From e3b588e7d2e72fd29f7b28567300d3963df36566 Mon Sep 17 00:00:00 2001
From: Aiden Cline <63023139+rekram1-node@users.noreply.github.com>
Date: Thu, 24 Sep 2026 16:27:30 -0500
Subject: [PATCH] refactor(ai): apply tool schema rules once per request
 (#51162)

---
 packages/ai/AGENTS.md                         |  1 +
 .../ai/src/protocols/anthropic-messages.ts    | 13 +++-------
 packages/ai/src/protocols/bedrock-converse.ts | 16 ++++--------
 packages/ai/src/protocols/gemini.ts           | 13 +++++-----
 packages/ai/src/protocols/meta-responses.ts   |  8 +-----
 packages/ai/src/protocols/mistral-chat.ts     | 13 +++-------
 packages/ai/src/protocols/open-responses.ts   | 12 +++------
 packages/ai/src/protocols/openai-chat.ts      | 20 +++-----------
 packages/ai/src/protocols/openai-responses.ts | 26 +++++--------------
 .../ai/src/protocols/utils/tool-schema.ts     | 24 +++++++++++------
 packages/ai/src/route/client.ts               |  9 +++++--
 packages/ai/src/route/protocol.ts             |  4 ++-
 packages/core/src/aisdk.ts                    |  2 ++
 13 files changed, 60 insertions(+), 101 deletions(-)

diff --git a/packages/ai/AGENTS.md b/packages/ai/AGENTS.md
index 56100667ead..80a77993ab1 100644
--- a/packages/ai/AGENTS.md
+++ b/packages/ai/AGENTS.md
@@ -275,6 +275,7 @@ Use this order for every protocol module:
 ### Rules
 
 - Keep protocol files focused on the protocol. Move provider-specific projection, signing, media normalization, or other bulky transformations into `src/protocols/utils/*`.
+- Send `tool.inputSchema` as given. `prepareRequest` applies the tool schema rules (`ToolSchemaProjection.tools`) once per request, including tools in namespaces. A protocol whose API needs a model family's rules for every model declares `sanitizer` instead of transforming schemas itself.
 - Use `Effect.fn("Provider.fromRequest")` for request body construction entrypoints. Use `Effect.fn(...)` for event handlers that yield effects; keep purely synchronous handlers as plain functions returning a `StepResult` that the dispatcher lifts via `Effect.succeed(...)`.
 - Parser state owns terminal information. The state machine records finish reason, usage, and pending tool calls; emit one terminal `finish` event (or `provider-error`) for each completed response. If a provider splits reason and usage across events, merge them in parser state before flushing.
 - Emit exactly one terminal `finish` event for a completed response, normally after a matching `step-finish`. Use `stream.terminal` to stop reading when the provider has a completion sentinel; use `stream.onHalt` when the final event must be flushed after the framed stream ends.
diff --git a/packages/ai/src/protocols/anthropic-messages.ts b/packages/ai/src/protocols/anthropic-messages.ts
index 7d71e9f1226..33805d8e283 100644
--- a/packages/ai/src/protocols/anthropic-messages.ts
+++ b/packages/ai/src/protocols/anthropic-messages.ts
@@ -18,7 +18,6 @@ import {
   type CacheHint,
   type FinishReasonDetails,
   type FinishReason,
-  type JsonSchema,
   type MediaPart,
   type ProviderMetadata,
   type ProviderOptions,
@@ -31,7 +30,6 @@ import { classifyProviderFailure } from "../provider-error.js"
 import { effortUpdate, resolveEffortUpdates } from "../effort-updates.js"
 import * as Cache from "./utils/cache.js"
 import { Lifecycle } from "./utils/lifecycle.js"
-import { ToolSchemaProjection } from "./utils/tool-schema.js"
 import { ToolStream } from "./utils/tool-stream.js"
 
 const ADAPTER = "anthropic-messages"
@@ -525,10 +523,10 @@ const redactedDataFromMetadata = (metadata: ProviderMetadata | undefined, key: s
   return typeof provider.redactedData === "string" ? provider.redactedData : undefined
 }
 
