diff --git a/src/daemon/http/index.ts b/src/daemon/http/index.ts
index cbf9d2e..e49bedc 100644
--- a/src/daemon/http/index.ts
+++ b/src/daemon/http/index.ts
@@ -325,6 +325,8 @@ export function createDaemonRequestHandler(deps: {
   getModelProviders: (modelId: string) => Promise<any>;
   refreshProvidersAndModels: () => Promise<void>;
   mode?: "xcashu" | "apikeys";
+  /** Default max_tokens/max_output_tokens to inject when the client omits one. */
+  maxTokens: number;
   /** Nostr hex pubkey for routstr review/model events (kind 38425/38423). */
   routstrPubkey?: string;
   usageTrackingDriver: UsageTrackingDriver;
@@ -1486,6 +1488,22 @@ export function createDaemonRequestHandler(deps: {
       return;
     }
 
+    // Cap the completion budget when the client does not set an output token
+    // limit. Without this, the SDK prices at the provider's worst-case
+    // max_completion_cost, which varies widely across providers (2.3× for
+    // kimi-k3) and balloons during provider failover. Chat/completions use
+    // max_tokens; the OpenAI Responses API uses max_output_tokens.
+    if (deps.maxTokens > 0) {
+      const isResponsesPath = url.pathname.includes("/responses");
+      if (isResponsesPath) {
+        if (typeof bodyObj.max_output_tokens !== "number") {
+          bodyObj.max_output_tokens = deps.maxTokens;
+        }
+      } else if (typeof bodyObj.max_tokens !== "number") {
+        bodyObj.max_tokens = deps.maxTokens;
+      }
+    }
+
     const forcedProvider: string | undefined =
       url.searchParams.get("provider") ||
       (req.headers["x-routstr-provider"] as string | undefined) ||
diff --git a/src/daemon/index.ts b/src/daemon/index.ts
index 6475874..ed5021d 100644
--- a/src/daemon/index.ts
+++ b/src/daemon/index.ts
@@ -217,6 +217,7 @@ async function main(): Promise<void> {
       getModelProviders,
       refreshProvidersAndModels,
       mode: config.mode || "apikeys",
+      maxTokens: config.maxTokens ?? 64000,
       routstrPubkey: config.routstrPubkey,
       usageTrackingDriver,
       providerManager,
diff --git a/src/utils/config.ts b/src/utils/config.ts
index 2ebe28f..49a193e 100644
--- a/src/utils/config.ts
+++ b/src/utils/config.ts
@@ -55,6 +55,14 @@ export interface RoutstrdConfig {
   relays?: string[];
   /** NWC integration configuration */
   nwc?: NwcConfig;
+  /**
+   * Default max_tokens (chat/completions) and max_output_tokens (responses)
+   * injected into proxied requests when the client does not supply one.
+   * Caps the completion budget the SDK prices against (completion × maxTokens)
+   * instead of the provider's worst-case max_completion_cost. Set to 0 to
+   * disable injection and always forward the client's value as-is.
+   */
+  maxTokens?: number;
 }
 
 export const DEFAULT_CONFIG: RoutstrdConfig = {
@@ -63,4 +71,5 @@ export const DEFAULT_CONFIG: RoutstrdConfig = {
   provider: null,
   cocodPath: null,
   mode: "apikeys",
+  maxTokens: 64000,
 };