diff --git a/packages/ai/src/protocols/gemini.ts b/packages/ai/src/protocols/gemini.ts
index 1252885335f..eb0536e9c4f 100644
--- a/packages/ai/src/protocols/gemini.ts
+++ b/packages/ai/src/protocols/gemini.ts
@@ -41,6 +41,13 @@ const requiresThoughtSignatureFallback = (modelID: string) => {
 // so their tool-result attachments lower as a separate user turn instead.
 const routesLegacyToolMedia = (modelID: string) => /gemini-2[.-]5(?:[.-]|$)/i.test(modelID)
 
+// Blacklist: Gemini 1.x/2.x ignore or reject explicit function call ids.
+// Every other model id (Gemini 3+, gemma, anything unrecognized) gets them.
+const omitsFunctionCallIds = (modelID: string) => {
+  const match = /^gemini(?:-live)?-(\d+)/i.exec(modelID)
+  return match !== null && Number(match[1]) < 3
+}
+
 export interface OptionsInput {
   readonly [key: string]: unknown
   readonly cachedContent?: string
@@ -217,6 +224,7 @@ interface ParserState {
   readonly lifecycle: Lifecycle.State
   readonly reasoningSignature?: string
   readonly textSignature?: string
+  readonly seenCallIds?: ReadonlySet<string>
 }
 
 // =============================================================================
@@ -274,20 +282,14 @@ const thoughtSignature = (providerMetadata: ProviderMetadata | undefined) => {
     : undefined
 }
 
-const functionCallId = (providerMetadata: ProviderMetadata | undefined) => {
-  const google = providerMetadata?.google
-  return ProviderShared.isRecord(google) && typeof google.functionCallId === "string"
-    ? google.functionCallId
-    : undefined
-}
-
-const lowerToolCall = (part: ToolCallPart) => ({
-  functionCall: { id: functionCallId(part.providerMetadata), name: part.name, args: part.input },
+const lowerToolCall = (part: ToolCallPart, omitIds: boolean) => ({
+  functionCall: { ...(omitIds ? {} : { id: part.id }), name: part.name, args: part.input },
   thoughtSignature: thoughtSignature(part.providerMetadata),
 })
 
 const lowerMessages = Effect.fn("Gemini.lowerMessages")(function* (request: LLMRequest) {
   const contents: GeminiContent[] = []
+  const omitCallIds = omitsFunctionCallIds(request.model.id)
   const legacyToolMedia = routesLegacyToolMedia(request.model.id)
   let pendingMedia: GeminiInlineDataPart[] | undefined
   const flushMedia = () => {
@@ -336,7 +338,7 @@ const lowerMessages = Effect.fn("Gemini.lowerMessages")(function* (request: LLMR
           continue
         }
         if (part.type === "tool-call") {
-          const lowered = lowerToolCall(part)
+          const lowered = lowerToolCall(part, omitCallIds)
           const signature = lowered.thoughtSignature
           parts.push({
             ...lowered,
@@ -361,7 +363,7 @@ const lowerMessages = Effect.fn("Gemini.lowerMessages")(function* (request: LLMR
       if (part.result.type !== "content") {
         parts.push({
           functionResponse: {
-            id: functionCallId(part.providerMetadata),
+            ...(omitCallIds ? {} : { id: part.id }),
             name: part.name,
             response: {
               name: part.name,
@@ -382,7 +384,7 @@ const lowerMessages = Effect.fn("Gemini.lowerMessages")(function* (request: LLMR
       if (legacyToolMedia && media.length > 0) (pendingMedia ??= []).push(...media)
       parts.push({
         functionResponse: {
-          id: functionCallId(part.providerMetadata),
+          ...(omitCallIds ? {} : { id: part.id }),
           name: part.name,
           response: {
             name: part.name,
@@ -581,6 +583,8 @@ const step = (state: ParserState, event: GeminiEvent) => {
   let lifecycle = nextState.lifecycle
   let reasoningSignature = nextState.reasoningSignature
   let textSignature = nextState.textSignature
+  // Supplier ids must be tracked across chunks of the same response, not just within one event's parts.
+  const seenCallIds = new Set(nextState.seenCallIds)
 
   for (const part of candidate.content.parts) {
     const signature = "thoughtSignature" in part && part.thoughtSignature ? part.thoughtSignature : undefined
@@ -618,13 +622,13 @@ const step = (state: ParserState, event: GeminiEvent) => {
 
     if ("functionCall" in part) {
       const input = part.functionCall.args === undefined ? {} : part.functionCall.args
-      // Gemini 2.0+ and Vertex supply a unique function call ID on the part; when omitted (e.g. Gemini 1.5),
+      // Gemini 2.0+ supplies a unique function call ID on the part; when omitted (e.g. Gemini 1.5),
       // generate a globally unique ID rather than a per-request counter to prevent cross-request collisions in downstream registries.
-      const id = part.functionCall.id ?? `tool_${crypto.randomUUID().replaceAll("-", "")}`
-      const metadata = {
-        ...(part.functionCall.id === undefined ? {} : { functionCallId: part.functionCall.id }),
-        ...(part.thoughtSignature === undefined ? {} : { thoughtSignature: part.thoughtSignature }),
-      }
+      // A repeated supplier id would replay as two identical calls, so only the first occurrence keeps it.
+      const supplied = part.functionCall.id
+      const duplicate = supplied !== undefined && seenCallIds.has(supplied)
+      if (supplied !== undefined) seenCallIds.add(supplied)
+      const id = supplied !== undefined && !duplicate ? supplied : `tool_${crypto.randomUUID().replaceAll("-", "")}`
       lifecycle = Lifecycle.reasoningEnd(
         lifecycle,
         events,
@@ -637,7 +641,8 @@ const step = (state: ParserState, event: GeminiEvent) => {
           id,
           name: part.functionCall.name,
           input,
-          providerMetadata: Object.keys(metadata).length > 0 ? googleMetadata(metadata) : undefined,
+          providerMetadata:
+            part.thoughtSignature === undefined ? undefined : googleMetadata({ thoughtSignature: part.thoughtSignature }),
         }),
       )
       hasToolCalls = true
@@ -651,6 +656,7 @@ const step = (state: ParserState, event: GeminiEvent) => {
       lifecycle,
       reasoningSignature,
       textSignature,
+      seenCallIds,
       finishReason: candidate.finishReason ?? nextState.finishReason,
     },
     events,
diff --git a/packages/ai/src/providers/google-vertex.ts b/packages/ai/src/providers/google-vertex.ts
index e0bf9357303..20f816997ee 100644
--- a/packages/ai/src/providers/google-vertex.ts
+++ b/packages/ai/src/providers/google-vertex.ts
@@ -38,13 +38,23 @@ export type Settings = ProviderPackage.Settings &
 
 const fromRequest = Effect.fn("GoogleVertex.fromRequest")(function* (request: LLMRequest) {
   const body = yield* Gemini.protocol.body.from(request)
+  // Vertex's native REST schema rejects `id` on FunctionCall/FunctionResponse parts with HTTP 400,
+  // unlike AI Studio, so history minted there cannot be lowered verbatim.
