diff --git a/src/backend/controllers/puterai/PuterAIController.shapes.test.ts b/src/backend/controllers/puterai/PuterAIController.shapes.test.ts
index 77631e7f9..42c7b1849 100644
--- a/src/backend/controllers/puterai/PuterAIController.shapes.test.ts
+++ b/src/backend/controllers/puterai/PuterAIController.shapes.test.ts
@@ -201,6 +201,7 @@ describe('PuterAIController.openaiResponses parameter forwarding', () => {
                     context_management: [{ type: 'compaction' }],
                     prompt_cache_key: 'ck',
                     prompt_cache_retention: '24h',
+                    prompt_cache_options: { ttl: '12h', prewarm: true },
                     store: true,
                     truncation: 'auto',
                     service_tier: 'default',
@@ -226,6 +227,9 @@ describe('PuterAIController.openaiResponses parameter forwarding', () => {
             context_management: [{ type: 'compaction' }],
             prompt_cache_key: 'ck',
             prompt_cache_retention: '24h',
+            // Forwarded as sent; the provider keeps only the fields it
+            // accepts.
+            prompt_cache_options: { ttl: '12h', prewarm: true },
             // forced false regardless of the client's request.
             store: false,
             truncation: 'auto',
@@ -639,6 +643,33 @@ describe('PuterAIController.openaiResponses output items', () => {
 // -- /openai/v1/chat/completions edges -------------------------------
 
 describe('PuterAIController.openaiChatCompletions translation edges', () => {
+    it('forwards the prompt-cache fields to the driver', async () => {
+        const completeSpy = stubChatComplete({
+            message: { role: 'assistant', content: 'ok' },
+        });
+
+        const { res } = makeRes();
+        await controller.openaiChatCompletions(
+            makeReq({
+                body: {
+                    model: 'gpt-test',
+                    messages: [{ role: 'user', content: 'hi' }],
+                    prompt_cache_key: 'ck',
+                    prompt_cache_retention: 'in_memory',
+                    prompt_cache_options: { ttl: '30m' },
+                },
+            }),
+            res,
+        );
+
+        const args = completeSpy.mock.calls[0]![0] as Record<string, unknown>;
+        expect(args).toMatchObject({
+            prompt_cache_key: 'ck',
+            prompt_cache_retention: 'in_memory',
+            prompt_cache_options: { ttl: '30m' },
+        });
+    });
+
     it('derives tool_calls from tool_use content blocks when the message has none', async () => {
         stubChatComplete({
             message: {
diff --git a/src/backend/controllers/puterai/PuterAIController.ts b/src/backend/controllers/puterai/PuterAIController.ts
index 02c27bb31..3ea11b39a 100644
--- a/src/backend/controllers/puterai/PuterAIController.ts
+++ b/src/backend/controllers/puterai/PuterAIController.ts
@@ -447,6 +447,7 @@ export class PuterAIController extends PuterController {
                           body.reasoning_effort as ICompleteArguments['reasoning_effort'],
                   }
                 : {}),
+            ...promptCacheArgsFromBody(body),
             ...openaiCompatProvider(body),
             ...(body.fallback === false ? { fallback: false } : {}),
         };
@@ -842,15 +843,7 @@ export class PuterAIController extends PuterController {
                           body.compaction as ICompleteArguments['compaction'],
                   }
                 : {}),
-            ...(body.prompt_cache_key
-                ? { prompt_cache_key: String(body.prompt_cache_key) }
-                : {}),
-            ...(body.prompt_cache_retention
-                ? {
-                      prompt_cache_retention:
-                          body.prompt_cache_retention as ICompleteArguments['prompt_cache_retention'],
-                  }
-                : {}),
+            ...promptCacheArgsFromBody(body),
             // forced off regardless of what the caller sent — OpenAI
             // defaults `store` to true, which would persist state server-side
             // on OpenAI's end that this route gives no way to retrieve.
@@ -1343,6 +1336,33 @@ const openaiCompatProvider = (
     return { provider: DEFAULTS.openaiChat };
 };
 
+/**
+ * The prompt-cache fields both OpenAI-shaped routes forward as sent; the
+ * provider checks the values.
+ */
+const promptCacheArgsFromBody = (
+    body: Record<string, unknown>,
+): Pick<
+    ICompleteArguments,
+    'prompt_cache_key' | 'prompt_cache_retention' | 'prompt_cache_options'
+> => ({
+    ...(body.prompt_cache_key
+        ? { prompt_cache_key: String(body.prompt_cache_key) }
+        : {}),
+    ...(body.prompt_cache_retention
+        ? {
+              prompt_cache_retention:
+                  body.prompt_cache_retention as ICompleteArguments['prompt_cache_retention'],
+          }
+        : {}),
+    ...(body.prompt_cache_options
+        ? {
+              prompt_cache_options:
+                  body.prompt_cache_options as ICompleteArguments['prompt_cache_options'],
+          }
+        : {}),
+});
+
 const randomId = (): string => crypto.randomUUID().replace(/-/g, '');
 const generateId = (prefix: string): string => `${prefix}_${randomId()}`;
 
diff --git a/src/backend/drivers/ai-chat/providers/azure/AzureResponsesProvider.test.ts b/src/backend/drivers/ai-chat/providers/azure/AzureResponsesProvider.test.ts
index 2d1d249ab..2b5164743 100644
--- a/src/backend/drivers/ai-chat/providers/azure/AzureResponsesProvider.test.ts
+++ b/src/backend/drivers/ai-chat/providers/azure/AzureResponsesProvider.test.ts
@@ -449,6 +449,22 @@ describe('AzureResponsesProvider.complete request shape', () => {
         expect(args.service_tier).toBe('default');
     });
 
+    it('sends the wire spelling of the in-memory cache retention', async () => {
+        const provider = makeProvider();
+        responsesCreateMock.mockResolvedValueOnce(okResponse);
+
+        await withTestActor(() =>
+            provider.complete({
+                model: 'gpt-5.3-codex',
+                messages: [{ role: 'user', content: 'hi' }],
+                prompt_cache_retention: 'in-memory',
+            } as never),
+        );
+
+        const [args] = responsesCreateMock.mock.calls[0]!;
+        expect(args.prompt_cache_retention).toBe('in_memory');
+    });
+
     it.each([
         ['previous_response_id', 'resp_1'],
         ['conversation', 'conv_1'],
diff --git a/src/backend/drivers/ai-chat/providers/azure/AzureResponsesProvider.ts b/src/backend/drivers/ai-chat/providers/azure/AzureResponsesProvider.ts
index 9152b691e..e98720737 100644
--- a/src/backend/drivers/ai-chat/providers/azure/AzureResponsesProvider.ts
+++ b/src/backend/drivers/ai-chat/providers/azure/AzureResponsesProvider.ts
@@ -35,6 +35,7 @@ import * as OpenAiUtil from '../../utils/OpenAIUtil.js';
 import {
     clampReasoningEffort,
     openAICompatParams,
+    promptCacheRetentionToWire,
     rejectStatefulResponsesFields,
 } from '../../utils/openaiParams.js';
 import { buildCostsOverride } from '../../utils/pricing.js';
@@ -209,6 +210,9 @@ export class AzureResponsesProvider implements IChatProvider {
         const userIdentifier = upstreamUserIdentifier(actor);
         // Cache key defaults to the actor identifier; see upstreamUserIdentifier.
         const cacheKey = prompt_cache_key ?? userIdentifier;
+        const cacheRetention = promptCacheRetentionToWire(
+            prompt_cache_retention,
+        );
 
         // Resolve any `puter_path` content parts into inline base64 data URLs
         // before the Responses API sees them.
@@ -307,8 +311,8 @@ export class AzureResponsesProvider implements IChatProvider {
             ...(instructions !== undefined ? { instructions } : {}),
             ...(metadata !== undefined ? { metadata } : {}),
             ...(cacheKey !== undefined ? { prompt_cache_key: cacheKey } : {}),
-            ...(prompt_cache_retention !== undefined
-                ? { prompt_cache_retention }
+            ...(cacheRetention !== undefined
+                ? { prompt_cache_retention: cacheRetention }
                 : {}),
             ...(store !== undefined ? { store } : {}),
             ...(max_tokens !== undefined
diff --git a/src/backend/drivers/ai-chat/providers/meta/MetaProvider.ts b/src/backend/drivers/ai-chat/providers/meta/MetaProvider.ts
index c0ca50e02..f3e94615f 100644
--- a/src/backend/drivers/ai-chat/providers/meta/MetaProvider.ts
+++ b/src/backend/drivers/ai-chat/providers/meta/MetaProvider.ts
@@ -23,6 +23,7 @@ import { HttpError } from '../../../../core/http/HttpError.js';
 import type { MeteringService } from '../../../../services/metering/MeteringService.js';
 import { upstreamUserIdentifier } from '../../../util/upstreamIdentifier.js';
 import type { IChatModel, ICompleteArguments } from '../../types.js';
+import { promptCacheRetentionToWire } from '../../utils/openaiParams.js';
 import { sdkClientOptions } from '../../utils/sdkClient.js';
 import {
     type ChatProviderConfig,
@@ -107,12 +108,9 @@ export class MetaProvider extends OpenAICompatProvider {
                 ? requestedEffort
                 : undefined;
 