-const lowerTool = (breakpoints: Cache.Breakpoints, tool: ToolDefinition, inputSchema: JsonSchema): AnthropicTool => ({
+const lowerTool = (breakpoints: Cache.Breakpoints, tool: ToolDefinition): AnthropicTool => ({
   name: tool.name,
   description: tool.description,
-  input_schema: inputSchema,
+  input_schema: tool.inputSchema,
   cache_control: cacheControl(breakpoints, tool.cache),
 })
 
@@ -1049,12 +1047,7 @@ const fromRequest = Effect.fn("AnthropicMessages.fromRequest")(function* (reques
   // over-mark we keep their tool hints and shed the message-tail ones first.
   const breakpoints = Cache.newBreakpoints(ANTHROPIC_BREAKPOINT_CAP)
   const flattened = ProviderShared.flattenToolRequest(updates.request)
-  const tools =
-    flattened.tools.length === 0
-      ? undefined
-      : flattened.tools.map((tool) =>
-          lowerTool(breakpoints, tool, ToolSchemaProjection.modelCompatibility(tool.inputSchema, request.model)),
-        )
+  const tools = flattened.tools.length === 0 ? undefined : flattened.tools.map((tool) => lowerTool(breakpoints, tool))
   // Anthropic rejects tool_choice when tools are absent; "none" is only meaningful with tools present.
   const toolChoice = tools === undefined || !request.toolChoice ? undefined : yield* lowerToolChoice(request.toolChoice)
   const systemParts = request.system.filter((part) => part.text.length > 0)
diff --git a/packages/ai/src/protocols/bedrock-converse.ts b/packages/ai/src/protocols/bedrock-converse.ts
index 5d7815ca718..60325a0936d 100644
--- a/packages/ai/src/protocols/bedrock-converse.ts
+++ b/packages/ai/src/protocols/bedrock-converse.ts
@@ -9,7 +9,6 @@ import {
   type CacheHint,
   type FinishReason,
   type FinishReasonDetails,
-  type JsonSchema,
   type LLMRequest,
   type LanguageModel,
   type ProviderMetadata,
@@ -26,7 +25,6 @@ import { BedrockCache } from "./utils/bedrock-cache.js"
 import { BedrockMedia } from "./utils/bedrock-media.js"
 import { Lifecycle } from "./utils/lifecycle.js"
 import { MistralToolID } from "./utils/mistral-tool-id.js"
-import { ToolSchemaProjection } from "./utils/tool-schema.js"
 import { ToolStream } from "./utils/tool-stream.js"
 import { concatBytes } from "../utils/bytes.js"
 
@@ -221,22 +219,18 @@ type BedrockEvent = Schema.Schema.Type<typeof BedrockEvent>
 // =============================================================================
 // Request Lowering
 // =============================================================================
-const lowerToolSpec = (tool: ToolDefinition, inputSchema: JsonSchema): BedrockToolSpec => ({
+const lowerToolSpec = (tool: ToolDefinition): BedrockToolSpec => ({
   toolSpec: {
     name: tool.name,
     ...(tool.description.trim().length > 0 ? { description: tool.description } : {}),
-    inputSchema: { json: inputSchema },
+    inputSchema: { json: tool.inputSchema },
   },
 })
 
