diff --git a/packages/ai/src/protocols/open-responses.ts b/packages/ai/src/protocols/open-responses.ts
index 92c822682e..3ec5575f89 100644
--- a/packages/ai/src/protocols/open-responses.ts
+++ b/packages/ai/src/protocols/open-responses.ts
@@ -154,6 +154,7 @@ export const coreFields = {
   tools: optionalArray(Tool),
   tool_choice: Schema.optional(ToolChoice),
   store: Schema.optional(Schema.Boolean),
+  truncation: Schema.optional(OpenResponsesOptions.TruncationSchema),
   service_tier: Schema.optional(OpenResponsesOptions.ServiceTierSchema),
   prompt_cache_key: Schema.optional(Schema.String),
   include: optionalArray(OpenResponsesOptions.ResponseIncludableSchema),
@@ -577,6 +578,7 @@ const lowerOptions = (request: LLMRequest) => {
       : {}),
     ...(options.textVerbosity ? { text: { verbosity: options.textVerbosity } } : {}),
     ...(options.serviceTier ? { service_tier: options.serviceTier } : {}),
+    ...(options.truncation ? { truncation: options.truncation } : {}),
   }
 }
 
diff --git a/packages/ai/src/protocols/utils/open-responses-options.ts b/packages/ai/src/protocols/utils/open-responses-options.ts
index 834606817e..ff148fc1fd 100644
--- a/packages/ai/src/protocols/utils/open-responses-options.ts
+++ b/packages/ai/src/protocols/utils/open-responses-options.ts
@@ -16,19 +16,25 @@ export type ResponseIncludable = (typeof ResponseIncludables)[number]
 export const ServiceTiers = ["auto", "default", "flex", "priority"] as const
 export type ServiceTier = (typeof ServiceTiers)[number]
 
+export const Truncations = ["auto", "disabled"] as const
+export type Truncation = (typeof Truncations)[number]
+
 const TEXT_VERBOSITY = new Set<string>(["low", "medium", "high"])
 const INCLUDABLES = new Set<string>(ResponseIncludables)
 const SERVICE_TIERS = new Set<string>(ServiceTiers)
+const TRUNCATIONS = new Set<string>(Truncations)
 
 const isTextVerbosity = (value: unknown): value is Schema.Schema.Type<typeof TextVerbosity> =>
   typeof value === "string" && TEXT_VERBOSITY.has(value)
 
 const isServiceTier = (value: unknown): value is ServiceTier => typeof value === "string" && SERVICE_TIERS.has(value)
+const isTruncation = (value: unknown): value is Truncation => typeof value === "string" && TRUNCATIONS.has(value)
 
 export const ReasoningEffort = Schema.String
 export const TextVerbositySchema = TextVerbosity
 export const ResponseIncludableSchema = Schema.Literals(ResponseIncludables)
 export const ServiceTierSchema = Schema.Literals(ServiceTiers)
+export const TruncationSchema = Schema.Literals(Truncations)
 
 export interface Resolved {
   readonly instructions?: string
@@ -38,6 +44,7 @@ export interface Resolved {
   readonly include?: ReadonlyArray<ResponseIncludable>
   readonly textVerbosity?: Schema.Schema.Type<typeof TextVerbosity>
   readonly serviceTier?: ServiceTier
+  readonly truncation?: Truncation
 }
 
 export const resolve = (request: LLMRequest): Resolved => {
@@ -57,6 +64,7 @@ export const resolve = (request: LLMRequest): Resolved => {
     include: include.length > 0 ? include : undefined,
     textVerbosity: isTextVerbosity(input?.textVerbosity) ? input.textVerbosity : undefined,
     serviceTier: isServiceTier(input?.serviceTier) ? input.serviceTier : undefined,
+    truncation: isTruncation(input?.truncation) ? input.truncation : undefined,
   }
 }
 
diff --git a/packages/ai/src/providers/open-responses-options.ts b/packages/ai/src/providers/open-responses-options.ts
index 7f8cff95d2..1a844e2732 100644
--- a/packages/ai/src/providers/open-responses-options.ts
+++ b/packages/ai/src/providers/open-responses-options.ts
@@ -1,4 +1,4 @@
-import type { ResponseIncludable, ServiceTier } from "../protocols/utils/open-responses-options.js"
+import type { ResponseIncludable, ServiceTier, Truncation } from "../protocols/utils/open-responses-options.js"
 import type { ProviderOptions, ReasoningEffort, TextVerbosity } from "../schema/index.js"
 
 export interface OpenResponsesOptionsInput {
@@ -10,6 +10,7 @@ export interface OpenResponsesOptionsInput {
   readonly include?: ReadonlyArray<ResponseIncludable>
   readonly textVerbosity?: TextVerbosity
   readonly serviceTier?: ServiceTier
+  readonly truncation?: Truncation
 }
 
 export type OpenResponsesProviderOptionsInput = ProviderOptions & {
diff --git a/packages/ai/test/provider/openai-compatible-responses.test.ts b/packages/ai/test/provider/openai-compatible-responses.test.ts
index e5f8024d34..0ca953ee22 100644
--- a/packages/ai/test/provider/openai-compatible-responses.test.ts
+++ b/packages/ai/test/provider/openai-compatible-responses.test.ts
@@ -123,13 +123,14 @@ describe("Open Responses-compatible route", () => {
       const model = configure({
         apiKey: "test-key",
         baseURL: "https://responses.example.test/v1",
-        providerOptions: { openresponses: { reasoningEffort: "low", store: true } },
+        providerOptions: { openresponses: { reasoningEffort: "low", store: true, truncation: "auto" } },
       }).model("example-model")
       const prepared = yield* compileRequest(LLM.request({ model, prompt: "Think." }))
 
       expect(prepared.body).toMatchObject({
         reasoning: { effort: "low" },
         store: true,
+        truncation: "auto",
       })
     }),
   )
diff --git a/packages/ai/test/provider/openai-responses.test.ts b/packages/ai/test/provider/openai-responses.test.ts
index 0cc08c6bd7..dd97982baa 100644
--- a/packages/ai/test/provider/openai-responses.test.ts
+++ b/packages/ai/test/provider/openai-responses.test.ts
@@ -1283,6 +1283,7 @@ describe("OpenAI Responses route", () => {
               reasoningEffort: "high",
               reasoningSummary: "auto",
               include: ["reasoning.encrypted_content"],
+              truncation: "disabled",
             },
           },
         }),
@@ -1293,6 +1294,7 @@ describe("OpenAI Responses route", () => {
       expect(prepared.body.include).toEqual(["reasoning.encrypted_content"])
       expect(prepared.body.reasoning).toEqual({ effort: "high", summary: "auto" })
       expect(prepared.body.text).toEqual({ verbosity: "low" })
+      expect(prepared.body.truncation).toBe("disabled")
     }),
   )