-        // Puter spells the in-memory retention with a hyphen; Meta's enum
-        // uses an underscore.
-        const cacheRetention =
-            args.prompt_cache_retention === 'in-memory'
-                ? 'in_memory'
-                : args.prompt_cache_retention;
+        const cacheRetention = promptCacheRetentionToWire(
+            args.prompt_cache_retention,
+        );
 
         // The identifier is Puter's abuse attribution, so `custom` can't
         // override it. Cache key defaults to it; see upstreamUserIdentifier.
diff --git a/src/backend/drivers/ai-chat/providers/openai/OpenAiChatCompletionsProvider.test.ts b/src/backend/drivers/ai-chat/providers/openai/OpenAiChatCompletionsProvider.test.ts
index 56a7c02bc..4aa943a4b 100644
--- a/src/backend/drivers/ai-chat/providers/openai/OpenAiChatCompletionsProvider.test.ts
+++ b/src/backend/drivers/ai-chat/providers/openai/OpenAiChatCompletionsProvider.test.ts
@@ -249,6 +249,44 @@ describe('OpenAiChatProvider.complete argument validation', () => {
         expect(result).toEqual({ delegated: true });
     });
 
+    it('delegates a 12h cache lifetime to the Responses provider, which is the only API that writes it', async () => {
+        const { provider } = makeProvider();
+        const sibling = {
+            complete: vi.fn().mockResolvedValue({ delegated: true }),
+        };
+        provider.setResponsesProvider(
+            sibling as unknown as Parameters<
+                typeof provider.setResponsesProvider
+            >[0],
+        );
+
+        const params = {
+            model: 'gpt-6-luna',
+            messages: [{ role: 'user', content: 'hi' }],
+            prompt_cache_options: { ttl: '12h' as const },
+        };
+        const result = await withTestActor(() => provider.complete(params));
+
+        expect(createMock).not.toHaveBeenCalled();
+        expect(sibling.complete).toHaveBeenCalledWith(params);
+        expect(result).toEqual({ delegated: true });
+    });
+
+    it('throws 400 for a 12h cache lifetime without a Responses sibling provider', async () => {
+        const { provider } = makeProvider();
+
+        await expect(
+            withTestActor(() =>
+                provider.complete({
+                    model: 'gpt-6-luna',
+                    messages: [{ role: 'user', content: 'hi' }],
+                    prompt_cache_options: { ttl: '12h' },
+                }),
+            ),
+        ).rejects.toMatchObject({ statusCode: 400 });
+        expect(createMock).not.toHaveBeenCalled();
+    });
+
     it('requestPricing delegates to the Responses sibling (web_search\'s own hold), and no-ops without one', async () => {
         const { provider } = makeProvider();
         const args = {
@@ -349,6 +387,31 @@ describe('OpenAiChatProvider.complete request shape', () => {
         expect(args.safety_identifier).toBe('puter-u42');
     });
 
+    it('forwards 30m prompt_cache_options and the wire spelling of prompt_cache_retention', async () => {
+        const { provider } = makeProvider();
+        createMock.mockResolvedValueOnce(baseCompletion);
+
+        await withTestActor(() =>
+            provider.complete({
+                model: 'gpt-6-luna',
+                messages: [{ role: 'user', content: 'hello' }],
+                prompt_cache_retention: 'in-memory',
+                prompt_cache_options: {
+                    mode: 'explicit',
+                    ttl: '30m',
+                    prewarm: true,
+                } as never,
+            }),
+        );
+
+        const [args] = createMock.mock.calls[0]!;
+        expect(args.prompt_cache_retention).toBe('in_memory');
+        expect(args.prompt_cache_options).toEqual({
+            mode: 'explicit',
+            ttl: '30m',
+        });
+    });
+
     it.each([
         'gpt-6-astra',
         'gpt-6.1-sol',
@@ -665,7 +728,7 @@ describe('OpenAiChatProvider.complete non-stream output', () => {
             },
         });
 
-        await withTestActor(() =>
+        const result = await withTestActor(() =>
             provider.complete({
                 model: 'gpt-6-luna',
                 messages: [{ role: 'user', content: 'hi' }],
@@ -685,6 +748,13 @@ describe('OpenAiChatProvider.complete non-stream output', () => {
             cached_tokens: 1000 * Number(luna.costs.cached_tokens),
             cache_write_tokens: 3000 * Number(luna.costs.cache_write_tokens),
         });
+        // Chat Completions only writes OpenAI's default 30m entries.
+        expect((result as { usageDetails: unknown }).usageDetails).toEqual({
+            inputTokens: 1000,
+            outputTokens: 12,
+            cacheReadTokens: 1000,
+            cacheWrite30mTokens: 3000,
+        });
     });
 
     it('zeroes cached_tokens when prompt_tokens_details is missing', async () => {
diff --git a/src/backend/drivers/ai-chat/providers/openai/OpenAiChatCompletionsProvider.ts b/src/backend/drivers/ai-chat/providers/openai/OpenAiChatCompletionsProvider.ts
index 92e05e4e5..553712fcd 100644
--- a/src/backend/drivers/ai-chat/providers/openai/OpenAiChatCompletionsProvider.ts
+++ b/src/backend/drivers/ai-chat/providers/openai/OpenAiChatCompletionsProvider.ts
@@ -36,6 +36,8 @@ import * as OpenAiUtil from '../../utils/OpenAIUtil.js';
 import {
     clampReasoningEffort,
     openAICompatParams,
+    promptCacheOptionsToWire,
+    promptCacheRetentionToWire,
 } from '../../utils/openaiParams.js';
 import { OPEN_AI_MODELS } from './models.js';
 import type { OpenAiResponsesChatProvider } from './OpenAiChatResponsesProvider.js';
@@ -126,8 +128,11 @@ export class OpenAiChatProvider implements IChatProvider {
             temperature,
             text,
             prompt_cache_key,
+            prompt_cache_retention,
+            prompt_cache_options,
         } = params;
         let { messages, model } = params;
+        const cacheOptions = promptCacheOptionsToWire(prompt_cache_options);
         if (
             tools?.filter((e) => isWebSearchTool(e as Record<string, unknown>))
                 .length
@@ -157,6 +162,18 @@ export class OpenAiChatProvider implements IChatProvider {
             }
             return await this.#responsesProvider.complete(params);
         }
+        // Only the Responses API writes 12h cache entries; Chat Completions
+        // rejects the lifetime.
+        if (cacheOptions?.ttl === '12h') {
+            if (!this.#responsesProvider) {
+                throw new HttpError(
+                    400,
+                    'a 12h prompt cache lifetime requires the OpenAI Responses provider, which is not configured',
+                    { legacyCode: 'bad_request' },
+                );
+            }
+            return await this.#responsesProvider.complete(params);
+        }
         // Validate messages
         if (!Array.isArray(messages)) {
             throw new HttpError(400, '`messages` must be an array', {
@@ -180,6 +197,9 @@ export class OpenAiChatProvider implements IChatProvider {
         const userIdentifier = upstreamUserIdentifier(actor);
         // Cache key defaults to the actor identifier; see upstreamUserIdentifier.
         const cacheKey = prompt_cache_key ?? userIdentifier;
+        const cacheRetention = promptCacheRetentionToWire(
+            prompt_cache_retention,
+        );
 
