{"uid":"cap_U3Sz0xb6yk2opVkNxbOHc","slug":"model-access-gateway-gpt-oss-120b-chat-completions-x402-usdc-745297f6","name":"Model Access Gateway – GPT-OSS-120B Chat Completions (x402, USDC)","description":"LLM inference API: OpenAI-compatible chat completions for 136 AI models (Claude, GPT, Gemini, Grok, DeepSeek, Qwen, Kimi, GLM), paid per call in USDC on Base with x402. No account, no API key, automatic refund if the model fails.","url":"https://modelaccessgateway.com/llm/gpt-oss-120b?utm_source=zero.xyz","method":"POST","headers":{},"bodySchema":{"type":"object","properties":{"model":{"type":"string","description":"Optional: fixed by the route (openai/gpt-oss-120b)"},"tools":{"type":"array"},"stream":{"type":"boolean","description":"true: server-sent events after payment"},"messages":{"type":"array","items":{"type":"object","required":["role"],"properties":{"role":{"enum":["system","user","assistant","tool","developer"],"type":"string"},"content":{"type":["string","array","null"]}}},"minItems":1},"max_tokens":{"type":"integer","maximum":16384,"minimum":1,"description":"Optional, default 4096"},"temperature":{"type":"number","maximum":2,"minimum":0},"response_format":{"type":"object"}}},"responseSchema":{"type":"json","example":{"id":"chatcmpl-7f3c2a91","model":"openai/gpt-oss-120b","usage":{"total_tokens":10,"prompt_tokens":9,"completion_tokens":1},"object":"chat.completion","choices":[{"index":0,"message":{"role":"assistant","content":"OK"},"finish_reason":"stop"}],"created":1791979200}},"example":null,"exampleRequest":null,"tags":["x402"],"displayCostAmount":"0.001","displayCostAsset":"USDC","priceDynamic":false,"priceHint":null,"priceStatus":"priced","priceSource":"probe","requiresHandshake":false,"reviewCount":0,"rating":{"score":"0.00","successRate":"0.00","reviews":0,"stars":null,"state":"unrated"},"availabilityStatus":"unknown","priceObserved":null,"sessionDeposit":null,"pricing":{"kind":"static","summary":"$0.001/call","primary":{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.001","per":"call","confidence":"exact"},"accepted":[{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.001","per":"call","confidence":"exact"}]},"paymentMethods":[{"uid":"pm_1NORmSmsRdniUQ6_IagH0","protocol":"x402","methodType":"crypto","chain":"base","mode":"charge","costAmount":"0.001","costPer":"request","priority":0,"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","unit":"request","depositMicros":null,"planRef":null}],"brandName":null,"brandSlug":null,"brandBaseUrl":null,"brandDocsUrl":null,"whatItDoes":"Runs OpenAI-compatible chat completions against the GPT-OSS-120B model, billed per call in USDC on Base via x402 with no account or API key required.","exampleAgentPrompt":"Using Model Access Gateway's pay-per-call setup, send a chat message to GPT-OSS-120B asking it to summarize the following text in 3 bullet points — pay in USDC, stream the response, and set max_tokens to 512.","exampleUseCases":[{"title":"Anonymous one-off LLM query","prompt":"I need to ask a 120B-parameter open-source GPT model a single question without creating any accounts — just pay a fraction of a cent in USDC and get the answer back. Ask it: 'What are three key differences between TCP and UDP?'"},{"title":"Streaming AI assistant in an app","prompt":"In my app I want to stream a GPT-OSS-120B response to the user as it generates — send the system message 'You are a helpful coding assistant', the user message 'Explain async/await in Python with an example', enable streaming, and cap the output at 1024 tokens."},{"title":"Structured JSON output from LLM","prompt":"Call the GPT-OSS-120B model with the prompt 'Extract the company name, date, and total amount from this invoice text: Acme Corp, Jan 15 2025, $4,320' and return the result as structured JSON — use response_format to enforce JSON output."}],"resultDescription":"Returns an OpenAI-compatible chat.completion JSON object containing the assistant's generated message, the finish reason (stop, length, tool_calls, etc.), token usage breakdown (prompt, completion, total), a completion ID, and the model name. When streaming is enabled, delivers server-sent events incrementally until the response is complete.","failureModes":["Payment rejected or insufficient USDC balance — x402 payment handshake fails, no completion returned and automatic refund issued","Model backend unavailable — upstream model error triggers automatic refund per gateway policy","Invalid messages array (empty or missing required role field) — 400 validation error","max_tokens exceeds 16384 limit — schema validation failure","Temperature out of 0–2 range — request rejected with validation error","Network timeout on long completions — partial response or no response, refund policy applies"],"whenToPreferThis":"Choose this endpoint when you need OpenAI-compatible GPT-OSS-120B inference without an API subscription, account registration, or stored credentials — ideal for agentic workflows that pay per call in USDC via x402 on Base. Prefer it over subscription-gated APIs when cost isolation per call matters, when operating anonymously, or when building agents that need built-in crypto micropayment flows. The automatic refund guarantee on model failure makes it lower-risk than raw provider APIs for unreliable or experimental workloads.","instructions":null,"reviewSummary":null,"reviewSummaryHighlights":null,"reviewSummaryConcerns":null,"reviewSummaryGeneratedAt":null,"activationCount":0,"lastUsedAt":null,"lastSuccessfullyRanAt":null,"lastHealthCheckAt":"2026-10-18T06:35:21.719Z","isFirstParty":false,"canonicalSlug":"model-access-gateway-gpt-oss-120b-chat-completions-x402-usdc-745297f6"}