+  const contents = body.contents.map((content) => ({
+    ...content,
+    parts: content.parts.map((part) => {
+      if ("functionCall" in part) return { ...part, functionCall: { ...part.functionCall, id: undefined } }
+      if ("functionResponse" in part) return { ...part, functionResponse: { ...part.functionResponse, id: undefined } }
+      return part
+    }),
+  }))
   const value = request.providerOptions?.labels
   const labels = ProviderShared.isRecord(value)
     ? Object.fromEntries(
         Object.entries(value).filter((entry): entry is [string, string] => typeof entry[1] === "string"),
       )
     : undefined
-  return { ...body, labels }
+  return { ...body, contents, labels }
 })
 
 const protocol = {
diff --git a/packages/ai/test/fixtures/recordings/azure/chat-streams-text.json b/packages/ai/test/fixtures/recordings/azure/chat-streams-text.json
new file mode 100644
index 00000000000..0dc0816b326
--- /dev/null
+++ b/packages/ai/test/fixtures/recordings/azure/chat-streams-text.json
@@ -0,0 +1,31 @@
+{
+  "version": 1,
+  "metadata": {
+    "tags": [
+      "prefix:azure",
+      "provider:azure"
+    ],
+    "name": "azure/chat-streams-text",
+    "recordedAt": "2026-08-23T17:21:53.198Z"
+  },
+  "interactions": [
+    {
+      "transport": "http",
+      "request": {
+        "method": "POST",
+        "url": "https://aiden-azury-group.openai.azure.com/openai/v1/chat/completions?api-version=v1",
+        "headers": {
+          "content-type": "application/json"
+        },
+        "body": "{\"model\":\"gpt-5.6-luna\",\"messages\":[{\"role\":\"user\",\"content\":\"Reply with exactly one word: hello\"}],\"stream\":true,\"stream_options\":{\"include_usage\":true},\"store\":false,\"reasoning_effort\":\"medium\"}"
+      },
+      "response": {
+        "status": 200,
+        "headers": {
+          "content-type": "text/event-stream; charset=utf-8"
+        },
+        "body": "data: {\"choices\":[],\"created\":0,\"id\":\"\",\"model\":\"\",\"object\":\"\",\"prompt_filter_results\":[{\"prompt_index\":0,\"content_filter_results\":{}}]}\n\ndata: {\"choices\":[{\"content_filter_results\":{},\"delta\":{\"content\":\"\",\"refusal\":null,\"role\":\"assistant\"},\"finish_reason\":null,\"index\":0,\"logprobs\":null}],\"created\":1787505712,\"id\":\"chatcmpl-EG6BEiYSfrcTSI2WX8PqNzERZDcPc\",\"model\":\"gpt-5.6-luna-2026-07-09\",\"obfuscation\":\"Mxr\",\"object\":\"chat.completion.chunk\",\"service_tier\":\"default\",\"system_fingerprint\":null,\"usage\":null}\n\ndata: {\"choices\":[{\"content_filter_results\":{},\"delta\":{\"content\":\"hello\"},\"finish_reason\":null,\"index\":0,\"logprobs\":null}],\"created\":1787505712,\"id\":\"chatcmpl-EG6BEiYSfrcTSI2WX8PqNzERZDcPc\",\"model\":\"gpt-5.6-luna-2026-07-09\",\"obfuscation\":\"\",\"object\":\"chat.completion.chunk\",\"service_tier\":\"default\",\"system_fingerprint\":null,\"usage\":null}\n\ndata: {\"choices\":[{\"content_filter_results\":{},\"delta\":{},\"finish_reason\":\"stop\",\"index\":0,\"logprobs\":null}],\"created\":1787505712,\"id\":\"chatcmpl-EG6BEiYSfrcTSI2WX8PqNzERZDcPc\",\"model\":\"gpt-5.6-luna-2026-07-09\",\"obfuscation\":\"WyZa5AY1CaCeFdS\",\"object\":\"chat.completion.chunk\",\"service_tier\":\"default\",\"system_fingerprint\":null,\"usage\":null}\n\ndata: {\"choices\":[],\"created\":1787505712,\"id\":\"chatcmpl-EG6BEiYSfrcTSI2WX8PqNzERZDcPc\",\"latency_checkpoint\":{\"engine_tbt_ms\":20,\"engine_ttft_ms\":106,\"engine_ttlt_ms\":206,\"pre_inference_ms\":89,\"service_tbt_ms\":20,\"service_ttft_ms\":480,\"service_ttlt_ms\":576,\"total_duration_ms\":491,\"user_visible_ttft_ms\":391},\"model\":\"gpt-5.6-luna-2026-07-09\",\"obfuscation\":\"6\",\"object\":\"chat.completion.chunk\",\"service_tier\":\"default\",\"system_fingerprint\":null,\"usage\":{\"completion_tokens\":5,\"completion_tokens_details\":{\"accepted_prediction_tokens\":0,\"audio_tokens\":0,\"reasoning_tokens\":0,\"rejected_prediction_tokens\":0},\"prompt_tokens\":13,\"prompt_tokens_details\":{\"audio_tokens\":0,\"cache_write_tokens\":0,\"cached_tokens\":0},\"total_tokens\":18}}\n\ndata: [DONE]\n\n"
+      }
+    }
+  ]
+}
diff --git a/packages/ai/test/fixtures/recordings/azure/responses-calls-a-tool.json b/packages/ai/test/fixtures/recordings/azure/responses-calls-a-tool.json
new file mode 100644
index 00000000000..2c349382505
--- /dev/null
+++ b/packages/ai/test/fixtures/recordings/azure/responses-calls-a-tool.json
@@ -0,0 +1,31 @@
+{
+  "version": 1,
+  "metadata": {
+    "tags": [
+      "prefix:azure",
+      "provider:azure"
+    ],
+    "name": "azure/responses-calls-a-tool",
+    "recordedAt": "2026-08-23T17:21:55.170Z"
+  },
+  "interactions": [
+    {
+      "transport": "http",
+      "request": {
+        "method": "POST",
+        "url": "https://aiden-azury-group.openai.azure.com/openai/v1/responses?api-version=v1",
+        "headers": {
+          "content-type": "application/json"
+        },
+        "body": "{\"model\":\"gpt-5.6-luna\",\"input\":[{\"role\":\"user\",\"content\":[{\"type\":\"input_text\",\"text\":\"What is the weather in Paris? Use the lookup_weather tool.\"}]}],\"tools\":[{\"type\":\"function\",\"name\":\"lookup_weather\",\"description\":\"Look up the current weather for a city\",\"parameters\":{\"type\":\"object\",\"properties\":{\"city\":{\"type\":\"string\"}},\"required\":[\"city\"]},\"strict\":false}],\"store\":false,\"include\":[\"reasoning.encrypted_content\"],\"reasoning\":{\"effort\":\"medium\",\"summary\":\"auto\"},\"stream\":true}"
+      },
+      "response": {
+        "status": 200,
+        "headers": {
+          "content-type": "text/event-stream; charset=utf-8"
+        },
+        "body": "event: response.created\ndata: {\"type\":\"response.created\",\"response\":{\"id\":\"resp_038668c35ae811d3016a8b2c3273888196a6e34efef3bd3193\",\"object\":\"response\",\"created_at\":1787505714,\"status\":\"in_progress\",\"background\":false,\"completed_at\":null,\"content_filters\":null,\"error\":null,\"frequency_penalty\":0.0,\"incomplete_details\":null,\"instructions\":null,\"max_output_tokens\":null,\"max_tool_calls\":null,\"model\":\"gpt-5.6-luna\",\"moderation\":null,\"output\":[],\"parallel_tool_calls\":true,\"presence_penalty\":0.0,\"previous_response_id\":null,\"prompt_cache_key\":null,\"prompt_cache_retention\":\"24h\",\"reasoning\":{\"context\":\"all_turns\",\"effort\":\"medium\",\"mode\":\"standard\",\"summary\":\"detailed\"},\"safety_identifier\":null,\"service_tier\":\"auto\",\"store\":false,\"temperature\":1.0,\"text\":{\"format\":{\"type\":\"text\"},\"verbosity\":\"medium\"},\"tool_choice\":\"auto\",\"tool_usage\":{\"image_gen\":{\"input_tokens\":0,\"input_tokens_details\":{\"image_tokens\":0,\"text_tokens\":0},\"output_tokens\":0,\"output_tokens_details\":{\"image_tokens\":0,\"text_tokens\":0},\"total_tokens\":0},\"web_search\":{\"num_requests\":0}},\"tools\":[{\"type\":\"function\",\"description\":\"Look