diff --git a/llmage/balance.py b/llmage/balance.py
new file mode 100644
index 0000000..76aa840
--- /dev/null
+++ b/llmage/balance.py
@@ -0,0 +1,250 @@
+"""
+Redis atomic balance reservation for llmage.
+Prevents concurrent overspend: pre-deduct before inference, settle after accounting.
+
+Key patterns:
+  balance:{userorgid}           — current pre-deducted balance (int, cents)
+  reserve:{luid}                — {userorgid}|{llmid}|{max_cost}  (TTL 600s)
+  model:max_cost:{llmid}        — historical max actual customer charge (int, cents)
+"""
+import asyncio
+from appPublic.log import debug, exception
+
+# ── Lua scripts ──────────────────────────────────────────────
+
+RESERVE_LUA = """
+local bal_key = KEYS[1]
+local cost_key = KEYS[2]
+local reserve_key = KEYS[3]
+local max_cost = tonumber(ARGV[1])
+local db_balance = tonumber(ARGV[2])    -- 0 means no DB fallback
+local reserve_val = ARGV[3]
+
+-- Get or init max_cost: use stored if higher, else set from arg
+local stored_max = redis.call('GET', cost_key)
+if stored_max then
+    max_cost = math.max(max_cost, tonumber(stored_max))
+elseif max_cost > 0 then
+    redis.call('SET', cost_key, max_cost)
+end
+if max_cost <= 0 then
+    return {0, 'max_cost is zero'}
+end
+
+-- Load or init balance
+local balance = redis.call('GET', bal_key)
+if not balance then
+    if db_balance > 0 then
+        balance = db_balance
+        redis.call('SET', bal_key, db_balance)
+    else
+        return {0, 'balance not initialized'}
+    end
+end
+balance = tonumber(balance)
+
+-- Check and deduct
+if balance < max_cost then
+    return {0, 'insufficient balance'}
+end
+redis.call('DECRBY', bal_key, max_cost)
+redis.call('SETEX', reserve_key, 600, reserve_val)
+return {1, max_cost}
+"""
+
+FINALIZE_LUA = """
+local cost_key = KEYS[1]
+local reserve_key = KEYS[2]
+local actual_cost = tonumber(ARGV[1])
+
+-- Atomically pop reserve
+local reserve_val = redis.call('GETDEL', reserve_key)
+if not reserve_val then
+    return {0, 'no reserve'}
+end
+
+-- Parse: userorgid|llmid|max_cost
+local i = 1
+local userorgid, llmid, max_cost
+for part in string.gmatch(reserve_val, '([^|]+)') do
+    if i == 1 then userorgid = part
+    elseif i == 2 then llmid = part
+    elseif i == 3 then max_cost = tonumber(part) end
+    i = i + 1
+end
+
+-- Update max_cost if actual exceeds
+if actual_cost > max_cost then
+    redis.call('SET', cost_key, actual_cost)
+    max_cost = actual_cost
+end
+
+-- Adjust balance
+local bal_key = 'balance:' .. userorgid
+local diff = max_cost - actual_cost
+if diff > 0 then
+    redis.call('INCRBY', bal_key, diff)
+elseif diff < 0 then
+    redis.call('DECRBY', bal_key, -diff)
+end
+
+return {1, userorgid, max_cost, actual_cost, diff}
+"""
+
+REFUND_LUA = """
+local reserve_key = KEYS[1]
+
+local reserve_val = redis.call('GETDEL', reserve_key)
+if not reserve_val then
+    return {0, 'no reserve'}
+end
+
+local i = 1
+local userorgid, llmid, max_cost
+for part in string.gmatch(reserve_val, '([^|]+)') do
+    if i == 1 then userorgid = part
+    elseif i == 2 then llmid = part
+    elseif i == 3 then max_cost = tonumber(part) end
+    i = i + 1
+end
+
+if max_cost > 0 then
+    redis.call('INCRBY', 'balance:' .. userorgid, max_cost)
+end
+return {1, max_cost, userorgid}
+"""
+
+
+def _cents(f):
+    return int(round(float(f) * 100))
+
+
+def _from_cents(c):
+    return round(int(c) / 100, 2)
+
+
+async def _redis_eval(env, script, nkeys, *keys_and_args):
+    """Eval Lua script via env's Redis connection."""
+    if not hasattr(env, 'redis') or env.redis is None:
+        raise RuntimeError('Redis unavailable')
+    return await asyncio.to_thread(env.redis.eval, script, nkeys, *keys_and_args)
+
+
+async def reserve_balance(env, llmid, userorgid, luid):
+    """Atomically check balance and deduct max_cost via Redis Lua."""