         // Strip Anthropic-only shape a fallback-replayed message can carry
         // (thinking/server-tool blocks, cache_control, citations) before the
@@ -216,6 +236,12 @@ export class OpenAiChatProvider implements IChatProvider {
             user: userIdentifier,
             safety_identifier: userIdentifier,
             ...(cacheKey !== undefined ? { prompt_cache_key: cacheKey } : {}),
+            ...(cacheRetention !== undefined
+                ? { prompt_cache_retention: cacheRetention }
+                : {}),
+            ...(cacheOptions !== undefined
+                ? { prompt_cache_options: cacheOptions }
+                : {}),
             messages: messages,
             model: modelUsed.id,
             ...(mappedTools?.length ? { tools: mappedTools } : {}),
@@ -254,28 +280,11 @@ export class OpenAiChatProvider implements IChatProvider {
         );
 
         return OpenAiUtil.handle_completion_output({
-            usage_calculator: ({ usage, setUsageCosts }) => {
-                const cachedTokens =
-                    usage.prompt_tokens_details?.cached_tokens ?? 0;
-                // GPT-5.6 and later bill cache writes at 1.25x input. They're
-                // reported inside `prompt_tokens`, like cached reads.
-                // The SDK doesn't type `cache_write_tokens` yet.
-                const cacheWriteTokens =
-                    (
-                        usage.prompt_tokens_details as
-                            { cache_write_tokens?: number } | undefined
-                    )?.cache_write_tokens ?? 0;
-                const trackedUsage = {
-                    prompt_tokens:
-                        (usage.prompt_tokens ?? 0) -
-                        cachedTokens -
-                        cacheWriteTokens,
-                    completion_tokens: usage.completion_tokens ?? 0,
-                    cached_tokens: cachedTokens,
-                    ...(cacheWriteTokens
-                        ? { cache_write_tokens: cacheWriteTokens }
-                        : {}),
-                };
+            usage_calculator: ({ usage, setUsageCosts, setUsageDetails }) => {
+                // GPT-5.6 and later report cache writes inside
+                // `prompt_tokens`, like cached reads; Chat Completions only
+                // writes the default 30m entries, billed at 1.25x input.
+                const trackedUsage = OpenAiUtil.splitCachedPrompt(usage);
 
                 const metered = meterChatUsage(
                     this.#meteringService,
@@ -285,6 +294,11 @@ export class OpenAiChatProvider implements IChatProvider {
                     trackedUsage,
                 );
                 setUsageCosts(metered.costs);
+                setUsageDetails(
+                    OpenAiUtil.usageDetailsFromTrackedUsage(metered.usage, {
+                        writeTtl: '30m',
+                    })!,
+                );
                 return metered.usage;
             },
             stream,
diff --git a/src/backend/drivers/ai-chat/providers/openai/OpenAiChatResponsesProvider.test.ts b/src/backend/drivers/ai-chat/providers/openai/OpenAiChatResponsesProvider.test.ts
index 509e6ec4d..7ce8889fa 100644
--- a/src/backend/drivers/ai-chat/providers/openai/OpenAiChatResponsesProvider.test.ts
+++ b/src/backend/drivers/ai-chat/providers/openai/OpenAiChatResponsesProvider.test.ts
@@ -246,6 +246,7 @@ describe('OpenAiResponsesChatProvider model catalog', () => {
                     prompt_tokens: input,
                     cached_tokens: cached,
                     cache_write_tokens: input * 1.25,
+                    cache_write_12h_tokens: input * 2.5,
                     completion_tokens: output,
                 },
                 context: 1_050_000,
@@ -844,7 +845,7 @@ describe('OpenAiResponsesChatProvider.complete non-stream output', () => {
             },
         });
 
-        await withTestActor(() =>
+        const result = await withTestActor(() =>
             provider.complete({
                 model: 'gpt-6-luna',
                 messages: [{ role: 'user', content: 'hi' }],
@@ -867,6 +868,115 @@ describe('OpenAiResponsesChatProvider.complete non-stream output', () => {
             cached_tokens: 1000 * Number(luna.costs.cached_tokens),
             cache_write_tokens: 3000 * Number(luna.costs.cache_write_tokens),
         });
+        // Writes without a per-lifetime breakdown are OpenAI's default 30m
+        // entries, and the neutral breakdown says so.
+        expect((result as { usageDetails: unknown }).usageDetails).toEqual({
+            inputTokens: 1000,
+            outputTokens: 20,
+            cacheReadTokens: 1000,
+            cacheWrite30mTokens: 3000,
+        });
+    });
+
+    it('bills 12h cache writes at 2.5x input and the other writes at 1.25x', async () => {
+        const luna = OPEN_AI_MODELS.find((m) => m.id === 'gpt-6-luna')!;
+        const { provider } = makeProvider();
+        // One request can write both lifetimes: an explicit 12h breakpoint
+        // plus the implicit 30m one OpenAI adds at the end of the prompt.
+        responsesCreateMock.mockResolvedValueOnce({
+            output: [{ role: 'assistant' }],
+            output_text: 'ok',
+            usage: {
+                input_tokens: 6026,
+                output_tokens: 5,
+                input_tokens_details: {
+                    cached_tokens: 0,
+                    cache_write_tokens: 6023,
+                    cache_write_tokens_details: {
+                        ttl_12h_tokens: 6012,
+                        ttl_30m_tokens: 11,
+                    },
+                },
+            },
+        });
+
+        const result = await withTestActor(() =>
+            provider.complete({
+                model: 'gpt-6-luna',
+                messages: [{ role: 'user', content: 'hi' }],
+                prompt_cache_options: { ttl: '12h' },
+            }),
+        );
+
+        const [usage, , , overrides] = recordSpy.mock.calls[0]!;
+        expect(usage).toEqual({
+            prompt_tokens: 3,
+            completion_tokens: 5,
+            cached_tokens: 0,
+            cache_write_tokens: 11,
+            cache_write_12h_tokens: 6012,
+        });
+        expect(luna.costs.cache_write_12h_tokens).toBe(
+            Number(luna.costs.prompt_tokens) * 2.5,
+        );
+        expect(overrides).toEqual({
+            prompt_tokens: 3 * Number(luna.costs.prompt_tokens),
+            completion_tokens: 5 * Number(luna.costs.completion_tokens),
+            cached_tokens: 0,
+            cache_write_tokens: 11 * Number(luna.costs.cache_write_tokens),
+            cache_write_12h_tokens:
+                6012 * Number(luna.costs.cache_write_12h_tokens),
+        });
+        expect((result as { usageDetails: unknown }).usageDetails).toEqual({
+            inputTokens: 3,
+            outputTokens: 5,
+            cacheWrite30mTokens: 11,
+            cacheWrite12hTokens: 6012,
+        });
+    });
+
+    it('forwards prompt_cache_options and the wire spelling of prompt_cache_retention', async () => {
+        const { provider } = makeProvider();
+        responsesCreateMock.mockResolvedValueOnce({
+            output: [{ role: 'assistant' }],
+            output_text: 'ok',
+            usage: { input_tokens: 1, output_tokens: 1 },
+        });
+
+        await withTestActor(() =>
+            provider.complete({
+                model: 'gpt-6-luna',
+                messages: [{ role: 'user', content: 'hi' }],
+                prompt_cache_retention: 'in-memory',
+                prompt_cache_options: {
+                    mode: 'explicit',
+                    ttl: '12h',
+                    comparison_response_id: 'resp_1',
+                } as never,
+            }),
+        );
+
+        const [args] = responsesCreateMock.mock.calls[0]!;
+        expect(args.prompt_cache_retention).toBe('in_memory');
+        expect(args.prompt_cache_options).toEqual({
+            mode: 'explicit',
+            ttl: '12h',
+        });
+    });
+
+    it('rejects a cache lifetime OpenAI does not offer before calling upstream', async () => {
+        const { provider } = makeProvider();
+
+        await expect(
+            withTestActor(() =>
+                provider.complete({
+                    model: 'gpt-6-luna',
+                    messages: [{ role: 'user', content: 'hi' }],
+                    prompt_cache_options: { ttl: '2h' } as never,
+                }),
+            ),
+        ).rejects.toMatchObject({ statusCode: 400 });
+        expect(responsesCreateMock).not.toHaveBeenCalled();
     });
 
     it.each([
@@ -1068,6 +1178,69 @@ describe('OpenAiResponsesChatProvider.complete streaming', () => {
         });
     });
 