up the current weather for a city\",\"name\":\"lookup_weather\",\"output_schema\":null,\"parameters\":{\"type\":\"object\",\"properties\":{\"city\":{\"type\":\"string\"}},\"required\":[\"city\"]},\"strict\":false}],\"top_logprobs\":0,\"top_p\":0.98,\"truncation\":\"disabled\",\"usage\":null,\"user\":null,\"metadata\":{}},\"sequence_number\":0}\n\nevent: response.in_progress\ndata: {\"type\":\"response.in_progress\",\"response\":{\"id\":\"resp_038668c35ae811d3016a8b2c3273888196a6e34efef3bd3193\",\"object\":\"response\",\"created_at\":1787505714,\"status\":\"in_progress\",\"background\":false,\"completed_at\":null,\"content_filters\":null,\"error\":null,\"frequency_penalty\":0.0,\"incomplete_details\":null,\"instructions\":null,\"max_output_tokens\":null,\"max_tool_calls\":null,\"model\":\"gpt-5.6-luna\",\"moderation\":null,\"output\":[],\"parallel_tool_calls\":true,\"presence_penalty\":0.0,\"previous_response_id\":null,\"prompt_cache_key\":null,\"prompt_cache_retention\":\"24h\",\"reasoning\":{\"context\":\"all_turns\",\"effort\":\"medium\",\"mode\":\"standard\",\"summary\":\"detailed\"},\"safety_identifier\":null,\"service_tier\":\"auto\",\"store\":false,\"temperature\":1.0,\"text\":{\"format\":{\"type\":\"text\"},\"verbosity\":\"medium\"},\"tool_choice\":\"auto\",\"tool_usage\":{\"image_gen\":{\"input_tokens\":0,\"input_tokens_details\":{\"image_tokens\":0,\"text_tokens\":0},\"output_tokens\":0,\"output_tokens_details\":{\"image_tokens\":0,\"text_tokens\":0},\"total_tokens\":0},\"web_search\":{\"num_requests\":0}},\"tools\":[{\"type\":\"function\",\"description\":\"Look up the current weather for a city\",\"name\":\"lookup_weather\",\"output_schema\":null,\"parameters\":{\"type\":\"object\",\"properties\":{\"city\":{\"type\":\"string\"}},\"required\":[\"city\"]},\"strict\":false}],\"top_logprobs\":0,\"top_p\":0.98,\"truncation\":\"disabled\",\"usage\":null,\"user\":null,\"metadata\":{}},\"sequence_number\":1}\n\nevent: response.output_item.added\ndata: {\"type\":\"response.output_item.added\",\"item\":{\"id\":\"fc_038668c35ae811d3016a8b2c332090819687d2f367bda0452b\",\"type\":\"function_call\",\"status\":\"in_progress\",\"arguments\":\"\",\"call_id\":\"call_urtlVDzFCdgMMgPqZHCTGmEL\",\"name\":\"lookup_weather\"},\"output_index\":0,\"sequence_number\":2}\n\nevent: response.function_call_arguments.delta\ndata: {\"type\":\"response.function_call_arguments.delta\",\"delta\":\"{\\\"\",\"item_id\":\"fc_038668c35ae811d3016a8b2c332090819687d2f367bda0452b\",\"obfuscation\":\"APjMzP58C5JCVD\",\"output_index\":0,\"sequence_number\":3}\n\nevent: response.function_call_arguments.delta\ndata: {\"type\":\"response.function_call_arguments.delta\",\"delta\":\"city\",\"item_id\":\"fc_038668c35ae811d3016a8b2c332090819687d2f367bda0452b\",\"obfuscation\":\"zoCPWwIaPzzU\",\"output_index\":0,\"sequence_number\":4}\n\nevent: response.function_call_arguments.delta\ndata: {\"type\":\"response.function_call_arguments.delta\",\"delta\":\"\\\":\\\"\",\"item_id\":\"fc_038668c35ae811d3016a8b2c332090819687d2f367bda0452b\",\"obfuscation\":\"iTTH49MwEj9fT\",\"output_index\":0,\"sequence_number\":5}\n\nevent: response.function_call_arguments.delta\ndata: {\"type\":\"response.function_call_arguments.delta\",\"delta\":\"Paris\",\"item_id\":\"fc_038668c35ae811d3016a8b2c332090819687d2f367bda0452b\",\"obfuscation\":\"a4qZjBh3OWk\",\"output_index\":0,\"sequence_number\":6}\n\nevent: response.function_call_arguments.delta\ndata: {\"type\":\"response.function_call_arguments.delta\",\"delta\":\"\\\"}\",\"item_id\":\"fc_038668c35ae811d3016a8b2c332090819687d2f367bda0452b\",\"obfuscation\":\"6Gj7WmQUxBa5qn\",\"output_index\":0,\"sequence_number\":7}\n\nevent: response.function_call_arguments.done\ndata: {\"type\":\"response.function_call_arguments.done\",\"arguments\":\"{\\\"city\\\":\\\"Paris\\\"}\",\"item_id\":\"fc_038668c35ae811d3016a8b2c332090819687d2f367bda0452b\",\"output_index\":0,\"sequence_number\":8}\n\nevent: response.output_item.done\ndata: {\"type\":\"response.output_item.done\",\"item\":{\"id\":\"fc_038668c35ae811d3016a8b2c332090819687d2f367bda0452b\",\"type\":\"function_call\",\"status\":\"completed\",\"arguments\":\"{\\\"city\\\":\\\"Paris\\\"}\",\"call_id\":\"call_urtlVDzFCdgMMgPqZHCTGmEL\",\"name\":\"lookup_weather\"},\"output_index\":0,\"sequence_number\":9}\n\nevent: response.completed\ndata: {\"type\":\"response.completed\",\"response\":{\"id\":\"resp_038668c35ae811d3016a8b2c3273888196a6e34efef3bd3193\",\"object\":\"response\",\"created_at\":1787505714,\"status\":\"completed\",\"background\":false,\"completed_at\":1787505715,\"content_filters\":[{\"blocked\":false,\"source_type\":\"prompt\",\"content_filter_raw\":[],\"content_filter_results\":{},\"content_filter_offsets\":{\"start_offset\":0,\"end_offset\":91,\"check_offset\":0}}],\"error\":null,\"frequency_penalty\":0.0,\"incomplete_details\":null,\"instructions\":null,\"max_output_tokens\":null,\"max_tool_calls\":null,\"model\":\"gpt-5.6-luna\",\"moderation\":null,\"output\":[{\"id\":\"fc_038668c35ae811d3016a8b2c332090819687d2f367bda0452b\",\"type\":\"function_call\",\"status\":\"completed\",\"arguments\":\"{\\\"city\\\":\\\"Paris\\\"}\",\"call_id\":\"call_urtlVDzFCdgMMgPqZHCTGmEL\",\"name\":\"lookup_weather\"}],\"parallel_tool_calls\":true,\"presence_penalty\":0.0,\"previous_response_id\":null,\"prompt_cache_key\":null,\"prompt_cache_retention\":\"24h\",\"reasoning\":{\"context\":\"all_turns\",\"effort\":\"medium\",\"mode\":\"standard\",\"summary\":\"detailed\"},\"safety_identifier\":null,\"service_tier\":\"default\",\"store\":false,\"temperature\":1.0,\"text\":{\"format\":{\"type\":\"text\"},\"verbosity\":\"medium\"},\"tool_choice\":\"auto\",\"tool_usage\":{\"image_gen\":{\"input_tokens\":0,\"input_tokens_details\":{\"image_tokens\":0,\"text_tokens\":0},\"output_tokens\":0,\"output_tokens_details\":{\"image_tokens\":0,\"text_tokens\":0},\"total_tokens\":0},\"web_search\":{\"num_requests\":0}},\"tools\":[{\"type\":\"function\",\"description\":\"Look up the current weather for a city\",\"name\":\"lookup_weather\",\"output_schema\":null,\"parameters\":{\"type\":\"object\",\"properties\":{\"city\":{\"type\":\"string\"}},\"required\":[\"city\"]},\"strict\":false}],\"top_logprobs\":0,\"top_p\":0.98,\"truncation\":\"disabled\",\"usage\":{\"input_tokens\":58,\"input_tokens_details\":{\"cache_write_tokens\":0,\"cached_tokens\":0},\"output_tokens\":18,\"output_tokens_details\":{\"reasoning_tokens\":0},\"total_tokens\":76},\"user\":null,\"metadata\":{}},\"sequence_number\":10}\n\n"
+      }
+    }
+  ]
+}
diff --git a/packages/ai/test/fixtures/recordings/azure/responses-continues-after-a-tool-result.json b/packages/ai/test/fixtures/recordings/azure/responses-continues-after-a-tool-result.json