-const lowerTools = (
-  model: LanguageModel,
-  breakpoints: BedrockCache.Breakpoints,
-  tools: ReadonlyArray<ToolDefinition>,
-): BedrockTool[] => {
+const lowerTools = (breakpoints: BedrockCache.Breakpoints, tools: ReadonlyArray<ToolDefinition>): BedrockTool[] => {
   const result: BedrockTool[] = []
   for (const tool of tools) {
-    result.push(lowerToolSpec(tool, ToolSchemaProjection.modelCompatibility(tool.inputSchema, model)))
+    result.push(lowerToolSpec(tool))
     const cachePoint = BedrockCache.block(breakpoints, tool.cache)
     if (cachePoint) result.push(cachePoint)
   }
@@ -473,7 +467,7 @@ const fromRequest = Effect.fn("BedrockConverse.fromRequest")(function* (request:
   const toolConfig = (() => {
     if (flattened.tools.length === 0) return undefined
     return {
-      tools: lowerTools(request.model, breakpoints, flattened.tools),
+      tools: lowerTools(breakpoints, flattened.tools),
       // Converse has no native "none". Keep definitions stable for prompt
       // caching and omit only the unsupported choice.
       toolChoice,
diff --git a/packages/ai/src/protocols/gemini.ts b/packages/ai/src/protocols/gemini.ts
index 0cc74a702a6..1d8e502dbb6 100644
--- a/packages/ai/src/protocols/gemini.ts
+++ b/packages/ai/src/protocols/gemini.ts
@@ -11,7 +11,6 @@ import {
   Usage,
   type FinishReason,
   type LLMRequest,
-  type LanguageModel,
   type MediaPart,
   type ProviderMetadata,
   type ProviderOptions,
@@ -24,7 +23,6 @@ import { Media } from "../media.js"
 import { JsonObject, knownString, lenient, optionalArray, optionalNull, ProviderShared } from "./shared.js"
 import { GeminiGenerateContent } from "./utils/gemini-generate-content.js"
 import { Lifecycle } from "./utils/lifecycle.js"
-import { ToolSchemaProjection } from "./utils/tool-schema.js"
 
 const ADAPTER = "gemini"
 // Google documents this sentinel for replaying Gemini 3 function calls after their original signature was lost.
@@ -270,12 +268,11 @@ interface ParserState {
 // =============================================================================
 // Request Lowering
 // =============================================================================
-// Tool schemas go in `parametersJsonSchema`, which accepts standard JSON Schema. Gemini's schema
-// rules are this API's default, including for tuned endpoints whose IDs do not name Gemini.
-const lowerTool = (tool: ToolDefinition, model: LanguageModel) => ({
+// Tool schemas go in `parametersJsonSchema`, which accepts standard JSON Schema.
+const lowerTool = (tool: ToolDefinition) => ({
   name: tool.name,
   description: tool.description,
-  parametersJsonSchema: ToolSchemaProjection.modelCompatibility(tool.inputSchema, model, "gemini"),
+  parametersJsonSchema: tool.inputSchema,
 })
 
 const lowerToolConfig = (toolChoice: NonNullable<LLMRequest["toolChoice"]>) =>
@@ -482,7 +479,7 @@ const fromRequest = Effect.fn("Gemini.fromRequest")(function* (request: LLMReque
     tools: hasTools
       ? [
           {
-            functionDeclarations: flattened.tools.map((tool) => lowerTool(tool, request.model)),
+            functionDeclarations: flattened.tools.map(lowerTool),
           },
         ]
       : undefined,
@@ -818,6 +815,8 @@ export const protocol = Protocol.make({
     schema: GeminiBody,
     from: fromRequest,
   },
+  // Gemini's schema rules are this API's default, including for tuned endpoints whose IDs do not name Gemini.
+  sanitizer: "gemini",
   stream: {
     event: Protocol.jsonEvent(GeminiEvent),
     initial: (request) => ({
diff --git a/packages/ai/src/protocols/meta-responses.ts b/packages/ai/src/protocols/meta-responses.ts
index 3bcf9a95d67..79827fa3178 100644
--- a/packages/ai/src/protocols/meta-responses.ts
+++ b/packages/ai/src/protocols/meta-responses.ts
@@ -5,7 +5,6 @@ import { LLMEvent, LLMRequest, Message, ToolResultPart } from "../schema/index.j
 import { OpenResponses } from "./open-responses.js"
 import { JsonObject, optionalArray, optionalNull, ProviderShared } from "./shared.js"
 import { ResponsesHostedTools } from "./utils/responses-hosted-tools.js"
-import { ToolSchemaProjection } from "./utils/tool-schema.js"
 import { detectMediaType } from "../utils/media-type.js"
 