+    it('labels streamed cache writes by lifetime on the final usage chunk', async () => {
+        const luna = OPEN_AI_MODELS.find((m) => m.id === 'gpt-6-luna')!;
+        const { provider } = makeProvider();
+        responsesCreateMock.mockReturnValueOnce(
+            asAsyncIterable([
+                { type: 'response.output_text.delta', delta: 'ok' },
+                {
+                    type: 'response.completed',
+                    response: {
+                        usage: {
+                            input_tokens: 6026,
+                            output_tokens: 5,
+                            input_tokens_details: {
+                                cached_tokens: 0,
+                                cache_write_tokens: 6023,
+                                cache_write_tokens_details: {
+                                    ttl_12h_tokens: 6012,
+                                    ttl_30m_tokens: 11,
+                                },
+                            },
+                        },
+                    },
+                },
+            ]),
+        );
+
+        const result = await withTestActor(() =>
+            provider.complete({
+                model: 'gpt-6-luna',
+                messages: [{ role: 'user', content: 'say ok' }],
+                stream: true,
+                prompt_cache_options: { ttl: '12h' },
+            }),
+        );
+        const harness = makeCapturingChatStream();
+        await (
+            result as {
+                init_chat_stream: (p: { chatStream: unknown }) => Promise<void>;
+            }
+        ).init_chat_stream({ chatStream: harness.chatStream });
+
+        const usageEvent = harness.events().find((e) => e.type === 'usage');
+        expect(usageEvent?.usage).toEqual({
+            prompt_tokens: 3,
+            completion_tokens: 5,
+            cached_tokens: 0,
+            cache_write_tokens: 11,
+            cache_write_12h_tokens: 6012,
+        });
+        expect(usageEvent?.usageDetails).toEqual({
+            inputTokens: 3,
+            outputTokens: 5,
+            cacheWrite30mTokens: 11,
+            cacheWrite12hTokens: 6012,
+        });
+        const [, , , overrides] = recordSpy.mock.calls[0]!;
+        expect(overrides).toMatchObject({
+            cache_write_tokens: 11 * Number(luna.costs.cache_write_tokens),
+            cache_write_12h_tokens:
+                6012 * Number(luna.costs.cache_write_12h_tokens),
+        });
+    });
+
     it('emits a tool_use block when response.output_item.done arrives with a function_call', async () => {
         const { provider } = makeProvider();
         responsesCreateMock.mockReturnValueOnce(
diff --git a/src/backend/drivers/ai-chat/providers/openai/OpenAiChatResponsesProvider.ts b/src/backend/drivers/ai-chat/providers/openai/OpenAiChatResponsesProvider.ts
index 0f1deee10..79e5352dd 100644
--- a/src/backend/drivers/ai-chat/providers/openai/OpenAiChatResponsesProvider.ts
+++ b/src/backend/drivers/ai-chat/providers/openai/OpenAiChatResponsesProvider.ts
@@ -32,6 +32,8 @@ import * as OpenAiUtil from '../../utils/OpenAIUtil.js';
 import {
     clampReasoningEffort,
     openAICompatParams,
+    promptCacheOptionsToWire,
+    promptCacheRetentionToWire,
     rejectStatefulResponsesFields,
 } from '../../utils/openaiParams.js';
 import { responseSamplingParams } from '../../utils/responseSampling.js';
@@ -150,6 +152,7 @@ export class OpenAiResponsesChatProvider implements IChatProvider {
         prompt,
         prompt_cache_key,
         prompt_cache_retention,
+        prompt_cache_options,
         store,
         top_p,
         truncation,
@@ -195,6 +198,10 @@ export class OpenAiResponsesChatProvider implements IChatProvider {
         const userIdentifier = upstreamUserIdentifier(actor);
         // Cache key defaults to the actor identifier; see upstreamUserIdentifier.
         const cacheKey = prompt_cache_key ?? userIdentifier;
+        const cacheRetention = promptCacheRetentionToWire(
+            prompt_cache_retention,
+        );
+        const cacheOptions = promptCacheOptionsToWire(prompt_cache_options);
 
         if (tools) {
             // Unravel tools to OpenAI Responses API format
@@ -288,8 +295,11 @@ export class OpenAiResponsesChatProvider implements IChatProvider {
             ...(instructions !== undefined ? { instructions } : {}),
             ...(metadata !== undefined ? { metadata } : {}),
             ...(cacheKey !== undefined ? { prompt_cache_key: cacheKey } : {}),
-            ...(prompt_cache_retention !== undefined
-                ? { prompt_cache_retention }
+            ...(cacheRetention !== undefined
+                ? { prompt_cache_retention: cacheRetention }
+                : {}),
+            ...(cacheOptions !== undefined
+                ? { prompt_cache_options: cacheOptions }
                 : {}),
             ...(store !== undefined ? { store } : {}),
             ...(max_tokens !== undefined
@@ -310,24 +320,17 @@ export class OpenAiResponsesChatProvider implements IChatProvider {
             { signal: Context.get('upstreamSignal') },
         );
         return OpenAiUtil.handle_completion_output_responses_api({
-            usage_calculator: ({ usage, webSearchCalls, setUsageCosts }) => {
-                const cachedTokens =
-                    (usage as any).input_tokens_details?.cached_tokens ?? 0;
-                // GPT-5.6 and later bill cache writes at 1.25x input. They're
-                // reported inside `input_tokens`, like cached reads.
-                const cacheWriteTokens =
-                    (usage as any).input_tokens_details?.cache_write_tokens ??
-                    0;
+            usage_calculator: ({
+                usage,
+                webSearchCalls,
+                setUsageCosts,
+                setUsageDetails,
+            }) => {
+                // GPT-5.6 and later report cache writes inside `input_tokens`,
+                // like cached reads, split by lifetime (30m and 12h entries
+                // cost 1.25x and 2.5x input to write).
                 const trackedUsage: Record<string, number> = {
-                    prompt_tokens:
-                        ((usage as any).input_tokens ?? 0) -
-                        cachedTokens -
-                        cacheWriteTokens,
-                    completion_tokens: (usage as any).output_tokens ?? 0,
-                    cached_tokens: cachedTokens,
-                    ...(cacheWriteTokens
-                        ? { cache_write_tokens: cacheWriteTokens }
-                        : {}),
+                    ...OpenAiUtil.splitCachedPrompt(usage),
                     ...(webSearchCalls
                         ? { web_search_calls: webSearchCalls }
                         : {}),
@@ -356,6 +359,11 @@ export class OpenAiResponsesChatProvider implements IChatProvider {
                         : {},
                 );
                 setUsageCosts?.(metered.costs);
+                setUsageDetails?.(
+                    OpenAiUtil.usageDetailsFromTrackedUsage(metered.usage, {
+                        writeTtl: '30m',
+                    })!,
+                );
                 return metered.usage;
             },
             stream,
diff --git a/src/backend/drivers/ai-chat/providers/openai/models.ts b/src/backend/drivers/ai-chat/providers/openai/models.ts
index 241e26418..378480b9e 100644
--- a/src/backend/drivers/ai-chat/providers/openai/models.ts
+++ b/src/backend/drivers/ai-chat/providers/openai/models.ts
@@ -23,6 +23,8 @@ import type { IChatModel } from '../../types.js';
 