new file mode 100644
index 00000000000..b6c05e154c2
--- /dev/null
+++ b/packages/ai/test/fixtures/recordings/azure/responses-continues-after-a-tool-result.json
@@ -0,0 +1,31 @@
+{
+  "version": 1,
+  "metadata": {
+    "tags": [
+      "prefix:azure",
+      "provider:azure"
+    ],
+    "name": "azure/responses-continues-after-a-tool-result",
+    "recordedAt": "2026-08-23T17:21:56.397Z"
+  },
+  "interactions": [
+    {
+      "transport": "http",
+      "request": {
+        "method": "POST",
+        "url": "https://aiden-azury-group.openai.azure.com/openai/v1/responses?api-version=v1",
+        "headers": {
+          "content-type": "application/json"
+        },
+        "body": "{\"model\":\"gpt-5.6-luna\",\"input\":[{\"role\":\"user\",\"content\":[{\"type\":\"input_text\",\"text\":\"What is the weather in Paris?\"}]},{\"type\":\"function_call\",\"call_id\":\"call_paris_1\",\"name\":\"lookup_weather\",\"arguments\":\"{\\\"city\\\":\\\"Paris\\\"}\"},{\"type\":\"function_call_output\",\"call_id\":\"call_paris_1\",\"output\":\"18C, light rain\"}],\"tools\":[{\"type\":\"function\",\"name\":\"lookup_weather\",\"description\":\"Look up the current weather for a city\",\"parameters\":{\"type\":\"object\",\"properties\":{\"city\":{\"type\":\"string\"}},\"required\":[\"city\"]},\"strict\":false}],\"store\":false,\"include\":[\"reasoning.encrypted_content\"],\"reasoning\":{\"effort\":\"medium\",\"summary\":\"auto\"},\"stream\":true}"
+      },
+      "response": {
+        "status": 200,
+        "headers": {
+          "content-type": "text/event-stream; charset=utf-8"
+        },
+        "body": "event: response.created\ndata: {\"type\":\"response.created\",\"response\":{\"id\":\"resp_01b60cb95ad658c9016a8b2c33725c819799bf17e133419dd9\",\"object\":\"response\",\"created_at\":1787505715,\"status\":\"in_progress\",\"background\":false,\"completed_at\":null,\"content_filters\":null,\"error\":null,\"frequency_penalty\":0.0,\"incomplete_details\":null,\"instructions\":null,\"max_output_tokens\":null,\"max_tool_calls\":null,\"model\":\"gpt-5.6-luna\",\"moderation\":null,\"output\":[],\"parallel_tool_calls\":true,\"presence_penalty\":0.0,\"previous_response_id\":null,\"prompt_cache_key\":null,\"prompt_cache_retention\":\"24h\",\"reasoning\":{\"context\":\"all_turns\",\"effort\":\"medium\",\"mode\":\"standard\",\"summary\":\"detailed\"},\"safety_identifier\":null,\"service_tier\":\"auto\",\"store\":false,\"temperature\":1.0,\"text\":{\"format\":{\"type\":\"text\"},\"verbosity\":\"medium\"},\"tool_choice\":\"auto\",\"tool_usage\":{\"image_gen\":{\"input_tokens\":0,\"input_tokens_details\":{\"image_tokens\":0,\"text_tokens\":0},\"output_tokens\":0,\"output_tokens_details\":{\"image_tokens\":0,\"text_tokens\":0},\"total_tokens\":0},\"web_search\":{\"num_requests\":0}},\"tools\":[{\"type\":\"function\",\"description\":\"Look 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+      }
+    }
+  ]
+}
diff --git a/packages/ai/test/fixtures/recordings/azure/responses-streams-text.json b/packages/ai/test/fixtures/recordings/azure/responses-streams-text.json
new file mode 100644
index 00000000000..937227ee4f7
--- /dev/null
+++ b/packages/ai/test/fixtures/recordings/azure/responses-streams-text.json
@@ -0,0 +1,31 @@
+{
+  "version": 1,
+  "metadata": {
+    "tags": [
+      "prefix:azure",
+      "provider:azure"
+    ],
+    "name": "azure/responses-streams-text",
+    "recordedAt": "2026-08-23T17:21:54.158Z"
+  },
+  "interactions": [
+    {
+      "transport": "http",
+      "request": {
+        "method": "POST",
+        "url": "https://aiden-azury-group.openai.azure.com/openai/v1/responses?api-version=v1",
+        "headers": {
+          "content-type": "application/json"
+        },
+        "body": "{\"model\":\"gpt-5.6-luna\",\"input\":[{\"role\":\"user\",\"content\":[{\"type\":\"input_text\",\"text\":\"Reply with exactly one word: bonjour\"}]}],\"store\":false,\"include\":[\"reasoning.encrypted_content\"],\"reasoning\":{\"effort\":\"medium\",\"summary\":\"auto\"},\"stream\":true}"
+      },
+      "response": {
+        "status": 200,
+        "headers": {
+          "content-type": "text/event-stream; charset=utf-8"
+        },
+        "body": "event: response.created\ndata: {\"type\":\"response.created\",\"response\":{\"id\":\"resp_027c7373d7896543016a8b2c3166e08195b8ef40ca578fd90a\",\"object\":\"response\",\"created_at\":1787505713,\"status\":\"in_progress\",\"background\":false,\"completed_at\":null,\"content_filters\":null,\"error\":null,\"frequency_penalty\":0.0,\"incomplete_details\":null,\"instructions\":null,\"max_output_tokens\":null,\"max_tool_calls\":null,\"model\":\"gpt-5.6-luna\",\"moderation\":null,\"output\":[],\"parallel_tool_calls\":true,\"presence_penalty\":0.0,\"previous_response_id\":null,\"prompt_cache_key\":null,\"prompt_cache_retention\":\"24h\",\"reasoning\":{\"context\":\"all_turns\",\"effort\":\"medium\",\"mode\":\"standard\",\"summary\":\"detailed\"},\"safety_identifier\":null,\"service_tier\":\"auto\",\"store\":false,\"temperature\":1.0,\"text\":{\"format\":{\"type\":\"text\"},\"verbosity\":\"medium\"},\"tool_choice\":\"auto\",\"tool_usage\":{\"image_gen\":{\"input_tokens\":0,\"input_tokens_details\":{\"image_tokens\":0,\"text_tokens\":0},\"output_tokens\":0,\"output_tokens_details\":{\"image_tokens\":0,\"text_tokens\":0},\"total_tokens\":0},\"web_search\":{\"num_requests\":0}},\"tools\":[],\"top_logprobs\":0,\"top_p\":0.98,\"truncation\":\"disabled\",\"usage\":null,\"user\":null,\"metadata\":{}},\"sequence_number\":0}\n\nevent: response.in_progress\ndata: 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+      }
+    }
+  ]
+}
diff --git a/packages/ai/test/fixtures/recordings/google-vertex/calls-a-tool.json b/packages/ai/test/fixtures/recordings/google-vertex/calls-a-tool.json
new file mode 100644
index 00000000000..cc91c018bd0
--- /dev/null
+++ b/packages/ai/test/fixtures/recordings/google-vertex/calls-a-tool.json
@@ -0,0 +1,32 @@
+{
+  "version": 1,
+  "metadata": {
+    "tags": [
+      "prefix:google-vertex",
+      "provider:google-vertex",
+      "protocol:gemini"
+    ],
+    "name": "google-vertex/calls-a-tool",
+    "recordedAt": "2026-08-23T17:21:51.036Z"
+  },
+  "interactions": [
+    {
+      "transport": "http",
+      "request": {
+        "method": "POST",
+        "url": "https://aiplatform.googleapis.com/v1/publishers/google/models/gemini-3.5-flash:streamGenerateContent?alt=sse",
+        "headers": {
+          "content-type": "application/json"
+        },
+        "body": "{\"contents\":[{\"role\":\"user\",\"parts\":[{\"text\":\"What is the weather in Paris? Use the lookup_weather tool.\"}]}],\"tools\":[{\"functionDeclarations\":[{\"name\":\"lookup_weather\",\"description\":\"Look up the current weather for a city\",\"parameters\":{\"required\":[\"city\"],\"type\":\"object\",\"properties\":{\"city\":{\"type\":\"string\"}}}}]}]}"
