diff --git a/packages/agent/CHANGELOG.md b/packages/agent/CHANGELOG.md
index d158ba19..05cf0810 100644
--- a/packages/agent/CHANGELOG.md
+++ b/packages/agent/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 ### Fixed
 
+- Fixed `streamProxy()` to preserve the proxy-safe serializable subset of stream options, including session, transport, retry-delay, metadata, header, cache-retention, and thinking-budget settings ([#3512](https://github.com/badlogic/pi-mono/issues/3512))
 - Fixed parallel tool execution to emit `tool_execution_end` as soon as each tool is finalized, while still emitting persisted tool-result messages in assistant source order ([#3503](https://github.com/badlogic/pi-mono/issues/3503))
 
 ## [0.68.0] - 2026-04-20
diff --git a/packages/agent/src/proxy.ts b/packages/agent/src/proxy.ts
index dfa72c73..a7830477 100644
--- a/packages/agent/src/proxy.ts
+++ b/packages/agent/src/proxy.ts
@@ -56,7 +56,23 @@ export type ProxyAssistantMessageEvent =
 			usage: AssistantMessage["usage"];
 	  };
 
-export interface ProxyStreamOptions extends SimpleStreamOptions {
+type ProxySerializableStreamOptions = Pick<
+	SimpleStreamOptions,
+	| "temperature"
+	| "maxTokens"
+	| "reasoning"
+	| "cacheRetention"
+	| "sessionId"
+	| "headers"
+	| "metadata"
+	| "transport"
+	| "thinkingBudgets"
+	| "maxRetryDelayMs"
+>;
+
+export interface ProxyStreamOptions extends ProxySerializableStreamOptions {
+	/** Local abort signal for the proxy request */
+	signal?: AbortSignal;
 	/** Auth token for the proxy server */
 	authToken: string;
 	/** Proxy server URL (e.g., "https://genai.example.com") */
@@ -82,6 +98,21 @@ export interface ProxyStreamOptions extends SimpleStreamOptions {
  * });
  * ```
  */
+function buildProxyRequestOptions(options: ProxyStreamOptions): ProxySerializableStreamOptions {
+	return {
+		temperature: options.temperature,
+		maxTokens: options.maxTokens,
+		reasoning: options.reasoning,
+		cacheRetention: options.cacheRetention,
+		sessionId: options.sessionId,
+		headers: options.headers,
+		metadata: options.metadata,
+		transport: options.transport,
+		thinkingBudgets: options.thinkingBudgets,
+		maxRetryDelayMs: options.maxRetryDelayMs,
+	};
+}
+
 export function streamProxy(model: Model<any>, context: Context, options: ProxyStreamOptions): ProxyMessageEventStream {
 	const stream = new ProxyMessageEventStream();
 
@@ -127,11 +158,7 @@ export function streamProxy(model: Model<any>, context: Context, options: ProxyS
 				body: JSON.stringify({
 					model,
 					context,
-					options: {
-						temperature: options.temperature,
-						maxTokens: options.maxTokens,
-						reasoning: options.reasoning,
-					},
+					options: buildProxyRequestOptions(options),
 				}),
 				signal: options.signal,
 			});