 // Prompts over 272K input tokens are billed at 2x input (cached reads and
 // cache writes included) and 1.5x output for the full request.
+// GPT-5.6 and later bill cache writes by the lifetime requested: 1.25x input
+// for the default 30m entries, 2.5x for 12h entries.
 const GPT_LONG_CONTEXT_PRICING = {
     threshold: 272_000,
     input_multiplier: 2,
@@ -49,6 +51,7 @@ export const OPEN_AI_MODELS: IChatModel[] = [
             prompt_tokens: 100,
             cached_tokens: 5,
             cache_write_tokens: 100 * 1.25,
+            cache_write_12h_tokens: 100 * 2.5,
             completion_tokens: 500,
         },
         long_context_pricing: GPT_LONG_CONTEXT_PRICING,
@@ -74,6 +77,7 @@ export const OPEN_AI_MODELS: IChatModel[] = [
             prompt_tokens: 200,
             cached_tokens: 10,
             cache_write_tokens: 200 * 1.25,
+            cache_write_12h_tokens: 200 * 2.5,
             completion_tokens: 1000,
         },
         long_context_pricing: GPT_LONG_CONTEXT_PRICING,
@@ -99,6 +103,7 @@ export const OPEN_AI_MODELS: IChatModel[] = [
             prompt_tokens: 200,
             cached_tokens: 20,
             cache_write_tokens: 200 * 1.25,
+            cache_write_12h_tokens: 200 * 2.5,
             completion_tokens: 1000,
         },
         long_context_pricing: GPT_LONG_CONTEXT_PRICING,
@@ -124,6 +129,7 @@ export const OPEN_AI_MODELS: IChatModel[] = [
             prompt_tokens: 10,
             cached_tokens: 1,
             cache_write_tokens: 10 * 1.25,
+            cache_write_12h_tokens: 10 * 2.5,
             completion_tokens: 50,
         },
         long_context_pricing: GPT_LONG_CONTEXT_PRICING,
@@ -149,6 +155,7 @@ export const OPEN_AI_MODELS: IChatModel[] = [
             prompt_tokens: 1000,
             cached_tokens: 100,
             cache_write_tokens: 1000 * 1.25,
+            cache_write_12h_tokens: 1000 * 2.5,
             completion_tokens: 5000,
         },
         long_context_pricing: GPT_LONG_CONTEXT_PRICING,
@@ -174,6 +181,7 @@ export const OPEN_AI_MODELS: IChatModel[] = [
             prompt_tokens: 400,
             cached_tokens: 40,
             cache_write_tokens: 400 * 1.25,
+            cache_write_12h_tokens: 400 * 2.5,
             completion_tokens: 2000,
         },
         long_context_pricing: GPT_LONG_CONTEXT_PRICING,
@@ -198,6 +206,7 @@ export const OPEN_AI_MODELS: IChatModel[] = [
             prompt_tokens: 200,
             cached_tokens: 20,
             cache_write_tokens: 200 * 1.25,
+            cache_write_12h_tokens: 200 * 2.5,
             completion_tokens: 1200,
         },
         long_context_pricing: GPT_LONG_CONTEXT_PRICING,
@@ -222,6 +231,7 @@ export const OPEN_AI_MODELS: IChatModel[] = [
             prompt_tokens: 20,
             cached_tokens: 2,
             cache_write_tokens: 20 * 1.25,
+            cache_write_12h_tokens: 20 * 2.5,
             completion_tokens: 120,
         },
         long_context_pricing: GPT_LONG_CONTEXT_PRICING,
diff --git a/src/backend/drivers/ai-chat/types.ts b/src/backend/drivers/ai-chat/types.ts
index 3208e47de..bd59eee28 100644
--- a/src/backend/drivers/ai-chat/types.ts
+++ b/src/backend/drivers/ai-chat/types.ts
@@ -145,13 +145,19 @@ export type StopReason =
     | 'model_context_window_exceeded'
     | (string & {});
 
-/** Provider-neutral usage breakdown. `inputTokens` excludes cache reads/writes. */
+/**
+ * Provider-neutral usage breakdown. `inputTokens` excludes cache reads/writes.
+ * Cache writes are keyed by the lifetime the entry was written with: Claude and
+ * Moonshot write 5m and 1h entries, OpenAI writes 30m and 12h entries.
+ */
 export interface UsageDetails {
     inputTokens: number;
     outputTokens: number; // includes reasoning
     cacheReadTokens?: number;
     cacheWrite5mTokens?: number;
+    cacheWrite30mTokens?: number;
     cacheWrite1hTokens?: number;
+    cacheWrite12hTokens?: number;
     reasoningTokens?: number;
     webSearchRequests?: number;
     webFetchRequests?: number;
@@ -168,10 +174,22 @@ export interface UsageDetails {
         outputTokens: number;
         cacheReadTokens?: number;
         cacheWrite5mTokens?: number;
+        cacheWrite30mTokens?: number;
         cacheWrite1hTokens?: number;
+        cacheWrite12hTokens?: number;
     }>;
 }
 
+/**
+ * OpenAI `prompt_cache_options`, GPT-5.6 and later. `ttl` is the minimum
+ * lifetime of every cache entry the request writes; `12h` entries cost twice
+ * what `30m` entries do to write and only the Responses API writes them.
+ */
+export interface PromptCacheOptions {
+    mode?: 'implicit' | 'explicit';
+    ttl?: '30m' | '12h';
+}
+
 export interface ICompleteArguments {
     messages: PuterMessage[];
     provider?: string;
@@ -234,7 +252,9 @@ export interface ICompleteArguments {
     metadata?: Record<string, string>;
     prompt?: unknown;
     prompt_cache_key?: string;
-    prompt_cache_retention?: 'in-memory' | '24h' | undefined;
+    /** `in-memory` is accepted as a spelling of OpenAI's `in_memory`. */
+    prompt_cache_retention?: 'in-memory' | 'in_memory' | '24h' | undefined;
+    prompt_cache_options?: PromptCacheOptions;
     store?: boolean;
     top_p?: number;
     truncation?: 'auto' | 'disabled' | undefined;
diff --git a/src/backend/drivers/ai-chat/utils/OpenAIUtil.js b/src/backend/drivers/ai-chat/utils/OpenAIUtil.js
index fd42cb5d8..6c8ef5d1a 100644
--- a/src/backend/drivers/ai-chat/utils/OpenAIUtil.js
+++ b/src/backend/drivers/ai-chat/utils/OpenAIUtil.js
@@ -481,43 +481,86 @@ export const extractMeteredUsage = (usage) => {
 };
 
 /**
- * Chat Completions usage as it's metered: `prompt_tokens` reports cached reads
- * inside its count, so they come out of it and are priced only once, under
- * `cached_tokens`.
+ * @typedef {{
+ *     cached_tokens?: number | null;
+ *     cache_write_tokens?: number | null;
+ *     cache_write_tokens_details?: {
+ *         ttl_30m_tokens?: number | null;
+ *         ttl_12h_tokens?: number | null;
+ *     } | null;
+ * }} OpenAiCacheDetails
+ */
+
+/**
+ * OpenAI-shaped usage as it's metered. The prompt count reports cached reads
+ * and cache writes inside it, so they come out of it and are priced once each
+ * under their own keys: `cached_tokens` for reads, `cache_write_tokens` for
+ * writes at the model's default lifetime and `cache_write_12h_tokens` for
+ * writes at OpenAI's 12h lifetime. Without the per-lifetime breakdown every
+ * write is a default-lifetime write: Chat Completions writes no 12h entries,
+ * and Responses reports the breakdown whenever a request asked for them. Reads
+ * the Chat Completions (`prompt_tokens`) and Responses (`input_tokens`)
+ * spellings alike.
  *
- * @param {import('openai/resources/completions.mjs').CompletionUsage | undefined} usage
+ * @param {{
+ *           prompt_tokens?: number;
+ *           completion_tokens?: number;
+ *           prompt_tokens_details?: OpenAiCacheDetails | null;
+ *           input_tokens?: number;
+ *           output_tokens?: number;
+ *           input_tokens_details?: OpenAiCacheDetails | null;
+ *       }
+ *     | undefined} usage
  */
 export const splitCachedPrompt = (usage) => {
-    const details = usage?.prompt_tokens_details;
+    const details = usage?.prompt_tokens_details ?? usage?.input_tokens_details;
     const cachedTokens = details?.cached_tokens ?? 0;
-    // Moonshot counts the prompt tokens it wrote to its prefix cache here;
-    // they're billed at the model's write rate, not the plain prompt rate.
+    // Moonshot and GPT-5.6+ count the prompt tokens they wrote to the prefix
+    // cache here; they're billed at the model's write rate, not the prompt rate.
     const writeTokens =
         typeof details?.cache_write_tokens === 'number'
             ? details.cache_write_tokens
             : undefined;
+    const reported12h = details?.cache_write_tokens_details?.ttl_12h_tokens;
+    const write12hTokens =
+        typeof reported12h === 'number'
+            ? Math.min(reported12h, writeTokens ?? 0)
+            : undefined;
     return {
         prompt_tokens:
-            (usage?.prompt_tokens ?? 0) - cachedTokens - (writeTokens ?? 0),
-        completion_tokens: usage?.completion_tokens ?? 0,
+            (usage?.prompt_tokens ?? usage?.input_tokens ?? 0) -
+            cachedTokens -
+            (writeTokens ?? 0),
+        completion_tokens:
+            usage?.completion_tokens ?? usage?.output_tokens ?? 0,
         cached_tokens: cachedTokens,
         ...(writeTokens !== undefined
-            ? { cache_write_tokens: writeTokens }
+            ? { cache_write_tokens: writeTokens - (write12hTokens ?? 0) }
+            : {}),
+        ...(write12hTokens !== undefined
+            ? { cache_write_12h_tokens: write12hTokens }
             : {}),
     };
 };
 