+      },
+      "response": {
+        "status": 200,
+        "headers": {
+          "content-type": "text/event-stream"
+        },
+        "body": "data: {\"candidates\": [{\"content\": {\"role\": \"model\",\"parts\": [{\"functionCall\": {\"name\": \"lookup_weather\",\"args\": {\"city\": \"Paris\"},\"id\": \"call_425130\"},\"thoughtSignature\": \"AY89a1+1fXnLgYhHMuN3Ak6LBhT6PcrYOW7iPav4LfsacvG/Z6l1yJ+AsU7vWhFj/JyPIbsJJQ+GjohM9sCIZ6nqUOIg3reo/7osmrCvFrVHedTHQcwiPzoz2Kp3gb+uWjFAXxk1EX4IRAKcu0ox1W/Z9PpuZvHkTerGO2a82e02N6MAF1YhhtbXFvSdqLRih2Os68rdOk5/Bcld7ol8qUgeyIZ3CtI3OJ5jwRcD8LjvK33A7ZFzH5Bxp/peUmXvqnu5iNhnGBxZaJy/vupCtxRZxjaS+ojG0/UhyrnRiKIpbzQ0FBkxePPn8GCX/LOe2y3GUc98co8lN8OOuCd9ZmEdx5AjHmQkPO9fAV9SxG6Bda6SDWVL8o/Uz3WSQYoUEfAdoajEWIBvcisoeCJjb7zgmRRZ9VQSPl3RXj5LFRvX8jn0YKV1CahYbc24jA==\"}]}}],\"usageMetadata\": {\"trafficType\": \"ON_DEMAND\"},\"modelVersion\": \"gemini-3.5-flash\",\"createTime\": \"2026-08-23T17:21:50.308576Z\",\"responseId\": \"LiyLauDqErCErb8Pj8aWkAs\"}\r\n\r\ndata: {\"candidates\": [{\"content\": {\"role\": \"model\",\"parts\": [{\"text\": \"\"}]},\"finishReason\": \"STOP\"}],\"usageMetadata\": {\"promptTokenCount\": 39,\"candidatesTokenCount\": 16,\"totalTokenCount\": 102,\"trafficType\": \"ON_DEMAND\",\"promptTokensDetails\": [{\"modality\": \"TEXT\",\"tokenCount\": 39}],\"candidatesTokensDetails\": [{\"modality\": \"TEXT\",\"tokenCount\": 16}],\"thoughtsTokenCount\": 47},\"modelVersion\": \"gemini-3.5-flash\",\"createTime\": \"2026-08-23T17:21:50.308576Z\",\"responseId\": \"LiyLauDqErCErb8Pj8aWkAs\"}\r\n\r\n"
+      }
+    }
+  ]
+}
diff --git a/packages/ai/test/fixtures/recordings/google-vertex/continues-after-a-tool-result.json b/packages/ai/test/fixtures/recordings/google-vertex/continues-after-a-tool-result.json
new file mode 100644
index 00000000000..f419d6e5c9f
--- /dev/null
+++ b/packages/ai/test/fixtures/recordings/google-vertex/continues-after-a-tool-result.json
@@ -0,0 +1,32 @@
+{
+  "version": 1,
+  "metadata": {
+    "tags": [
+      "prefix:google-vertex",
+      "provider:google-vertex",
+      "protocol:gemini"
+    ],
+    "name": "google-vertex/continues-after-a-tool-result",
+    "recordedAt": "2026-08-23T17:21:51.853Z"
+  },
+  "interactions": [
+    {
+      "transport": "http",
+      "request": {
+        "method": "POST",
+        "url": "https://aiplatform.googleapis.com/v1/publishers/google/models/gemini-3.5-flash:streamGenerateContent?alt=sse",
+        "headers": {
+          "content-type": "application/json"
+        },
+        "body": "{\"contents\":[{\"role\":\"user\",\"parts\":[{\"text\":\"What is the weather in Paris?\"}]},{\"role\":\"model\",\"parts\":[{\"functionCall\":{\"name\":\"lookup_weather\",\"args\":{\"city\":\"Paris\"}},\"thoughtSignature\":\"skip_thought_signature_validator\"}]},{\"role\":\"user\",\"parts\":[{\"functionResponse\":{\"name\":\"lookup_weather\",\"response\":{\"name\":\"lookup_weather\",\"content\":\"18C, light rain\"}}}]}],\"tools\":[{\"functionDeclarations\":[{\"name\":\"lookup_weather\",\"description\":\"Look up the current weather for a city\",\"parameters\":{\"required\":[\"city\"],\"type\":\"object\",\"properties\":{\"city\":{\"type\":\"string\"}}}}]}]}"
+      },
+      "response": {
+        "status": 200,
+        "headers": {
+          "content-type": "text/event-stream"
+        },
+        "body": "data: {\"candidates\": [{\"content\": {\"role\": \"model\",\"parts\": [{\"text\": \"The weather in Paris is currently 18°C with light rain.\"}]}}],\"usageMetadata\": {\"trafficType\": \"ON_DEMAND\"},\"modelVersion\": \"gemini-3.5-flash\",\"createTime\": \"2026-08-23T17:21:51.220919Z\",\"responseId\": \"LyyLave9DbWnrb8P1IjLmQQ\"}\r\n\r\ndata: {\"candidates\": [{\"content\": {\"role\": \"model\",\"parts\": [{\"text\": \"\",\"thoughtSignature\": \"AY89a197c+fpHJftPtcufnqMAyoRQKVEQK+KeG+RVHVx2wKil3L4jP4YWvfVbcuOFr2jio4Kre/hCrDANAoMFSvaZrdaPeo1b5bXQSmJKMH03yM5M6q6ME6JiBvXym143U4exIde4UbOh2tMeyXMvB3aWxcavIHd78g5G5QPLreo6A3LO5871cYYVeRwteY+/zbEdqfaAq1hlk6WYpWkNljYpjMyKwr15YC8rFLh3HYayS9tTN++GGrk/reZn6C3OEPlzPou/pXRATzcEAGVl/TW\"}]},\"finishReason\": \"STOP\"}],\"usageMetadata\": {\"promptTokenCount\": 59,\"candidatesTokenCount\": 15,\"totalTokenCount\": 98,\"trafficType\": \"ON_DEMAND\",\"promptTokensDetails\": [{\"modality\": \"TEXT\",\"tokenCount\": 59}],\"candidatesTokensDetails\": [{\"modality\": \"TEXT\",\"tokenCount\": 15}],\"thoughtsTokenCount\": 24},\"modelVersion\": \"gemini-3.5-flash\",\"createTime\": \"2026-08-23T17:21:51.220919Z\",\"responseId\": \"LyyLave9DbWnrb8P1IjLmQQ\"}\r\n\r\n"
+      }
+    }
+  ]
+}
diff --git a/packages/ai/test/fixtures/recordings/google-vertex/streams-text.json b/packages/ai/test/fixtures/recordings/google-vertex/streams-text.json
new file mode 100644
index 00000000000..cc95b74191b
--- /dev/null
+++ b/packages/ai/test/fixtures/recordings/google-vertex/streams-text.json
@@ -0,0 +1,32 @@
+{
+  "version": 1,
+  "metadata": {
+    "tags": [
+      "prefix:google-vertex",
+      "provider:google-vertex",
+      "protocol:gemini"
+    ],
+    "name": "google-vertex/streams-text",
+    "recordedAt": "2026-08-23T17:21:50.112Z"
+  },
+  "interactions": [
+    {
+      "transport": "http",
+      "request": {
+        "method": "POST",
+        "url": "https://aiplatform.googleapis.com/v1/publishers/google/models/gemini-3.5-flash:streamGenerateContent?alt=sse",
+        "headers": {
+          "content-type": "application/json"
+        },
+        "body": "{\"contents\":[{\"role\":\"user\",\"parts\":[{\"text\":\"Reply with exactly one word: hello\"}]}]}"
+      },
+      "response": {
+        "status": 200,
+        "headers": {
+          "content-type": "text/event-stream"
+        },
+        "body": "data: {\"candidates\": [{\"content\": {\"role\": \"model\",\"parts\": [{\"text\": \"Hello\"}]}}],\"usageMetadata\": {\"trafficType\": \"ON_DEMAND\"},\"modelVersion\": \"gemini-3.5-flash\",\"createTime\": \"2026-08-23T17:21:48.528714Z\",\"responseId\": \"LCyLasqiIO6crb8P1sDboQc\"}\r\n\r\ndata: {\"candidates\": [{\"content\": {\"role\": \"model\",\"parts\": [{\"text\": \"\",\"thoughtSignature\": \"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\"}]},\"finishReason\": \"STOP\"}],\"usageMetadata\": {\"promptTokenCount\": 7,\"candidatesTokenCount\": 1,\"totalTokenCount\": 150,\"trafficType\": \"ON_DEMAND\",\"promptTokensDetails\": [{\"modality\": \"TEXT\",\"tokenCount\": 7}],\"candidatesTokensDetails\": [{\"modality\": \"TEXT\",\"tokenCount\": 1}],\"thoughtsTokenCount\": 142},\"modelVersion\": \"gemini-3.5-flash\",\"createTime\": \"2026-08-23T17:21:48.528714Z\",\"responseId\": \"LCyLasqiIO6crb8P1sDboQc\"}\r\n\r\n"
+      }
+    }
+  ]
+}