 const ADAPTER = "meta-responses"
@@ -103,12 +102,7 @@ const fromRequest = Effect.fn("MetaResponses.fromRequest")(function* (request: L
         ? undefined
         : yield* Effect.forEach(projected.tools, (tool) =>
             Effect.gen(function* () {
-              if (tool.native === undefined)
-                return yield* OpenResponses.lowerTool(
-                  NAME,
-                  tool,
-                  ToolSchemaProjection.modelCompatibility(tool.inputSchema, request.model),
-                )
+              if (tool.native === undefined) return yield* OpenResponses.lowerTool(NAME, tool)
               return yield* ProviderShared.validateWith(Schema.decodeUnknownEffect(NativeTool))(tool.native.meta)
             }),
           ),
diff --git a/packages/ai/src/protocols/mistral-chat.ts b/packages/ai/src/protocols/mistral-chat.ts
index 8f00e6b1f29..b1b1720f204 100644
--- a/packages/ai/src/protocols/mistral-chat.ts
+++ b/packages/ai/src/protocols/mistral-chat.ts
@@ -13,7 +13,6 @@ import {
   UnknownProviderError,
   Usage,
   type FinishReasonDetails,
-  type JsonSchema,
   type LLMRequest,
   type MediaPart,
   type ToolCallPart,
@@ -23,7 +22,6 @@ import { classifyProviderFailure } from "../provider-error.js"
 import { JsonObject, optionalArray, optionalNull, ProviderShared } from "./shared.js"
 import { Lifecycle } from "./utils/lifecycle.js"
 import { MistralToolID } from "./utils/mistral-tool-id.js"
-import { ToolSchemaProjection } from "./utils/tool-schema.js"
 import { ToolStream } from "./utils/tool-stream.js"
 
 const ADAPTER = "mistral-chat"
@@ -368,9 +366,9 @@ const lowerMessages = Effect.fn("MistralChat.lowerMessages")(function* (request:
   return messages
 })
 
-const lowerTool = (tool: ToolDefinition, inputSchema: JsonSchema): MistralTool => ({
+const lowerTool = (tool: ToolDefinition): MistralTool => ({
   type: "function",
-  function: { name: tool.name, description: tool.description, parameters: inputSchema, strict: false },
+  function: { name: tool.name, description: tool.description, parameters: tool.inputSchema, strict: false },
 })
 
 export const fromRequest = Effect.fn("MistralChat.fromRequest")(function* (request: LLMRequest) {
@@ -396,12 +394,7 @@ export const fromRequest = Effect.fn("MistralChat.fromRequest")(function* (reque
   return {
     model: request.model.id,
     messages: yield* lowerMessages(flattened.request),
-    tools:
-      flattened.tools.length > 0
-        ? flattened.tools.map((tool) =>
-            lowerTool(tool, ToolSchemaProjection.modelCompatibility(tool.inputSchema, request.model)),
-          )
-        : undefined,
+    tools: flattened.tools.length > 0 ? flattened.tools.map(lowerTool) : undefined,
     tool_choice: toolChoice,
     stream: true as const,
     max_tokens: request.generation?.maxTokens,
diff --git a/packages/ai/src/protocols/open-responses.ts b/packages/ai/src/protocols/open-responses.ts
index f42f03022b8..2d56648067c 100644
--- a/packages/ai/src/protocols/open-responses.ts
+++ b/packages/ai/src/protocols/open-responses.ts
@@ -8,7 +8,6 @@ import {
   ProviderInternalError,
   Usage,
   type FinishReason,
-  type JsonSchema,
   type LLMRequest,
   type MediaPart,
   type ProviderMetadata,
@@ -24,7 +23,6 @@ import { classifyProviderFailure } from "../provider-error.js"
 import { effortUpdate } from "../effort-updates.js"
 import { OpenResponsesOptions } from "./utils/open-responses-options.js"
 import { Lifecycle } from "./utils/lifecycle.js"
-import { ToolSchemaProjection } from "./utils/tool-schema.js"
 import { ToolStream } from "./utils/tool-stream.js"
 