 /**
- * The `{prompt_tokens, completion_tokens, cached_tokens, cache_write_tokens}`
- * shape every OpenAI-family `usage_calculator` already returns for billing,
- * mapped to the provider-neutral `UsageDetails` the end-of-stream/non-stream
- * result carries. `inputTokens`/`outputTokens` are the same numbers already
- * billed — this never introduces a new figure, only exposes the breakdown.
+ * The `{prompt_tokens, completion_tokens, cached_tokens, cache_write_tokens,
+ * cache_write_12h_tokens}` shape every OpenAI-family `usage_calculator` already
+ * returns for billing, mapped to the provider-neutral `UsageDetails` the
+ * end-of-stream/non-stream result carries. `inputTokens`/`outputTokens` are the
+ * same numbers already billed — this never introduces a new figure, only
+ * exposes the breakdown.
  *
  * @param {Record<string, number> | undefined | null} trackedUsage
+ * @param {{ writeTtl?: '5m' | '30m' }} [opts] The lifetime `cache_write_tokens`
+ *   were written with: 5m unless the provider says otherwise (OpenAI's default
+ *   entries live 30m).
  * @returns {import('../types.js').UsageDetails | undefined}
  */
-export const usageDetailsFromTrackedUsage = (trackedUsage) => {
+export const usageDetailsFromTrackedUsage = (
+    trackedUsage,
+    { writeTtl = '5m' } = {},
+) => {
     if (!trackedUsage || typeof trackedUsage !== 'object') return undefined;
     // OpenRouter, Infron and Ollama track `{prompt, completion,
     // input_cache_read}` instead; any other shape is left to the driver.
@@ -526,12 +569,19 @@ export const usageDetailsFromTrackedUsage = (trackedUsage) => {
     if (input === undefined && output === undefined) return undefined;
     const cacheRead =
         trackedUsage.cached_tokens ?? trackedUsage.input_cache_read;
+    const cacheWrite = trackedUsage.cache_write_tokens;
     return {
         inputTokens: input ?? 0,
         outputTokens: output ?? 0,
         ...(cacheRead ? { cacheReadTokens: cacheRead } : {}),
-        ...(trackedUsage.cache_write_tokens
-            ? { cacheWrite5mTokens: trackedUsage.cache_write_tokens }
+        ...(cacheWrite && writeTtl === '30m'
+            ? { cacheWrite30mTokens: cacheWrite }
+            : {}),
+        ...(cacheWrite && writeTtl !== '30m'
+            ? { cacheWrite5mTokens: cacheWrite }
+            : {}),
+        ...(trackedUsage.cache_write_12h_tokens
+            ? { cacheWrite12hTokens: trackedUsage.cache_write_12h_tokens }
             : {}),
     };
 };
@@ -864,12 +914,16 @@ export const create_chat_stream_handler_responses_api =
         // Missing usage is left undefined rather than fed to the calculator —
         // see the sibling handler above, including why usage is reported
         // before the block flushes.
+        let usageDetails;
         const usage = last_usage
             ? usage_calculator({
                   usage: last_usage,
                   webSearchCalls,
                   tool_usage: toolUsage,
                   setUsageCosts: (c) => chatStream.setUsageCosts(c),
+                  setUsageDetails: (d) => {
+                      usageDetails = d;
+                  },
               })
             : undefined;
         chatStream.reportUsage(usage);
@@ -877,7 +931,7 @@ export const create_chat_stream_handler_responses_api =
             reason:
                 incompleteReason ?? (sawFunctionCall ? 'tool_use' : 'end_turn'),
         });
-        const usageDetails = usageDetailsFromTrackedUsage(usage);
+        usageDetails ??= usageDetailsFromTrackedUsage(usage);
         if (usageDetails) chatStream.setUsageDetails(usageDetails);
 
         textblock.end();
@@ -1015,6 +1069,7 @@ export const handle_completion_output = async (
  *     webSearchCalls?: number;
  *     tool_usage?: Record<string, unknown>;
  *     setUsageCosts?: (costs: Record<string, number>) => void;
+ *     setUsageDetails?: (details: import('../types').UsageDetails) => void;
  * }) => unknown} params.usage_calculator
  * @param {() => Promise<void>} [params.finally_fn]
  * @returns {ReturnType<import('../types').IChatProvider['complete']>}
@@ -1156,12 +1211,15 @@ export const handle_completion_output_responses_api = async ({
               setUsageCosts: (c) => {
                   ret.usageCosts = c;
               },
+              setUsageDetails: (d) => {
+                  ret.usageDetails = d;
+              },
           })
         : {
               input_tokens: completion.usage.input_tokens,
               output_tokens: completion.usage.output_tokens,
           };
-    if (usage_calculator) {
+    if (usage_calculator && ret.usageDetails === undefined) {
         const usageDetails = usageDetailsFromTrackedUsage(ret.usage);
         if (usageDetails) ret.usageDetails = usageDetails;
     }
diff --git a/src/backend/drivers/ai-chat/utils/OpenAIUtil.test.ts b/src/backend/drivers/ai-chat/utils/OpenAIUtil.test.ts
index 4aa408000..f283f65a9 100644
--- a/src/backend/drivers/ai-chat/utils/OpenAIUtil.test.ts
+++ b/src/backend/drivers/ai-chat/utils/OpenAIUtil.test.ts
@@ -247,6 +247,40 @@ describe('usageDetailsFromTrackedUsage', () => {
         });
     });
 
+    it('labels cache writes by the lifetime the provider says it wrote them with', () => {
+        expect(
+            usageDetailsFromTrackedUsage(
+                {
+                    prompt_tokens: 10,
+                    completion_tokens: 5,
+                    cached_tokens: 3,
+                    cache_write_tokens: 11,
+                    cache_write_12h_tokens: 6012,
+                },
+                { writeTtl: '30m' },
+            ),
+        ).toEqual({
+            inputTokens: 10,
+            outputTokens: 5,
+            cacheReadTokens: 3,
+            cacheWrite30mTokens: 11,
+            cacheWrite12hTokens: 6012,
+        });
+        // Zero counts, as OpenAI reports on a cache hit, add no field.
+        expect(
+            usageDetailsFromTrackedUsage(
+                {
+                    prompt_tokens: 10,
+                    completion_tokens: 5,
+                    cached_tokens: 3,
+                    cache_write_tokens: 0,
+                    cache_write_12h_tokens: 0,
+                },
+                { writeTtl: '30m' },
+            ),
+        ).toEqual({ inputTokens: 10, outputTokens: 5, cacheReadTokens: 3 });
+    });
+
     it('returns undefined for a missing/non-object usage', () => {
         expect(usageDetailsFromTrackedUsage(undefined)).toBeUndefined();
         expect(usageDetailsFromTrackedUsage(null)).toBeUndefined();
@@ -962,6 +996,66 @@ describe('splitCachedPrompt', () => {
             cached_tokens: 3,
         });
     });
+
+    it('reads the Responses usage spelling', () => {
+        expect(
+            splitCachedPrompt({
+                input_tokens: 6026,
+                output_tokens: 5,
+                input_tokens_details: { cached_tokens: 0, cache_write_tokens: 6023 },
+            }),
+        ).toEqual({
+            prompt_tokens: 3,
+            completion_tokens: 5,
+            cached_tokens: 0,
+            cache_write_tokens: 6023,
+        });
+    });
+
+    it('splits 12h writes out of the write count when the breakdown is reported', () => {
+        // One request can write both lifetimes: an explicit 12h breakpoint
+        // plus the implicit 30m one OpenAI adds at the end of the prompt.
+        expect(
+            splitCachedPrompt({
+                input_tokens: 6026,
+                output_tokens: 5,
+                input_tokens_details: {
+                    cached_tokens: 0,
+                    cache_write_tokens: 6023,
+                    cache_write_tokens_details: {
+                        ttl_12h_tokens: 6012,
+                        ttl_30m_tokens: 11,
+                    },
+                },
+            }),
+        ).toEqual({
+            prompt_tokens: 3,
+            completion_tokens: 5,
+            cached_tokens: 0,
+            cache_write_tokens: 11,
+            cache_write_12h_tokens: 6012,
+        });
+    });
+
+    it('never reports more 12h writes than writes in total', () => {
+        expect(
+            splitCachedPrompt({
+                input_tokens: 100,
+                output_tokens: 1,
+                input_tokens_details: {
+                    cached_tokens: 0,
+                    cache_write_tokens: 40,
+                    cache_write_tokens_details: { ttl_12h_tokens: 50 },
+                },
+            }),
+        ).toEqual({
+            prompt_tokens: 60,
+            completion_tokens: 1,
+            cached_tokens: 0,
+            cache_write_tokens: 0,
+            cache_write_12h_tokens: 40,
+        });
+    });
 });
 