diff --git a/packages/ai/test/provider/azure.recorded.test.ts b/packages/ai/test/provider/azure.recorded.test.ts
new file mode 100644
index 00000000000..51e79f5a5b2
--- /dev/null
+++ b/packages/ai/test/provider/azure.recorded.test.ts
@@ -0,0 +1,93 @@
+import { describe, expect } from "bun:test"
+import { Effect } from "effect"
+import { LLM, Message, ToolDefinition, ToolCallPart } from "../../src/index.js"
+import { Azure } from "../../src/providers.js"
+import { LLMClient } from "../../src/route.js"
+import { recordedTests } from "../recorded-test.js"
+
+const resourceName = process.env.AZURE_OPENAI_RESOURCE_NAME ?? "aiden-azury-group"
+
+const chatModel = Azure.configure({
+  resourceName,
+  apiKey: process.env.AZURE_OPENAI_API_KEY ?? "fixture",
+}).chat("gpt-5.6-luna")
+
+const responsesModel = Azure.configure({
+  resourceName,
+  apiKey: process.env.AZURE_OPENAI_API_KEY ?? "fixture",
+}).responses("gpt-5.6-luna")
+
+const lookupWeather = ToolDefinition.make({
+  name: "lookup_weather",
+  description: "Look up the current weather for a city",
+  inputSchema: { type: "object", properties: { city: { type: "string" } }, required: ["city"] },
+})
+
+const recorded = recordedTests({
+  prefix: "azure",
+  provider: "azure",
+  requires: ["AZURE_OPENAI_API_KEY"],
+})
+
+describe("Azure OpenAI recorded", () => {
+  recorded.effect("chat streams text", () =>
+    Effect.gen(function* () {
+      const response = yield* LLMClient.generate(
+        LLM.request({ model: chatModel, prompt: "Reply with exactly one word: hello" }),
+      )
+
+      expect(response.text.toLowerCase()).toContain("hello")
+    }),
+  )
+
+  recorded.effect("responses streams text", () =>
+    Effect.gen(function* () {
+      const response = yield* LLMClient.generate(
+        LLM.request({ model: responsesModel, prompt: "Reply with exactly one word: bonjour" }),
+      )
+
+      expect(response.text.toLowerCase()).toContain("bonjour")
+    }),
+  )
+
+  recorded.effect("responses calls a tool", () =>
+    Effect.gen(function* () {
+      const response = yield* LLMClient.generate(
+        LLM.request({
+          model: responsesModel,
+          prompt: "What is the weather in Paris? Use the lookup_weather tool.",
+          tools: [lookupWeather],
+        }),
+      )
+
+      const call = response.toolCalls.find((part) => part.name === "lookup_weather")
+      expect(call).toBeDefined()
+      expect(call?.input).toMatchObject({ city: "Paris" })
+    }),
+  )
+
+  recorded.effect("responses continues after a tool result", () =>
+    Effect.gen(function* () {
+      const response = yield* LLMClient.generate(
+        LLM.request({
+          model: responsesModel,
+          messages: [
+            Message.user("What is the weather in Paris?"),
+            Message.assistant([
+              ToolCallPart.make({ id: "call_paris_1", name: "lookup_weather", input: { city: "Paris" } }),
+            ]),
+            Message.tool({
+              id: "call_paris_1",
+              name: "lookup_weather",
+              result: "18C, light rain",
+              resultType: "text",
+            }),
+          ],
+          tools: [lookupWeather],
+        }),
+      )
+
+      expect(response.text.length).toBeGreaterThan(0)
+    }),
+  )
+})
diff --git a/packages/ai/test/provider/gemini.test.ts b/packages/ai/test/provider/gemini.test.ts
index 0c6766822df..dcbc8a79b40 100644
--- a/packages/ai/test/provider/gemini.test.ts
+++ b/packages/ai/test/provider/gemini.test.ts
@@ -156,14 +156,13 @@ describe("Gemini route", () => {
       expect(prepared.body.contents).toEqual([
         {
           role: "model",
-          parts: [{ functionCall: { id: undefined, name: "lookup", args: { query: "weather" } } }],
+          parts: [{ functionCall: { name: "lookup", args: { query: "weather" } } }],
         },
         {
           role: "user",
           parts: [
             {
               functionResponse: {
-                id: undefined,
                 name: "lookup",
                 response: { name: "lookup", content: "done" },
               },
@@ -201,8 +200,8 @@ describe("Gemini route", () => {
         {
           role: "model",
           parts: [
-            { functionCall: { id: undefined, name: "lookup", args: { query: "weather" } } },
-            { functionCall: { id: undefined, name: "lookup", args: { query: "time" } } },
+            { functionCall: { name: "lookup", args: { query: "weather" } } },
+            { functionCall: { name: "lookup", args: { query: "time" } } },
           ],
         },
         {
@@ -210,14 +209,12 @@ describe("Gemini route", () => {
           parts: [
             {
               functionResponse: {
-                id: undefined,
                 name: "lookup",
                 response: { name: "lookup", content: "sunny" },
               },
             },
             {
               functionResponse: {
-                id: undefined,
                 name: "lookup",
                 response: { name: "lookup", content: "noon" },
               },
@@ -228,6 +225,104 @@ describe("Gemini route", () => {
     }),
   )
 
+  it.effect("lowers function call ids for gemini 3 models", () =>
+    Effect.gen(function* () {
+      const prepared = yield* compileRequest(
+        LLM.request({
+          model: gemini3,
+          messages: [
+            Message.assistant([ToolCallPart.make({ id: "call_1", name: "lookup", input: { query: "weather" } })]),
+            Message.tool({ id: "call_1", name: "lookup", result: "done", resultType: "text" }),
+          ],
+        }),
+      )
+
+      expect(prepared.body.contents).toEqual([
+        {
+          role: "model",
+          parts: [
+            {
+              functionCall: { id: "call_1", name: "lookup", args: { query: "weather" } },
+              thoughtSignature: "skip_thought_signature_validator",
+            },
+          ],
+        },
+        {
+          role: "user",
+          parts: [
+            {
+              functionResponse: {
+                id: "call_1",
+                name: "lookup",
+                response: { name: "lookup", content: "done" },
+              },
+            },
+          ],
+        },
+      ])
+    }),
+  )
+
+  it.effect("omits function call ids entirely for pre-gemini-3 models", () =>
+    Effect.gen(function* () {
+      const messages = [
+        Message.assistant([ToolCallPart.make({ id: "call_1", name: "lookup", input: { query: "weather" } })]),
+        Message.tool({ id: "call_1", name: "lookup", result: "done", resultType: "text" }),
+      ]
+      const legacy = yield* compileRequest(LLM.request({ model, messages }))
+      const older = yield* compileRequest(
+        LLM.request({
+          model: Gemini.route
+            .with({
