POLL_TIMEOUT_SECONDS,
+    UPTO_SESSION_IDLE_TIMEOUT_SECONDS,
+    UPTO_SESSION_MAX_TIMEOUT_SECONDS,
+    UPTO_SETTLEMENT_SAFETY_MARGIN_SECONDS,
+)
+
+
+def test_timing_constants_are_positive():
+    """Every timing knob must be a positive duration."""
+    assert UPTO_SESSION_IDLE_TIMEOUT_SECONDS > 0
+    assert UPTO_SETTLEMENT_SAFETY_MARGIN_SECONDS > 0
+    assert UPTO_SESSION_MAX_TIMEOUT_SECONDS > 0
+    assert SETTLEMENT_POLL_TIMEOUT_SECONDS > 0
+
+
+def test_idle_timeout_below_safety_margin():
+    """An idle session must settle (idle timeout) well before the force-settle
+    safety window, so normal traffic settles via idle and never races the
+    deadline."""
+    assert UPTO_SESSION_IDLE_TIMEOUT_SECONDS < UPTO_SETTLEMENT_SAFETY_MARGIN_SECONDS
+
+
+def test_safety_margin_below_max_timeout():
+    """The force-settle point (deadline - safety_margin) must be strictly before
+    the authorization deadline, leaving a positive window to settle in."""
+    assert UPTO_SETTLEMENT_SAFETY_MARGIN_SECONDS < UPTO_SESSION_MAX_TIMEOUT_SECONDS
+
+
+def test_safety_margin_covers_poll_timeout():
+    """Force-settling starts safety_margin seconds before the deadline, and the
+    reaper then polls the facilitator for up to SETTLEMENT_POLL_TIMEOUT_SECONDS
+    to confirm the on-chain result. The margin must exceed the poll timeout so a
+    force-settled tab can confirm before its authorization expires."""
+    assert UPTO_SETTLEMENT_SAFETY_MARGIN_SECONDS > SETTLEMENT_POLL_TIMEOUT_SECONDS
+
+
+def test_full_ordering_invariant():
+    """The complete invariant documented in definitions.py, in one assertion:
+
+    poll_timeout < safety_margin < max_timeout
+    idle_timeout < safety_margin
+    """
+    assert (
+        UPTO_SESSION_IDLE_TIMEOUT_SECONDS
+        < UPTO_SETTLEMENT_SAFETY_MARGIN_SECONDS
+        < UPTO_SESSION_MAX_TIMEOUT_SECONDS
+    )
+    assert SETTLEMENT_POLL_TIMEOUT_SECONDS < UPTO_SETTLEMENT_SAFETY_MARGIN_SECONDS