diff --git a/packages/ai/CHANGELOG.md b/packages/ai/CHANGELOG.md
index 882ce5609..9d1b49309 100644
--- a/packages/ai/CHANGELOG.md
+++ b/packages/ai/CHANGELOG.md
@@ -28,6 +28,7 @@
 - Fixed pi-messages streams accepting a `contentIndex` that is not the next or an existing content block, such as `__proto__` or a huge index
 - Fixed `pi-ai` CLI auth file being readable by other users. It is now written with mode `0600`
 - Fixed OpenCode DeepSeek V4.1 Flash sending `prompt_cache_retention`, which the OpenCode gateway rejects, with long cache retention
+- Fixed GPT-5.4 and GPT-5.5 failing with `Missing namespace for function_call` after switching from another model that called tools. On the OpenAI and OpenCode providers they now declare their tools in the top-level tool list instead of loading them through `additional_tools` or tool search ([#11415](https://github.com/earendil-works/pi/issues/11415))
 
 ## [1.4.0] - 2026-10-21
 
diff --git a/packages/ai/scripts/generate-models.ts b/packages/ai/scripts/generate-models.ts
index b556d2505..966604358 100644
--- a/packages/ai/scripts/generate-models.ts
+++ b/packages/ai/scripts/generate-models.ts
@@ -366,11 +366,10 @@ const ANT_LING_RING_THINKING_LEVEL_MAP = {
 
 const BEDROCK_INFERENCE_PROFILE_ONLY_MODEL_IDS = new Set(["anthropic.claude-opus-5"]);
 const MODELS_DEV_OPENAI_UNSUPPORTED_MODEL_IDS = new Set(["gpt-5.6"]);
+// GPT-5.5 and older put tools loaded through tool search or additional_tools in a namespace named
+// after the tool and reject replayed calls without it, so history from other models fails there
+// (#11415). Like Codex, dynamic tool loading therefore starts with GPT-5.6, which does not do this.
 const OPENAI_TOOL_SEARCH_MODEL_IDS = new Set([
-	"gpt-5.4",
-	"gpt-5.4-mini",
-	"gpt-5.4-pro",
-	"gpt-5.5",
 	"gpt-5.6-sol",
 	"gpt-5.6-terra",
 	"gpt-5.6-luna",
@@ -381,7 +380,13 @@ const OPENAI_TOOL_SEARCH_MODEL_IDS = new Set([
 	"gpt-6.1-terra",
 ]);
 const OPENAI_ADDITIONAL_TOOLS_MODEL_IDS = OPENAI_TOOL_SEARCH_MODEL_IDS;
-const OPENAI_MID_CONVO_SYSTEM_MESSAGE_MODEL_IDS = OPENAI_TOOL_SEARCH_MODEL_IDS;
+const OPENAI_MID_CONVO_SYSTEM_MESSAGE_MODEL_IDS = new Set([
+	"gpt-5.4",
+	"gpt-5.4-mini",
+	"gpt-5.4-pro",
+	"gpt-5.5",
+	...OPENAI_TOOL_SEARCH_MODEL_IDS,
+]);
 const OPENAI_CODEX_ADDITIONAL_TOOLS_MODEL_IDS = new Set([
 	"gpt-5.6-sol",
 	"gpt-5.6-terra",
@@ -985,7 +990,7 @@ function applyOpenAIResponsesTranscriptMetadata(model: Model<Api>): void {
 	model.compat = {
 		...(model.compat as OpenAIResponsesCompat | undefined),
 		supportsMidConvoSystemMessages: true,
-		...(isProxiedResponses ? { supportsAdditionalTools: true } : {}),
+		...(isProxiedResponses && OPENAI_ADDITIONAL_TOOLS_MODEL_IDS.has(model.id) ? { supportsAdditionalTools: true } : {}),
 	};
 }
 
diff --git a/packages/ai/test/openai-responses-compat.test.ts b/packages/ai/test/openai-responses-compat.test.ts
index 3b61686e8..ec7783313 100644
--- a/packages/ai/test/openai-responses-compat.test.ts
+++ b/packages/ai/test/openai-responses-compat.test.ts
@@ -119,7 +119,7 @@ describe("openai-responses provider defaults", () => {
 		);
 
 		const stream = streamOpenAIResponses(
-			getModel("openai", "gpt-5.4"),
+			getModel("openai", "gpt-5.6-luna"),
 			normalizeContext({
 				messages: [
 					{
@@ -149,7 +149,7 @@ describe("openai-responses provider defaults", () => {
 			if (event.type === "done" || event.type === "error") break;
 		}
 
-		// gpt-5.4 declares its tools in additional_tools items; tool_choice applies to them.
+		// gpt-5.6-luna declares its tools in additional_tools items; tool_choice applies to them.
 		expect(capturedPayload).toMatchObject({
 			tool_choice: "required",
 			input: [{ type: "additional_tools", tools: [expect.objectContaining({ name: "ping" })] }, expect.anything()],