 const ADAPTER = "open-responses"
@@ -443,18 +441,14 @@ interface ReasoningStreamItem {
 // =============================================================================
 // Request Lowering
 // =============================================================================
-export const lowerTool = Effect.fn("OpenResponses.lowerTool")(function* (
-  protocolName: string,
-  tool: ToolDefinition,
-  inputSchema: JsonSchema,
-) {
+export const lowerTool = Effect.fn("OpenResponses.lowerTool")(function* (protocolName: string, tool: ToolDefinition) {
   if (tool.native !== undefined)
     return yield* ProviderShared.invalidRequest(`${protocolName} does not support provider-native tool ${tool.name}`)
   return {
     type: "function" as const,
     name: tool.name,
     description: tool.description,
-    parameters: inputSchema,
+    parameters: tool.inputSchema,
     // The common tool definition does not currently express Responses strict-schema policy.
     strict: false,
   }
@@ -827,7 +821,7 @@ export const fromRequestWithAdapter = Effect.fn("OpenResponses.fromRequestWithAd
         : yield* Effect.forEach(projected.tools, (tool) =>
             tool.native !== undefined && adapter.nativeTool
               ? adapter.nativeTool(tool.native)
-              : lowerTool(adapter.name, tool, ToolSchemaProjection.modelCompatibility(tool.inputSchema, request.model)),
+              : lowerTool(adapter.name, tool),
           ),
     tool_choice:
       allowedToolChoice(request) ??
diff --git a/packages/ai/src/protocols/openai-chat.ts b/packages/ai/src/protocols/openai-chat.ts
index 3d4b06a3c97..b72864abbcb 100644
--- a/packages/ai/src/protocols/openai-chat.ts
+++ b/packages/ai/src/protocols/openai-chat.ts
@@ -17,7 +17,6 @@ import {
   type FinishReason,
   type FinishReasonDetails,
   type CacheHint,
-  type JsonSchema,
   type LLMRequest,
   type MediaPart,
   type ReasoningPart,
@@ -29,7 +28,6 @@ import { classifyProviderFailure } from "../provider-error.js"
 import { isRecord, JsonObject, optionalArray, optionalNull, ProviderShared } from "./shared.js"
 import { OpenAIOptions } from "./utils/openai-options.js"
 import { Lifecycle } from "./utils/lifecycle.js"
-import { ToolSchemaProjection } from "./utils/tool-schema.js"
 import { ToolStream } from "./utils/tool-stream.js"
 
 const ADAPTER = "openai-chat"
@@ -330,17 +328,12 @@ interface LoweringOptions {
   readonly toolCallID?: (id: string) => string
 }
 