+              endpoint: { baseURL: "https://generativelanguage.test/v1beta/" },
+              auth: Auth.header("x-goog-api-key", "test"),
+            })
+            .model({ id: "gemini-1.5-flash" }),
+          messages,
+        }),
+      )
+
+      expect(legacy.body.contents).toEqual([
+        { role: "model", parts: [{ functionCall: { name: "lookup", args: { query: "weather" } } }] },
+        {
+          role: "user",
+          parts: [{ functionResponse: { name: "lookup", response: { name: "lookup", content: "done" } } }],
+        },
+      ])
+      expect(JSON.stringify(legacy.body.contents)).not.toContain('"id"')
+      expect(JSON.stringify(older.body.contents)).not.toContain('"id"')
+    }),
+  )
+
+  it.effect("includes function call ids for non-gemini model ids", () =>
+    Effect.gen(function* () {
+      const prepared = yield* compileRequest(
+        LLM.request({
+          model: Gemini.route
+            .with({
+              endpoint: { baseURL: "https://generativelanguage.test/v1beta/" },
+              auth: Auth.header("x-goog-api-key", "test"),
+            })
+            .model({ id: "gemma-3-27b-it" }),
+          messages: [
+            Message.assistant([ToolCallPart.make({ id: "call_1", name: "lookup", input: { query: "weather" } })]),
+            Message.tool({ id: "call_1", name: "lookup", result: "done", resultType: "text" }),
+          ],
+        }),
+      )
+
+      expect(prepared.body.contents).toEqual([
+        { role: "model", parts: [{ functionCall: { id: "call_1", name: "lookup", args: { query: "weather" } } }] },
+        {
+          role: "user",
+          parts: [
+            { functionResponse: { id: "call_1", name: "lookup", response: { name: "lookup", content: "done" } } },
+          ],
+        },
+      ])
+    }),
+  )
+
   it.effect("prepares multimodal user input and tool history", () =>
     Effect.gen(function* () {
       const prepared = yield* compileRequest(
@@ -419,13 +514,16 @@ describe("Gemini route", () => {
       expect(prepared.body.contents).toEqual([
         {
           role: "model",
-          parts: [{ functionCall: { name: "read", args: { path: "pixel.png" } }, thoughtSignature: "sig_1" }],
+          parts: [
+            { functionCall: { id: "call_image", name: "read", args: { path: "pixel.png" } }, thoughtSignature: "sig_1" },
+          ],
         },
         {
           role: "user",
           parts: [
             {
               functionResponse: {
+                id: "call_image",
                 name: "read",
                 response: { name: "read", content: "Image read successfully" },
                 parts: [{ inlineData: { mimeType: "image/png", data: "AAECAw==" } }],
@@ -849,7 +947,7 @@ describe("Gemini route", () => {
       })
       expect(toolCall).toMatchObject({
         id: "provider_call",
-        providerMetadata: { google: { functionCallId: "provider_call", thoughtSignature: "tool_sig" } },
+        providerMetadata: { google: { thoughtSignature: "tool_sig" } },
       })
       expect(response.events.findIndex((event) => event.type === "reasoning-end")).toBeLessThan(
         response.events.findIndex((event) => event.type === "tool-call"),
@@ -857,7 +955,7 @@ describe("Gemini route", () => {
 
       const prepared = yield* compileRequest(
         LLM.request({
-          model,
+          model: gemini3,
           messages: [
             Message.assistant([
               { type: "reasoning", text: "thinking", providerMetadata: reasoningEnd?.providerMetadata },
@@ -873,7 +971,6 @@ describe("Gemini route", () => {
               name: "lookup",
               result: "done",
               resultType: "text",
-              providerMetadata: toolCall?.providerMetadata,
             }),
           ],
         }),
@@ -977,7 +1074,7 @@ describe("Gemini route", () => {
           role: "model",
           parts: [
             {
-              functionCall: { id: undefined, name: "lookup", args: { query: "weather" } },
+              functionCall: { id: "tool_0", name: "lookup", args: { query: "weather" } },
               thoughtSignature: "skip_thought_signature_validator",
             },
           ],
@@ -987,7 +1084,7 @@ describe("Gemini route", () => {
           parts: [
             {
               functionResponse: {
-                id: undefined,
+                id: "tool_0",
                 name: "lookup",
                 response: { name: "lookup", content: "done" },
               },
@@ -1023,15 +1120,15 @@ describe("Gemini route", () => {
           role: "model",
           parts: [
             {
-              functionCall: { id: undefined, name: "lookup", args: { query: "weather" } },
+              functionCall: { id: "tool_0", name: "lookup", args: { query: "weather" } },
               thoughtSignature: "parallel_signature",
             },
             {
-              functionCall: { id: undefined, name: "lookup", args: { query: "news" } },
+              functionCall: { id: "tool_1", name: "lookup", args: { query: "news" } },
               thoughtSignature: undefined,
             },
             {
-              functionCall: { id: undefined, name: "lookup", args: { query: "sports" } },
+              functionCall: { id: "tool_2", name: "lookup", args: { query: "sports" } },
               thoughtSignature: undefined,
             },
           ],
@@ -1059,11 +1156,11 @@ describe("Gemini route", () => {
           role: "model",
           parts: [
             {
-              functionCall: { id: undefined, name: "lookup", args: { query: "weather" } },
+              functionCall: { id: "tool_0", name: "lookup", args: { query: "weather" } },
               thoughtSignature: "skip_thought_signature_validator",
             },
             {
-              functionCall: { id: undefined, name: "lookup", args: { query: "news" } },
+              functionCall: { id: "tool_1", name: "lookup", args: { query: "news" } },
               thoughtSignature: "skip_thought_signature_validator",
             },
           ],
@@ -1214,7 +1311,6 @@ describe("Gemini route", () => {
         id: "call_0",
         name: "lookup",
         input: { query: "weather" },
-        providerMetadata: { google: { functionCallId: "call_0" } },
       })
       expect(response.toolCalls[1]).toMatchObject({
         type: "tool-call",
@@ -1230,6 +1326,37 @@ describe("Gemini route", () => {
     }),
   )
 
+  it.effect("replaces repeated supplier ids with fresh fallback ids", () =>
+    Effect.gen(function* () {
+      const body = sseEvents({
+        candidates: [
+          {
+            content: {
+              role: "model",
+              parts: [
+                { functionCall: { id: "dup_call", name: "lookup", args: { query: "weather" } } },