 // ── recorded usage costs ────────────────────────────────────────────
diff --git a/src/backend/drivers/ai-chat/utils/openaiParams.test.ts b/src/backend/drivers/ai-chat/utils/openaiParams.test.ts
index bd2801ca8..cc7ed5ff5 100644
--- a/src/backend/drivers/ai-chat/utils/openaiParams.test.ts
+++ b/src/backend/drivers/ai-chat/utils/openaiParams.test.ts
@@ -27,6 +27,8 @@ import {
     outputFormatFromResponsesText,
     outputFormatToResponseFormat,
     outputFormatToResponsesText,
+    promptCacheOptionsToWire,
+    promptCacheRetentionToWire,
     rejectStatefulResponsesFields,
     toolChoiceFromWire,
     toolChoiceToWire,
@@ -334,3 +336,50 @@ describe('rejectStatefulResponsesFields', () => {
         ).toThrow(/previous_response_id/);
     });
 });
+
+describe('promptCacheRetentionToWire', () => {
+    it('spells the in-memory retention the way the upstreams expect', () => {
+        expect(promptCacheRetentionToWire('in-memory')).toBe('in_memory');
+        expect(promptCacheRetentionToWire('in_memory')).toBe('in_memory');
+        expect(promptCacheRetentionToWire('24h')).toBe('24h');
+        expect(promptCacheRetentionToWire(undefined)).toBeUndefined();
+    });
+});
+
+describe('promptCacheOptionsToWire', () => {
+    it('forwards mode and ttl and nothing else', () => {
+        expect(
+            promptCacheOptionsToWire({
+                mode: 'explicit',
+                ttl: '12h',
+                prewarm: true,
+                comparison_response_id: 'resp_1',
+            }),
+        ).toEqual({ mode: 'explicit', ttl: '12h' });
+        expect(promptCacheOptionsToWire({ ttl: '30m' })).toEqual({
+            ttl: '30m',
+        });
+    });
+
+    it('sends nothing for an absent or empty object', () => {
+        expect(promptCacheOptionsToWire(undefined)).toBeUndefined();
+        expect(promptCacheOptionsToWire(null)).toBeUndefined();
+        expect(promptCacheOptionsToWire({})).toBeUndefined();
+        expect(promptCacheOptionsToWire({ prewarm: true })).toBeUndefined();
+    });
+
+    it('rejects a lifetime or mode OpenAI does not offer', () => {
+        expect(() => promptCacheOptionsToWire({ ttl: '2h' })).toThrow(
+            expect.objectContaining({ statusCode: 400 }),
+        );
+        expect(() => promptCacheOptionsToWire({ ttl: '24h' })).toThrow(
+            /30m.*12h/,
+        );
+        expect(() => promptCacheOptionsToWire({ mode: 'auto' })).toThrow(
+            /implicit.*explicit/,
+        );
+        expect(() => promptCacheOptionsToWire('12h')).toThrow(
+            /must be an object/,
+        );
+    });
+});
diff --git a/src/backend/drivers/ai-chat/utils/openaiParams.ts b/src/backend/drivers/ai-chat/utils/openaiParams.ts
index eca62e486..8bb87d1d0 100644
--- a/src/backend/drivers/ai-chat/utils/openaiParams.ts
+++ b/src/backend/drivers/ai-chat/utils/openaiParams.ts
@@ -29,6 +29,7 @@ import { HttpError } from '../../../core/http/HttpError.js';
 import type {
     ICompleteArguments,
     OutputFormat,
+    PromptCacheOptions,
     ReasoningEffort,
     ToolChoice,
 } from '../types.js';
@@ -305,6 +306,60 @@ export const openAICompatParams = (
     return out;
 };
 
+// -- prompt caching ----------------------------------------------------------
+
+/**
+ * The wire spelling of `prompt_cache_retention`. Puter also accepts the
+ * hyphenated `in-memory`, which every OpenAI-shaped upstream rejects.
+ */
+export const promptCacheRetentionToWire = (
+    retention: ICompleteArguments['prompt_cache_retention'],
+): 'in_memory' | '24h' | undefined =>
+    retention === 'in-memory' ? 'in_memory' : retention;
+
+const PROMPT_CACHE_MODES = new Set(['implicit', 'explicit']);
+const PROMPT_CACHE_TTLS = new Set(['30m', '12h']);
+
+/**
+ * `prompt_cache_options` as forwarded upstream: `mode` and `ttl` only, each
+ * checked against the values OpenAI accepts, so a bad value fails here with a
+ * clear message instead of as an upstream 400 the fallback loop may hide.
+ * `comparison_response_id` names a stored response, which Puter never keeps,
+ * and `prewarm` is dropped with it.
+ */
+export const promptCacheOptionsToWire = (
+    options: unknown,
+): PromptCacheOptions | undefined => {
+    if (options === undefined || options === null) return undefined;
+    if (typeof options !== 'object' || Array.isArray(options)) {
+        throw new HttpError(400, '`prompt_cache_options` must be an object', {
+            legacyCode: 'bad_request',
+        });
+    }
+    const { mode, ttl } = options as Record<string, unknown>;
+    if (mode !== undefined && !PROMPT_CACHE_MODES.has(mode as string)) {
+        throw new HttpError(
+            400,
+            '`prompt_cache_options.mode` must be `implicit` or `explicit`',
+            { legacyCode: 'bad_request' },
+        );
+    }
+    if (ttl !== undefined && !PROMPT_CACHE_TTLS.has(ttl as string)) {
+        throw new HttpError(
+            400,
+            '`prompt_cache_options.ttl` must be `30m` or `12h`',
+            { legacyCode: 'bad_request' },
+        );
+    }
+    const wire: PromptCacheOptions = {
+        ...(mode !== undefined
+            ? { mode: mode as PromptCacheOptions['mode'] }
+            : {}),
+        ...(ttl !== undefined ? { ttl: ttl as PromptCacheOptions['ttl'] } : {}),
+    };
+    return Object.keys(wire).length ? wire : undefined;
+};
+
 // -- Responses server-side state ---------------------------------------------
 
 const STATEFUL_RESPONSES_FIELDS = [
diff --git a/src/docs/src/AI/chat.md b/src/docs/src/AI/chat.md
index 48ebf291f..1192baaf6 100755
--- a/src/docs/src/AI/chat.md
+++ b/src/docs/src/AI/chat.md
@@ -314,6 +314,21 @@ You can find the implementation in our [prompt caching example](/playground/ai-c
 
 Moonshot's Kimi K3 and Kimi K3.1 Pro models cache prompt prefixes on their own and take no `cache_control`. Their `usage` reports the tokens read from the cache as `cached_tokens` and the tokens written to it as `cache_write_tokens`. Each is billed at the model's own rate from the [AI models list](https://developer.puter.com/ai/models/).
 
+OpenAI models cache prompt prefixes on their own too. Requests from the same app and user share one cache by default, and you can pick the cache with `prompt_cache_key`. Their `usage` reports the tokens read from the cache as `cached_tokens`.
+
+GPT-5.6 and later models charge for cache writes and let you choose how long an entry lives. Pass `prompt_cache_options` with a `ttl` of `"30m"` (the default) or `"12h"`. The `usage` reports the tokens written with the 30 minute lifetime as `cache_write_tokens` and the tokens written with the 12 hour lifetime as `cache_write_12h_tokens`. Writing a 30 minute entry costs 1.25 times the model's input rate, and writing a 12 hour entry costs 2.5 times the input rate. Reads cost the same for both lifetimes. The 12 hour lifetime is only available through the OpenAI Responses API, so a request with `ttl: "12h"` is sent there.
+
+```js
+puter.ai.chat('<your message>', {
+    model: 'gpt-6-luna',
+    prompt_cache_options: { ttl: '12h' }
+});
+```
+
+Older OpenAI models charge nothing for cache writes. Pass `prompt_cache_retention` with `"in_memory"` for an entry that lives a few minutes or `"24h"` for one that can live up to a day. The 24 hour option is the default, and GPT-5.5 and later models only support it.
+
+The `usageDetails` object on every result carries the same counts under provider-neutral names, with one field per lifetime, such as `cacheWrite30mTokens` and `cacheWrite12hTokens`. See the [ChatResponse](/Objects/chatresponse/) object for the full list.
+
 ## Compaction
 