-const lowerTool = (
-  tool: ToolDefinition,
-  inputSchema: JsonSchema,
-  options: LoweringOptions,
-  supportsStrictMode: boolean,
-): OpenAIChatTool => ({
+const lowerTool = (tool: ToolDefinition, options: LoweringOptions, supportsStrictMode: boolean): OpenAIChatTool => ({
   type: "function",
   function: {
     name: tool.name,
     description: tool.description,
-    parameters: inputSchema,
+    parameters: tool.inputSchema,
     ...(supportsStrictMode ? { strict: false } : {}),
   },
   cache_control: options.cacheControl?.(tool.cache),
@@ -825,14 +818,7 @@ export const fromRequest = Effect.fn("OpenAIChat.fromRequest")(function* (
         ? hasHistory
           ? []
           : undefined
-        : flattened.tools.map((tool) =>
-            lowerTool(
-              tool,
-              ToolSchemaProjection.modelCompatibility(tool.inputSchema, request.model),
-              options,
-              supportsStrictMode,
-            ),
-          ),
+        : flattened.tools.map((tool) => lowerTool(tool, options, supportsStrictMode)),
     tool_choice: hasActiveTools && request.toolChoice ? yield* lowerToolChoice(request.toolChoice) : undefined,
     stream: true as const,
     ...(supportsUsageInStreaming ? { stream_options: { include_usage: true } } : {}),
diff --git a/packages/ai/src/protocols/openai-responses.ts b/packages/ai/src/protocols/openai-responses.ts
index 840cbaf8fe0..13f32d1e9d8 100644
--- a/packages/ai/src/protocols/openai-responses.ts
+++ b/packages/ai/src/protocols/openai-responses.ts
@@ -5,20 +5,12 @@ import { Auth } from "../route/auth.js"
 import { Endpoint } from "../route/endpoint.js"
 import { Protocol } from "../route/protocol.js"
 import { HttpTransport } from "../route/transport/index.js"
-import {
-  LLMRequest,
-  mergeJsonRecords,
-  type JsonSchema,
-  type LanguageModel,
-  type ToolDefinition,
-  type ToolEntry,
-} from "../schema/index.js"
+import { LLMRequest, mergeJsonRecords, type ToolDefinition, type ToolEntry } from "../schema/index.js"
 import { resolveEffortUpdates } from "../effort-updates.js"
 import { OpenResponses } from "./open-responses.js"
 import { OpenResponsesOptions } from "./utils/open-responses-options.js"
 import { JsonObject, optionalArray, optionalNull, ProviderShared } from "./shared.js"
 import { ResponsesHostedTools } from "./utils/responses-hosted-tools.js"
-import { ToolSchemaProjection } from "./utils/tool-schema.js"
 import { OpenResponsesChannel } from "./open-responses-channel.js"
 import { ResponsesCompaction } from "./utils/responses-compaction.js"
 import { ResponsesCheckpoint } from "./utils/responses-checkpoint.js"
@@ -174,20 +166,19 @@ const nativeImageTool = (tool: ToolDefinition) => {
   return Schema.is(OpenAIResponsesImageGenerationTool)(native) ? native : undefined
 }
 
-const lowerTool = Effect.fn("OpenAIResponses.lowerTool")(function* (tool: ToolDefinition, inputSchema: JsonSchema) {
+const lowerTool = Effect.fn("OpenAIResponses.lowerTool")(function* (tool: ToolDefinition) {
   const native = nativeImageToolInput(tool)
   if (native !== undefined) {
     if (Schema.is(OpenAIResponsesImageGenerationTool)(native)) return native
     return yield* ProviderShared.invalidRequest("OpenAI Responses image generation tool options are invalid")
   }
-  return yield* OpenResponses.lowerTool(NAME, tool, inputSchema)
+  return yield* OpenResponses.lowerTool(NAME, tool)
 })
 