+                { functionCall: { id: "dup_call", name: "lookup", args: { query: "news" } } },
+              ],
+            },
+            finishReason: "STOP",
+          },
+        ],
+      })
+      const response = yield* LLMClient.generate(
+        LLMRequest.update(request, {
+          tools: [ToolDefinition.make({ name: "lookup", description: "Lookup data", inputSchema: { type: "object" } })],
+        }),
+      ).pipe(Effect.provide(fixedResponse(body)))
+
+      expect(response.toolCalls[0]).toMatchObject({
+        id: "dup_call",
+        providerMetadata: undefined,
+      })
+      expect(response.toolCalls[1].id).toMatch(/^tool_[0-9a-zA-Z]+$/)
+      expect(response.toolCalls[1].id).not.toBe(response.toolCalls[0].id)
+    }),
+  )
+
   it.effect("assigns distinct unique fallback ids across separate requests", () =>
     Effect.gen(function* () {
       const body = sseEvents({
diff --git a/packages/ai/test/provider/google-vertex.recorded.test.ts b/packages/ai/test/provider/google-vertex.recorded.test.ts
new file mode 100644
index 00000000000..3fab9bf12b2
--- /dev/null
+++ b/packages/ai/test/provider/google-vertex.recorded.test.ts
@@ -0,0 +1,77 @@
+import { describe, expect } from "bun:test"
+import { Effect } from "effect"
+
+import { LLM, Message, ToolDefinition, ToolCallPart } from "../../src/index.js"
+import { GoogleVertex } from "../../src/providers.js"
+import { LLMClient } from "../../src/route.js"
+import { recordedTests } from "../recorded-test.js"
+
+const model = GoogleVertex.configure({
+  apiKey: process.env.GOOGLE_VERTEX_API_KEY ?? "fixture",
+}).model("gemini-3.5-flash")
+
+const lookupWeather = ToolDefinition.make({
+  name: "lookup_weather",
+  description: "Look up the current weather for a city",
+  inputSchema: { type: "object", properties: { city: { type: "string" } }, required: ["city"] },
+})
+
+const recorded = recordedTests({
+  prefix: "google-vertex",
+  provider: "google-vertex",
+  protocol: "gemini",
+  requires: ["GOOGLE_VERTEX_API_KEY"],
+})
+
+describe("Google Vertex Gemini recorded", () => {
+  recorded.effect("streams text", () =>
+    Effect.gen(function* () {
+      const response = yield* LLMClient.generate(
+        LLM.request({ model, prompt: "Reply with exactly one word: hello" }),
+      )
+
+      expect(response.text.toLowerCase()).toContain("hello")
+    }),
+  )
+
+  recorded.effect("calls a tool", () =>
+    Effect.gen(function* () {
+      const response = yield* LLMClient.generate(
+        LLM.request({
+          model,
+          prompt: "What is the weather in Paris? Use the lookup_weather tool.",
+          tools: [lookupWeather],
+        }),
+      )
+
+      const call = response.toolCalls.find((part) => part.name === "lookup_weather")
+      expect(call).toBeDefined()
+      expect(call?.input).toMatchObject({ city: "Paris" })
+    }),
+  )
+
+  recorded.effect("continues after a tool result", () =>
+    Effect.gen(function* () {
+      const response = yield* LLMClient.generate(
+        LLM.request({
+          model,
+          messages: [
+            Message.user("What is the weather in Paris?"),
+            Message.assistant([
+              ToolCallPart.make({ id: "call_paris_1", name: "lookup_weather", input: { city: "Paris" } }),
+            ]),
+            Message.tool({
+              id: "call_paris_1",
+              name: "lookup_weather",
+              result: "18C, light rain",
+              resultType: "text",
+            }),
+          ],
+          tools: [lookupWeather],
+        }),
+      )
+
+      expect(response.text.length).toBeGreaterThan(0)
+    }),
+  )
+})
diff --git a/packages/ai/test/provider/google-vertex.test.ts b/packages/ai/test/provider/google-vertex.test.ts
index ac9f61cdc99..e7ed8a0b09b 100644
--- a/packages/ai/test/provider/google-vertex.test.ts
+++ b/packages/ai/test/provider/google-vertex.test.ts
@@ -1,7 +1,7 @@
 import { describe, expect } from "bun:test"
 import { Effect } from "effect"
 import { HttpClientRequest } from "effect/unstable/http"
-import { LLM } from "../../src/index.js"
+import { LLM, Message, ToolCallPart } from "../../src/index.js"
 import { GoogleVertex, GoogleVertexChat, GoogleVertexMessages, GoogleVertexResponses } from "../../src/providers.js"
 import { LLMClient } from "../../src/route.js"
 import { compileRequest } from "../../src/route/client.js"
@@ -75,6 +75,53 @@ describe("Google Vertex providers", () => {
     }),
   )
 
+  it.effect("strips function call ids Vertex does not accept from lowered bodies", () =>
+    Effect.gen(function* () {
+      const prepared = yield* compileRequest(
+        LLM.request({
+          model: GoogleVertex.configure({
+            accessToken: "vertex-token",
+            project: "vertex-project",
+          }).model("gemini-3.5-flash"),
+          messages: [
+            Message.assistant([
+              ToolCallPart.make({
+                id: "call_1",
+                name: "lookup",
+                input: { query: "weather" },
+                providerMetadata: { google: { functionCallId: "provider_call_1" } },
+              }),
+            ]),
+            Message.tool({
+              id: "call_1",
+              name: "lookup",
+              result: "sunny",
+              resultType: "text",
+              providerMetadata: { google: { functionCallId: "provider_call_1" } },
+            }),
+          ],
+        }),
+      )
+
+      expect(JSON.stringify(prepared.body.contents)).not.toContain('"id"')
+      expect(prepared.body.contents).toMatchObject([
+        { role: "model", parts: [{ functionCall: { id: undefined, name: "lookup", args: { query: "weather" } } }] },
+        {
+          role: "user",
+          parts: [
+            {
+              functionResponse: {
+                id: undefined,
+                name: "lookup",
+                response: { name: "lookup", content: "sunny" },
+              },
+            },
+          ],
+        },
+      ])
+    }),
+  )
+
   it.effect("projects Anthropic Messages onto the Vertex raw-predict API", () =>
     Effect.gen(function* () {
       const model = GoogleVertexMessages.configure({
diff --git a/packages/ai/test/tool-runtime.test.ts b/packages/ai/test/tool-runtime.test.ts
index 2000c1f99ed..e1af1fc55df 100644
--- a/packages/ai/test/tool-runtime.test.ts
+++ b/packages/ai/test/tool-runtime.test.ts
@@ -191,7 +191,7 @@ describe("LLMClient tools", () => {
         success: Schema.String,
         execute: () => Effect.succeed("hello"),
       })
-      const providerMetadata = { google: { functionCallId: "provider_call" } }
+      const providerMetadata = { google: { thoughtSignature: "provider_sig" } }
       const dispatched = yield* ToolRuntime.dispatch(
         { tool },
         LLMEvent.toolCall({ id: "call_1", name: "tool", input: {}, providerMetadata }),