+    try:
+        bal_key = f'balance:{userorgid}'
+        cost_key = f'model:max_cost:{llmid}'
+        reserve_key = f'reserve:{luid}'
+        
+        # Load max_cost from DB if not cached
+        redis = env.redis
+        max_cost = 0
+        stored = await asyncio.to_thread(redis.get, cost_key)
+        if stored:
+            max_cost = int(stored)
+        else:
+            try:
+                from .utils import get_model_max_cost
+                mc = await get_model_max_cost(llmid)
+                if mc and mc > 0:
+                    max_cost = _cents(mc)
+            except Exception as e:
+                debug(f'reserve_balance: get_model_max_cost failed: {e}')
+        
+        if max_cost <= 0:
+            return {'ok': True, 'max_cost': 0, 'no_history': True}
+        
+        # Load balance from DB if not cached
+        db_balance = 0
+        stored_bal = await asyncio.to_thread(redis.get, bal_key)
+        if not stored_bal:
+            try:
+                from accounting.getaccount import getCustomerBalance
+                from sqlor.dbpools import get_sor_context
+                async with get_sor_context(env, 'accounting') as sor:
+                    bal = await getCustomerBalance(sor, userorgid)
+                    if bal is not None:
+                        db_balance = _cents(float(bal))
+            except Exception as e:
+                debug(f'reserve_balance: getCustomerBalance failed: {e}')
+        
+        reserve_val = f'{userorgid}|{llmid}|{max_cost}'
+        result = await _redis_eval(env, RESERVE_LUA, 3,
+            bal_key, cost_key, reserve_key,
+            str(max_cost), str(db_balance), reserve_val)
+        
+        if result[0] == 0:
+            return {'ok': False, 'reason': result[1]}
+        return {'ok': True, 'max_cost': _from_cents(result[1])}
+    
+    except RuntimeError:
+        debug('reserve_balance: Redis unavailable, skip')
+        return {'ok': True, 'max_cost': 0, 'no_redis': True}
+    except Exception as e:
+        exception(f'reserve_balance error: {e}')
+        return {'ok': False, 'reason': str(e)}
+
+
+async def finalize_balance(env, luid, actual_cost):
+    """After accounting: adjust balance, update max_cost."""
+    try:
+        cost_key = 'model:max_cost:dummy'
+        reserve_key = f'reserve:{luid}'
+        
+        # We need the llmid to get the correct cost_key, but we won't know it
+        # until parsing the reserve. So use a placeholder and let Lua handle it.
+        # Actually FINALIZE_LUA only uses cost_key for updating, so pass a dummy.
+        # The real cost_key needs the llmid which comes from reserve parsing.
+        
+        redis = env.redis
+        reserve_val = await asyncio.to_thread(redis.get, reserve_key)
+        if not reserve_val:
+            debug(f'finalize_balance: no reserve for luid={luid}')
+            return
+        
+        # Parse to get llmid
+        parts = reserve_val.split('|')
+        if len(parts) < 3:
+            return
+        llmid = parts[1]
+        cost_key = f'model:max_cost:{llmid}'
+        
+        result = await _redis_eval(env, FINALIZE_LUA, 2,
+            cost_key, reserve_key, str(_cents(actual_cost)))
+        
+        if result[0] == 0:
+            debug(f'finalize_balance: {result[1]}')
+            return
+        
+        max_c = _from_cents(result[2])
+        diff = _from_cents(result[4])
+        debug(f'finalize_balance: luid={luid} max={max_c} actual={actual_cost} diff={diff}')
+        
+        # Persist max_cost to DB if actual exceeded previous max
+        if actual_cost > max_c:
+            try:
+                from .utils import update_model_max_cost
+                await update_model_max_cost(llmid, actual_cost)
+            except Exception as e:
+                debug(f'finalize_balance: DB persist failed: {e}')
+    
+    except RuntimeError:
+        debug('finalize_balance: Redis unavailable, skip')
+    except Exception as e:
+        exception(f'finalize_balance error: {e}')
+
+
+async def refund_balance(env, luid):
+    """Full refund on API failure."""