 // Native namespaces hold only function tools, so deeper levels flatten into
 // the leaf names the same way non-native protocols flatten the whole tree.
-const lowerToolEntry = Effect.fn("OpenAIResponses.lowerToolEntry")(function* (tool: ToolEntry, model: LanguageModel) {
-  if (tool.type === "tool")
-    return yield* lowerTool(tool, ToolSchemaProjection.modelCompatibility(tool.inputSchema, model))
+const lowerToolEntry = Effect.fn("OpenAIResponses.lowerToolEntry")(function* (tool: ToolEntry) {
+  if (tool.type === "tool") return yield* lowerTool(tool)
   // OpenAI requires a namespace description; fall back to a generic one so a
   // missing description never blocks the request.
   return {
@@ -195,7 +186,7 @@ const lowerToolEntry = Effect.fn("OpenAIResponses.lowerToolEntry")(function* (to
     name: tool.name,
     description: tool.description ?? `Tools in the ${tool.name} namespace.`,
     tools: yield* Effect.forEach(ProviderShared.flattenTools(tool.tools), (leaf) =>
-      OpenResponses.lowerTool(NAME, leaf, ToolSchemaProjection.modelCompatibility(leaf.inputSchema, model)),
+      OpenResponses.lowerTool(NAME, leaf),
     ),
   }
 })
@@ -223,10 +214,7 @@ const fromRequest = Effect.fn("OpenAIResponses.fromRequest")(function* (request:
     ...(yield* OpenResponses.lowerConversation(updates.request, adapter)),
     ...OpenResponses.lowerGeneration(request, { ...options, reasoningEffort: updates.effort }),
     context_management: management?.map((edit) => ({ type: edit.type, compact_threshold: edit.compactThreshold })),
-    tools:
-      request.tools.length === 0
-        ? undefined
-        : yield* Effect.forEach(request.tools, (tool) => lowerToolEntry(tool, request.model)),
+    tools: request.tools.length === 0 ? undefined : yield* Effect.forEach(request.tools, lowerToolEntry),
     tool_choice:
       request.tools.length === 0
         ? undefined
diff --git a/packages/ai/src/protocols/utils/tool-schema.ts b/packages/ai/src/protocols/utils/tool-schema.ts
index 100b082b5cb..013cd4d321a 100644
--- a/packages/ai/src/protocols/utils/tool-schema.ts
+++ b/packages/ai/src/protocols/utils/tool-schema.ts
@@ -1,4 +1,4 @@
-import type { JsonSchema, LanguageModel, LanguageModelSanitizerCompatibility } from "../../schema/index.js"
+import { ToolDefinition, type JsonSchema, type LanguageModel, type LLMRequest } from "../../schema/index.js"
 import { isRecord } from "../../utils/record.js"
 import { GeminiJsonSchema } from "./gemini-json-schema.js"
 
@@ -70,13 +70,13 @@ const objectRoot = (schema: JsonSchema): JsonSchema => {
 // Otherwise the protocol's own default applies (the Gemini API always uses Gemini's rules), then the
 // model name selects the family's rules so models reached through gateways and OpenAI-compatible
 // endpoints get the same handling.
-const modelCompatibility = (
-  schema: JsonSchema,
-  model: LanguageModel,
-  protocolDefault?: LanguageModelSanitizerCompatibility,
-): JsonSchema => {
+const modelCompatibility = (schema: JsonSchema, model: LanguageModel): JsonSchema => {
   const root = objectRoot(schema)
-  switch (model.compatibility?.sanitizer ?? protocolDefault ?? MODEL_NAMES.find(([name]) => name.test(model.id))?.[1]) {
+  switch (
+    model.compatibility?.sanitizer ??
+    model.route.sanitizer ??
+    MODEL_NAMES.find(([name]) => name.test(model.id))?.[1]
+  ) {
     case "gemini":
       return gemini(root)
     case "moonshot":
@@ -87,10 +87,18 @@ const modelCompatibility = (
   }
 }
 