 For long, multi-turn conversations that you keep on the client, enable
diff --git a/src/docs/src/Objects/chatresponse.md b/src/docs/src/Objects/chatresponse.md
index 628f6a678..2fc6a81ca 100644
--- a/src/docs/src/Objects/chatresponse.md
+++ b/src/docs/src/Objects/chatresponse.md
@@ -64,7 +64,7 @@ Extra detail on why generation stopped (e.g. a refusal classification). Provider
 
 #### `usageDetails` (Object)
 
-A provider-neutral usage breakdown, present alongside `usage` on every result. `inputTokens` excludes cache reads/writes; `outputTokens` includes reasoning tokens. Fields: `inputTokens`, `outputTokens`, `cacheReadTokens`, `cacheWrite5mTokens`, `cacheWrite1hTokens`, `reasoningTokens`, `webSearchRequests`, `webFetchRequests`, `speed` (`"fast"` or `"standard"`), `serviceTier`, and `iterations` (a per-pass breakdown when the upstream ran several passes, e.g. compaction or an advisor sub-call).
+A provider-neutral usage breakdown, present alongside `usage` on every result. `inputTokens` excludes cache reads/writes; `outputTokens` includes reasoning tokens. Fields: `inputTokens`, `outputTokens`, `cacheReadTokens`, `cacheWrite5mTokens`, `cacheWrite30mTokens`, `cacheWrite1hTokens`, `cacheWrite12hTokens`, `reasoningTokens`, `webSearchRequests`, `webFetchRequests`, `speed` (`"fast"` or `"standard"`), `serviceTier`, and `iterations` (a per-pass breakdown when the upstream ran several passes, e.g. compaction or an advisor sub-call). Each `cacheWrite*Tokens` field counts the tokens written to the cache with that lifetime: Claude and Moonshot write 5 minute and 1 hour entries, OpenAI writes 30 minute and 12 hour entries.
 
 Prefer `usageDetails` over `usage` for anything beyond the raw billing totals. Claude's `usage.thinking_tokens` is informational: it's included in `output_tokens` and not billed separately — `usageDetails.reasoningTokens` carries the same count.
 
diff --git a/src/docs/src/Objects/chatresponsechunk.md b/src/docs/src/Objects/chatresponsechunk.md
index b5a147f78..28104d9ed 100644
--- a/src/docs/src/Objects/chatresponsechunk.md
+++ b/src/docs/src/Objects/chatresponsechunk.md
@@ -102,7 +102,7 @@ Extra detail on why generation stopped (e.g. a refusal classification). Provider
 
 #### `usageDetails` (Object)
 
-A provider-neutral usage breakdown, present on the final `usage` chunk. `inputTokens` excludes cache reads/writes; `outputTokens` includes reasoning tokens. Fields: `inputTokens`, `outputTokens`, `cacheReadTokens`, `cacheWrite5mTokens`, `cacheWrite1hTokens`, `reasoningTokens`, `webSearchRequests`, `webFetchRequests`, `speed` (`"fast"` or `"standard"`), `serviceTier`, and `iterations` (a per-pass breakdown when the upstream ran several passes, e.g. compaction or an advisor sub-call).
+A provider-neutral usage breakdown, present on the final `usage` chunk. `inputTokens` excludes cache reads/writes; `outputTokens` includes reasoning tokens. Fields: `inputTokens`, `outputTokens`, `cacheReadTokens`, `cacheWrite5mTokens`, `cacheWrite30mTokens`, `cacheWrite1hTokens`, `cacheWrite12hTokens`, `reasoningTokens`, `webSearchRequests`, `webFetchRequests`, `speed` (`"fast"` or `"standard"`), `serviceTier`, and `iterations` (a per-pass breakdown when the upstream ran several passes, e.g. compaction or an advisor sub-call). Each `cacheWrite*Tokens` field counts the tokens written to the cache with that lifetime: Claude and Moonshot write 5 minute and 1 hour entries, OpenAI writes 30 minute and 12 hour entries.
 
 #### `message` (String)
 
diff --git a/src/puter-js/src/modules/ai/ai.test.js b/src/puter-js/src/modules/ai/ai.test.js
index ff31c1938..f5f14dc9e 100644
--- a/src/puter-js/src/modules/ai/ai.test.js
+++ b/src/puter-js/src/modules/ai/ai.test.js
@@ -171,6 +171,20 @@ describe('ai.chat driver payloads', () => {
         });
     });
 
+    it('chat(prompt, options) forwards the OpenAI prompt-cache options', async () => {
+        await ai.chat('hello', {
+            prompt_cache_key: 'ck',
+            prompt_cache_retention: '24h',
+            prompt_cache_options: { mode: 'explicit', ttl: '12h' },
+        });
+        expect(lastBody().args).toEqual({
+            messages: [{ content: 'hello' }],
+            prompt_cache_key: 'ck',
+            prompt_cache_retention: '24h',
+            prompt_cache_options: { mode: 'explicit', ttl: '12h' },
+        });
+    });
+
     it('chat(prompt, options) forwards temperature: 0 and max_tokens: 0', async () => {
         await ai.chat('hello', {
             temperature: 0,
diff --git a/src/puter-js/src/modules/ai/chat.js b/src/puter-js/src/modules/ai/chat.js
index 0f4384a48..9d1093fa1 100644
--- a/src/puter-js/src/modules/ai/chat.js
+++ b/src/puter-js/src/modules/ai/chat.js
@@ -27,6 +27,9 @@ const PARAMS_TO_PASS = [
     'outputFormat',
     'thinking',
     'streamToolInput',
+    'prompt_cache_key',
+    'prompt_cache_retention',
+    'prompt_cache_options',
 ];
 
 // Parameters renamed between the SDK's camelCase option and the driver's
diff --git a/src/puter-js/src/modules/ai/types.js b/src/puter-js/src/modules/ai/types.js
index 0e6aa7218..2b9552cf4 100644
--- a/src/puter-js/src/modules/ai/types.js
+++ b/src/puter-js/src/modules/ai/types.js
@@ -115,6 +115,14 @@
  * @property {boolean} [streamToolInput] Streaming only: emit incremental `tool_use_start` /
  * `tool_input_delta` chunks as a tool call's arguments are generated, instead of a single `tool_use`
  * chunk once the call completes.
+ * @property {string} [prompt_cache_key] OpenAI models: which prompt cache the request reads from and
+ * writes to. Defaults to one cache per app and user.
+ * @property {'in_memory' | '24h'} [prompt_cache_retention] OpenAI models before GPT-5.6: how long a
+ * cache entry may live. `'24h'` is the default and the only value GPT-5.5 and later accept.
+ * @property {{ mode?: 'implicit' | 'explicit', ttl?: '30m' | '12h' }} [prompt_cache_options] OpenAI
+ * GPT-5.6 and later: `ttl` is the minimum lifetime of every cache entry the request writes. A `'12h'`
+ * entry costs twice as much to write as the default `'30m'` one and is served through the Responses
+ * API. `mode: 'explicit'` only writes at the `prompt_cache_breakpoint` markers in your messages.
  */
 
 /**
@@ -132,14 +140,16 @@
  * @property {number} inputTokens
  * @property {number} outputTokens
  * @property {number} [cacheReadTokens]
- * @property {number} [cacheWrite5mTokens]
- * @property {number} [cacheWrite1hTokens]
+ * @property {number} [cacheWrite5mTokens] Tokens written to the cache with a 5 minute lifetime (Claude, Moonshot).
+ * @property {number} [cacheWrite30mTokens] Tokens written with a 30 minute lifetime (OpenAI's default).
+ * @property {number} [cacheWrite1hTokens] Tokens written with a 1 hour lifetime (Claude, Moonshot).
+ * @property {number} [cacheWrite12hTokens] Tokens written with a 12 hour lifetime (OpenAI, `prompt_cache_options.ttl: '12h'`).
  * @property {number} [reasoningTokens]
  * @property {number} [webSearchRequests]
  * @property {number} [webFetchRequests]
  * @property {'fast' | 'standard'} [speed]
  * @property {string} [serviceTier]
- * @property {Array<{ type: string, model?: string, inputTokens: number, outputTokens: number, cacheReadTokens?: number, cacheWrite5mTokens?: number, cacheWrite1hTokens?: number }>} [iterations]
+ * @property {Array<{ type: string, model?: string, inputTokens: number, outputTokens: number, cacheReadTokens?: number, cacheWrite5mTokens?: number, cacheWrite30mTokens?: number, cacheWrite1hTokens?: number, cacheWrite12hTokens?: number }>} [iterations]
  * Per-pass breakdown when the upstream ran several passes (compaction, an advisor sub-call).
  */