+    try:
+        reserve_key = f'reserve:{luid}'
+        result = await _redis_eval(env, REFUND_LUA, 1, reserve_key)
+        if result[0] == 1:
+            debug(f'refund_balance: luid={luid} refund={_from_cents(result[1])}')
+        else:
+            debug(f'refund_balance: luid={luid} skipped ({result[1]})')
+    except RuntimeError:
+        pass
+    except Exception as e:
+        exception(f'refund_balance error: {e}')
diff --git a/llmage/init.py b/llmage/init.py
index 864fbac..c8f9891 100644
--- a/llmage/init.py
+++ b/llmage/init.py
@@ -28,6 +28,10 @@ from .utils import (
 	get_llmid_cached,
 	invalidate_llmid_cache,
 	get_plaza_models,
+	# Redis balance reservation
+	reserve_balance,
+	finalize_balance,
+	refund_balance,
 )
 
 from .llmclient import (
@@ -166,6 +170,12 @@ def load_llmage():
 	env.llm_query_price = llm_query_price
 	env.get_llms_by_catelog_to_customer = get_llms_by_catelog_to_customer
 	env.get_plaza_models = get_plaza_models
+	env._reserve_balance = reserve_balance
+	env._finalize_balance = finalize_balance
+	env._refund_balance = refund_balance
+	env.reserve_balance = lambda llmid, userorgid, luid: reserve_balance(env, llmid, userorgid, luid)
+	env.finalize_balance = lambda luid, actual_cost: finalize_balance(env, luid, actual_cost)
+	env.refund_balance = lambda luid: refund_balance(env, luid)
 	env.backup_accounted_llmusage = backup_accounted_llmusage
 	env.read_ioinfo_content = read_ioinfo_content
 	env.get_llmusage_by_id = get_llmusage_by_id
diff --git a/llmage/utils.py b/llmage/utils.py
index 6b219fa..5514447 100644
--- a/llmage/utils.py
+++ b/llmage/utils.py
@@ -617,3 +617,24 @@ ServerEnv().os = _os
 ServerEnv().file_to_b64 = _file_to_b64
 ServerEnv().file_mime = _file_mime
 
+async def get_model_max_cost(llmid):
+	"""Get historical max actual customer charge for a model from llmusage."""
+	env = ServerEnv()
+	async with get_sor_context(env, 'llmage') as sor:
+		sql = """SELECT MAX(amount) as max_cost
+FROM llmusage
+WHERE llmid = ${llmid}$
+  AND status = 'SUCCEEDED'
+  AND amount IS NOT NULL
+  AND amount > 0"""
+		recs = await sor.sqlExe(sql, {'llmid': llmid})
+		if recs and recs[0].max_cost:
+			return float(recs[0].max_cost)
+	return 0
+
+async def update_model_max_cost(llmid, new_max):
+	"""Persist updated max_cost to llm table."""
+	env = ServerEnv()
+	async with get_sor_context(env, 'llmage') as sor:
+		await sor.U('llm', {'id': llmid, 'max_cost': float(new_max)})
+
diff --git a/wwwroot/v1/chat/completions/index.dspy b/wwwroot/v1/chat/completions/index.dspy
index 5105c21..466b5e8 100644
--- a/wwwroot/v1/chat/completions/index.dspy
+++ b/wwwroot/v1/chat/completions/index.dspy
@@ -1,13 +1,19 @@
 async def gen():
 	env = request._run_ns.copy()
 	f = partial(inference_generator, request, params_kw=params_kw)
-	if params_kw.stream:
-		async for l in f():
-			yield f'data: {l}\n'
-		yield 'data: [DONE]\n\n'
-	else:
-		async for l in f():
-			yield l
+	try:
+		if params_kw.stream:
+			async for l in f():
+				yield f'data: {l}\n'
+			yield 'data: [DONE]\n\n'
+		else:
+			async for l in f():
+				yield l
+	except Exception as e:
+		luid = params_kw.get('_luid')
+		if luid:
+			await env.refund_balance(luid)
+		raise
 
 debug_params('params_kw', params_kw)
 catelogid = params_kw.catelogid or 't2t'
@@ -37,9 +43,16 @@ params_kw.llmid = llmid
 	params_kw.llmcatelogid = catelogid
 
 debug(f'{params_kw.llmid=}')
+luid = getID()
+reserved = await env.reserve_balance(params_kw.llmid, userorgid, luid)
+if not reserved.get('ok'):
+	debug(f'{userid=} balance not enough: {reserved}')
+	return openai_429()
+params_kw._luid = luid
+params_kw._reserved = reserved
 f = await checkCustomerBalance(params_kw.llmid, userid, userorgid)
-if not f:
-	debug(f'{userid=} balance not enough')
+if not f and reserved.get('no_redis'):
+	debug(f'{userid=} balance not enough (DB fallback)')
 	return openai_429()
 # debug(f'{tools=}, {request._run_ns.tools=}')
 return await env.stream_response(request, gen, content_type='application/json')