+// Applied once to every request before any protocol builds its body, including tools in namespaces.
+const tools = (entries: LLMRequest["tools"], model: LanguageModel): LLMRequest["tools"] =>
+  entries.map((tool) =>
+    tool.type === "tool"
+      ? new ToolDefinition({ ...tool, inputSchema: modelCompatibility(tool.inputSchema, model) })
+      : { ...tool, tools: tools(tool.tools, model) },
+  )
+
 export const ToolSchemaProjection = {
   gemini,
-  modelCompatibility,
   moonshot,
   openAI,
   responses,
+  tools,
 } as const
diff --git a/packages/ai/src/route/client.ts b/packages/ai/src/route/client.ts
index 64e96573b89..83e762160a1 100644
--- a/packages/ai/src/route/client.ts
+++ b/packages/ai/src/route/client.ts
@@ -11,7 +11,8 @@ import { applyEffortUpdates } from "../effort-updates.js"
 import { normalizeToolHistory } from "../tool-history.js"
 import { sanitizeSurrogates } from "../utils/sanitize.js"
 import * as ProviderShared from "../protocols/shared.js"
-import type { ProtocolID, ProviderOptions } from "../schema/index.js"
+import { ToolSchemaProjection } from "../protocols/utils/tool-schema.js"
+import type { LanguageModelSanitizerCompatibility, ProtocolID, ProviderOptions } from "../schema/index.js"
 import {
   AIError,
   CompactionResponse,
@@ -57,6 +58,7 @@ export interface Route<
   readonly defaults: RouteDefaults
   readonly body: RouteBody<Body>
   readonly supportsEffortUpdates?: (request: LLMRequest) => boolean
+  readonly sanitizer?: LanguageModelSanitizerCompatibility
   readonly with: {
     <Next extends CompactionOperations | undefined>(
       patch: RoutePatch<Body, Prepared> & { readonly compact: Next },
@@ -388,6 +390,7 @@ function makeFromTransport<Body, Prepared, Frame, Event, State>(
       defaults: routeInput.defaults ?? {},
       body: protocol.body,
       supportsEffortUpdates: protocol.supportsEffortUpdates,
+      sanitizer: protocol.sanitizer,
       with: (patch: RoutePatch<Body, Prepared>) => {
         const { compact, id, provider, providerMetadataKey, auth, transport, endpoint, ...defaults } = patch
         return build({
@@ -559,7 +562,9 @@ const prepareRequest = (request: LLMRequest) => {
       tool.type === "tool" ? tool : { ...tool, tools: dedupe(tool.tools) },
     )
   const resolved = applyCachePolicy(
-    applyEffortUpdates(LLMRequest.update(sanitized, { tools: dedupe(sanitized.tools) })),
+    applyEffortUpdates(
+      LLMRequest.update(sanitized, { tools: ToolSchemaProjection.tools(dedupe(sanitized.tools), sanitized.model) }),
+    ),
   )
   const headers = resolved.model.route.headers?.({ request: resolved })
   return headers === undefined
diff --git a/packages/ai/src/route/protocol.ts b/packages/ai/src/route/protocol.ts
index 329c96923e6..89c8d536108 100644
--- a/packages/ai/src/route/protocol.ts
+++ b/packages/ai/src/route/protocol.ts
@@ -1,5 +1,5 @@
 import { Schema, type Effect } from "effect"
-import type { AIError, LLMEvent, LLMRequest, ProtocolID } from "../schema/index.js"
+import type { AIError, LanguageModelSanitizerCompatibility, LLMEvent, LLMRequest, ProtocolID } from "../schema/index.js"
 
 /**
  * The semantic API contract of one model server family.
@@ -43,6 +43,8 @@ export interface Protocol<Body, Frame, Event, State> {
   readonly stream: ProtocolStream<Frame, Event, State>
   /** Whether `body.from` lowers `Message.effort(...)` markers; wrappers around another `body.from` must forward it. */
   readonly supportsEffortUpdates?: (request: LLMRequest) => boolean
+  /** Tool schema sanitizer for every model on this protocol unless the model's compatibility sets one; wrappers around another `body.from` must forward it. */
+  readonly sanitizer?: LanguageModelSanitizerCompatibility
 }
 
 export interface ProtocolBody<Body> {
diff --git a/packages/core/src/aisdk.ts b/packages/core/src/aisdk.ts
index 175781b9c66..cb27a55584c 100644
--- a/packages/core/src/aisdk.ts
+++ b/packages/core/src/aisdk.ts
@@ -366,6 +366,8 @@ function modelFromLanguage(info: RuntimeInfo, language: LanguageModelV3) {
     provider: ProviderID.make(providerID),
     providerMetadataKey: optionKey,
     protocol: "ai-sdk",
+    // AI SDK providers convert tool schemas themselves, so model-family sanitizers stay off here.
+    sanitizer: "none",
     endpoint: Endpoint.path("/", { baseURL: "https://ai-sdk.local" }),
     auth: Auth.none,
     transport: {